Description: This document describes the GNU CLISP - an implementation of the ANSI CL standard. See for instructions on how to report bugs (both in the software and the documentaion). See for information on CLISP support.
Keywords: Lisp, Common Lisp, CLISP
Date: 'generated: 2020-06-22 00:46:14+02:00'

# Implementation Notes for GNU CLISP

## These notes document CLISP version 2.49.93+

###

### Bruno Haible

The original author and long-time maintainer.

### Michael Stoll

The original author.

### Sam Steingold

Co-maintainer since 1998.

### Others

See `COPYRIGHT` for the list of other contributors and the license.

Copyright © 1992-2010 Bruno Haible

Copyright © 1998-2010 Sam Steingold

Legal Status of the CLISP Implementation Notes

These notes are dually licensed under GNU FDL and GNU GPL. This means that you can redistribute this document under either of these two licenses, at your choice.

These notes are covered by the GNU FDL. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License (FDL), either version 1.2 of the License, or (at your option) any later version published by the Free Software Foundation (FSF); with no Invariant Sections, with no Front-Cover Text, and with no Back-Cover Texts. A copy of the license is included in Appendix B, GNU Free Documentation License.

These notes are covered by the GNU GPL. This document documents free software; you can redistribute it and/or modify it under the terms of the GNU General Public License (GPL), either version 2 of the License, or (at your option) any later version published by the Free Software Foundation (FSF). A copy of the license is included in Appendix C, GNU General Public License.

CLISP Release History
Release 1 | April 1987 - July 1992 | bruno
The project was started when both original authors, Bruno Haible and Michael Stoll, were students in Germany. The original version was for Atari ST only, written in 68000 assembly language and Common Lisp.
Release 2.0 | 1992-10-09 | bruno
the USENET newsgroup comp.os.linux announcement (Linux binaries only)
Release 2.1 | 1993-01-01 | bruno
The first portable release, with source, released under GNU GPL. Supported platforms: Atari ST, Amiga 500-2000, DOS (emx, djgpp), OS/2 (emx), Unix (Linux, Sun4, Sun386, HP9000/800).
Release 2.1.1 | 1993-01-11 | bruno
Release 2.1.2 | 1993-02-01 | bruno
Release 2.1.3 | 1993-02-03 | bruno
Release 2.2 | 1993-02-21 | bruno
Add test suite.
Release 2.2.1 | 1993-03-04 | bruno
Release 2.2.2 | 1993-03-19 | bruno
`CUSTOM:*EDITOR*`
Release 2.3 | 1993-03-30 | bruno
`LOAD-TIME-VALUE` `EXT:DEFAULT-DIRECTORY`
Release 2.3.1 | 1993-04-05 | bruno
Release 2.4 | 1993-05-24 | bruno
`DEFPACKAGE` `FUNCTION-LAMBDA-EXPRESSION` Section 32.1, “Random Screen Access”
Release 2.5 | 1993-06-29 | bruno
`SETF` function names. `PRINT-UNREADABLE-OBJECT` `SYMBOL-MACROLET`
Release 2.5.1 | 1993-07-17 | bruno
immutable objects
Release 2.6 | 1993-08-22 | bruno
Changed bytecode format “CLOS” package: `DEFCLASS`, `DEFMETHOD`, `DEFGENERIC`, `GENERIC-FUNCTION`, `CLOS:GENERIC-FLET`, `CLOS:GENERIC-LABELS`, `WITH-SLOTS`, `WITH-ACCESSORS`, `FIND-CLASS`, (`SETF` `FIND-CLASS`), `CLASS-OF`, `CLASS-NAME`, (`SETF` `CLASS-NAME`), `SLOT-VALUE`, `SLOT-BOUNDP`, `SLOT-MAKUNBOUND`, `SLOT-EXISTS-P`, `CALL-NEXT-METHOD`, `NEXT-METHOD-P`, `NO-APPLICABLE-METHOD`, `CLOS:NO-PRIMARY-METHOD`, `NO-NEXT-METHOD`, `FIND-METHOD`, `ADD-METHOD`, `REMOVE-METHOD`, `COMPUTE-APPLICABLE-METHODS`, `METHOD-QUALIFIERS`, `FUNCTION-KEYWORDS`, `SLOT-MISSING`, `SLOT-UNBOUND`, `PRINT-OBJECT`, `DESCRIBE-OBJECT`, `MAKE-INSTANCE`, `INITIALIZE-INSTANCE`, `REINITIALIZE-INSTANCE`, `SHARED-INITIALIZE`
Release 2.6.1 | 1993-09-01 | bruno
Changed bytecode format
Release 2.7 | 1993-09-27 | bruno
top-level forms `DECLAIM`
Release 2.8 | 1993-11-08 | bruno
“COMMON-LISP”, “COMMON-LISP-USER” New module: STDWIN
Release 2.9 | 1994-01-08 | bruno
Changed bytecode format `DEFINE-CONDITION`, `IGNORE-ERRORS`, `HANDLER-CASE`, `HANDLER-BIND`, `RESTART-CASE`, `EXT:WITH-RESTARTS`, `WITH-SIMPLE-RESTART`, `RESTART-BIND`, `WITH-CONDITION-RESTARTS`, `RESTART`, `CONDITION`, `SERIOUS-CONDITION`, `ERROR`, `PROGRAM-ERROR`, `CONTROL-ERROR`, `ARITHMETIC-ERROR`, `DIVISION-BY-ZERO`, `FLOATING-POINT-OVERFLOW`, `FLOATING-POINT-UNDERFLOW`, `CELL-ERROR`, `UNBOUND-VARIABLE`, `UNDEFINED-FUNCTION`, `TYPE-ERROR`, `PACKAGE-ERROR`, `STREAM-ERROR`, `END-OF-FILE`, `FILE-ERROR`, `STORAGE-CONDITION`, `WARNING`, `SIMPLE-CONDITION`, `SIMPLE-ERROR`, `SIMPLE-TYPE-ERROR`, `SIMPLE-WARNING`, `MAKE-CONDITION`, `SIGNAL`, `COMPUTE-RESTARTS`, `FIND-RESTART`, `INVOKE-RESTART`, `INVOKE-RESTART-INTERACTIVELY`, `ABORT`, `CONTINUE`, `MUFFLE-WARNING`, `STORE-VALUE`, `USE-VALUE`, `INVOKE-DEBUGGER`, `RESTART-NAME`, `ARITHMETIC-ERROR-OPERATION`, `ARITHMETIC-ERROR-OPERANDS`, `CELL-ERROR-NAME`, `TYPE-ERROR-DATUM`, `TYPE-ERROR-EXPECTED-TYPE`, `PACKAGE-ERROR-PACKAGE`, `STREAM-ERROR-STREAM`, `FILE-ERROR-PATHNAME`, `EXT:SIMPLE-CONDITION-FORMAT-STRING`, `SIMPLE-CONDITION-FORMAT-ARGUMENTS`, `*BREAK-ON-SIGNALS*`, `*DEBUGGER-HOOK*`, `*PRINT-READABLY*`
Release 2.10 | 1994-06-22 | bruno
`EXT:READ-CHAR-SEQUENCE`, `EXT:WRITE-CHAR-SEQUENCE`, `EXT:READ-BYTE-SEQUENCE`, `EXT:WRITE-BYTE-SEQUENCE` Section 31.6, “Generic streams”
Release 2.11 | 1994-07-04 | bruno
`LOOP`, `LOOP-FINISH`, `MAP-INTO` `LEAST-POSITIVE-NORMALIZED-SHORT-FLOAT`, `LEAST-NEGATIVE-NORMALIZED-SHORT-FLOAT`, `LEAST-POSITIVE-NORMALIZED-SINGLE-FLOAT`, `LEAST-NEGATIVE-NORMALIZED-SINGLE-FLOAT`, `LEAST-POSITIVE-NORMALIZED-DOUBLE-FLOAT`, `LEAST-NEGATIVE-NORMALIZED-DOUBLE-FLOAT`, `LEAST-POSITIVE-NORMALIZED-LONG-FLOAT`, `LEAST-NEGATIVE-NORMALIZED-LONG-FLOAT`
Release 2.12 | 1994-08-23 | bruno
generational garbage-collection `DESTRUCTURING-BIND` `EXT:UNCOMPILE`
Release 2.12.1 | 1994-09-01 | bruno
Release 2.13 | 1994-10-26 | bruno
Changed bytecode format `WILD-PATHNAME-P`, `PATHNAME-MATCH-P`, `TRANSLATE-PATHNAME`, `LOGICAL-PATHNAME`, `LOGICAL-PATHNAME-TRANSLATIONS`, `TRANSLATE-LOGICAL-PATHNAME`, `LOAD-LOGICAL-PATHNAME-TRANSLATIONS`, `COMPILE-FILE-PATHNAME`
Release 2.13.1 | 1995-01-01 | bruno
Changed bytecode format
Release 2.14 | 1995-04-04 | bruno
“FFI” `ROW-MAJOR-AREF`, `DELETE-PACKAGE`, `EXT:MUFFLE-CERRORS`, `EXT:APPEASE-CERRORS`, `EXT:EXIT-ON-ERROR`
Release 2.15 | 1995-04-25 | bruno
New modules: `wildcard`, `regexp` `FORMATTER`, `EXT:FINALIZE` `FILE-STREAM`, `SYNONYM-STREAM`, `BROADCAST-STREAM`, `CONCATENATED-STREAM`, `TWO-WAY-STREAM`, `ECHO-STREAM`, `STRING-STREAM`, `OPEN-STREAM-P`, `SYNONYM-STREAM-SYMBOL`, `BROADCAST-STREAM-STREAMS`, `CONCATENATED-STREAM-STREAMS`, `TWO-WAY-STREAM-INPUT-STREAM`, `TWO-WAY-STREAM-OUTPUT-STREAM`, `ECHO-STREAM-INPUT-STREAM`, `ECHO-STREAM-OUTPUT-STREAM`, `PRINT-NOT-READABLE`, `PRINT-NOT-READABLE-OBJECT`
Release 2.16 | 1995-06-23 | bruno
Changed bytecode format `COMPLEMENT`, `WITH-STANDARD-IO-SYNTAX`, `DYNAMIC-EXTENT`, `LAMBDA`, `IGNORABLE`, `CONSTANTLY` `WITH-HASH-TABLE-ITERATOR`, `HASH-TABLE-REHASH-SIZE`, `HASH-TABLE-REHASH-THRESHOLD`, `HASH-TABLE-SIZE`, `HASH-TABLE-TEST`
Release 2.17 | 1996-07-21 | bruno
Changed bytecode format `SOCKET:SOCKET-SERVER`, `SOCKET:SOCKET-SERVER-CLOSE`, `SOCKET:SOCKET-SERVER-PORT`, `SOCKET:SOCKET-WAIT`, `SOCKET:SOCKET-ACCEPT`, `SOCKET:SOCKET-CONNECT`, `SOCKET:SOCKET-STREAM-HOST`, `SOCKET:SOCKET-STREAM-PORT`, `SOCKET:SOCKET-SERVICE-PORT`, `SOCKET:SOCKET-STREAM-PEER`
Release 2.18 | 1997-05-03 | bruno
`I18N:DEFLANGUAGE`, `I18N:DEFINTERNATIONAL`, `I18N:DEFLOCALIZED` `CUSTOM:*LOAD-COMPILING*`
Release 2.19 | 1997-08-07 | bruno
CLX
Release 2.20 | 1997-09-25 | bruno
`*READ-EVAL*` `EXT:TIMES`
Release 2.20.1 | 1997-12-06 | bruno
Release 2.21 | 1998-09-09 | bruno
Changed bytecode format Removed module STDWIN. `CUSTOM:*WARN-ON-FLOATING-POINT-CONTAGION*`, `CUSTOM:*FLOATING-POINT-CONTAGION-ANSI*`, `FLOATING-POINT-INEXACT`, `FLOATING-POINT-INVALID-OPERATION` `EXT:PROBE-DIRECTORY`, `ENSURE-DIRECTORIES-EXIST` `*PRINT-RIGHT-MARGIN*`, `ARRAY-DISPLACEMENT` `BOOLEAN`, `COPY-STRUCTURE`, `GENERIC-FUNCTION`, `STRUCTURE-OBJECT`, `CLASS`, `METHOD`, `SPECIAL-OPERATOR-P`
Release 2.22 | 1999-01-08 | bruno
Changed bytecode format `BASE-CHAR`, `EXTENDED-CHAR`, `BASE-STRING`, `SIMPLE-BASE-STRING` `GET-SETF-EXPANSION`, `DEFINE-SETF-EXPANDER` `PARSE-ERROR`, `READER-ERROR` `UNBOUND-SLOT-INSTANCE` `SOCKET:SOCKET-STREAM-LOCAL`, `SOCKET:SOCKET-SERVER-HOST`
Release 2.23 | 1999-07-22 | bruno
New module: `postgresql` UNICODE, “CHARSET”, `CUSTOM:*DEFAULT-FILE-ENCODING*`, `CUSTOM:*PATHNAME-ENCODING*`, `CUSTOM:*TERMINAL-ENCODING*`, `CUSTOM:*MISC-ENCODING*` `CUSTOM:*FOREIGN-ENCODING*`, `AFFI:*FOREIGN-ENCODING*` Chapter 30, Gray streams `STREAM-EXTERNAL-FORMAT` `WITH-PACKAGE-ITERATOR` `ALLOCATE-INSTANCE` Section 31.7.1, “Weak Pointers” `EXT:READ-INTEGER`, `EXT:WRITE-INTEGER` `SIMPLE-CONDITION-FORMAT-CONTROL`
Release 2.24 | 2000-03-06 | bruno
`EXT:READ-FLOAT`, `EXT:WRITE-FLOAT` `EXT:CHAR-WIDTH`, `EXT:STRING-WIDTH` `WITH-COMPILATION-UNIT`
Release 2.25 | 2001-03-15 | sds
Changed bytecode format `INSPECT`, `EXT:CLHS` `EXT:CONVERT-STRING-FROM-BYTES`, `EXT:CONVERT-STRING-TO-BYTES` `EXT:READ-BYTE-LOOKAHEAD`, `GRAY:STREAM-READ-BYTE-LOOKAHEAD`, `EXT:READ-BYTE-WILL-HANG-P`, `GRAY:STREAM-READ-BYTE-WILL-HANG-P`, `EXT:READ-BYTE-NO-HANG`, `GRAY:STREAM-READ-BYTE-NO-HANG` Win32 improvements (UNC pathnames, registry, screen)
Release 2.25.1 | 2001-04-06 | sds
Release 2.26 | 2001-05-23 | sds
Changed bytecode format dropped CLtL1, added `:LISP=CL` to `*FEATURES*` `DEFINE-COMPILER-MACRO` `UPGRADED-COMPLEX-PART-TYPE` `EXT:RUN-SHELL-COMMAND`, `EXT:RUN-PROGRAM` accept `:WAIT` compiler checks function call signatures
Release 2.27 | 2001-07-17 | sds
`(`SETF` `EXT:GETENV`)` `src/install.bat`
Release 2.28 | 2002-03-03 | sds
Changed bytecode format [ANSI CL standard] Pretty-Printer `MAKE-LOAD-FORM`, `MAKE-LOAD-FORM-SAVING-SLOTS` Section 31.7.9, “Weak Hash Tables” `EXT:FCASE` `I18N:GETTEXT`
Release 2.29 | 2002-07-25 | bruno
Bug-fix/portability: gcc 3.1 etc
Release 2.30 | 2002-09-15 | sds
Do not bundle GNU libiconv, GNU gettext, GNU readline, GNU libsigsegv. `CHARSET:UCS-4` `CUSTOM:*PARSE-NAMESTRING-DOT-FILE*` `SOCKET:SOCKET-STREAM-SHUTDOWN` `POSIX:STREAM-LOCK`, `POSIX:COPY-FILE`, `POSIX:DUPLICATE-HANDLE` New module: `oracle`
Release 2.31 | 2003-09-01 | sds
Changed bytecode format New modules: `fastcgi`, `dirkey`, `bindings/win32`, `syscalls`, `netica` Support modules on Win32. UNICODE 3.2 New backquote implementation. Many [ANSI CL standard] compliance fixes. More “FFI” functionality.
Release 2.32 | 2003-12-29 | sds
support LFS New modules: `berkeley-db`, `pcre`
Release 2.33 | 2004-03-17 | sds
Changed bytecode format `EXT:MOD-EXPT`, `CUSTOM:*APROPOS-MATCHER*`, `EXT:ARGV`, `GRAY:STREAM-POSITION` `DEFINE-METHOD-COMBINATION` Portability: removed Acorn and Amiga support, fixed UNIXes.
Release 2.33.1 | 2004-05-22 | sds
Bug-fixes, portability: gcc 3.4
Release 2.33.2 | 2004-06-02 | sds
Portability: RedHat Fedora Linux/x86
Release 2.34 | 2005-07-20 | sds
Changed bytecode format Chapter 29, Meta-Object Protocol Section 31.7, “Weak Objects” Section 11.5, “Package Case-Sensitivity” `EXT:SET-GLOBAL-HANDLER`, `EXT:WITHOUT-GLOBAL-HANDLERS` Portability: removed DOS and OS/2 support. New modules: `matlab`, `rawsock`, `zlib`, `i18n`, `pari`.
Release 2.35 | 2005-08-29 | sds
`EXT:COMPILED-FILE-P` `EXT:CHAR-INVERTCASE`, `EXT:STRING-INVERTCASE`, `EXT:NSTRING-INVERTCASE` `POSIX:STREAM-OPTIONS` Close all file descriptors before `exec`.
Release 2.36 | 2005-12-04 | sds
`EXT:OPEN-HTTP`, `EXT:NOTSPECIAL`, `FFI:DEF-C-CONST`, `BASE64` `modules/clx/new-clx/demos/koch.lisp` `src/spvw_sigterm.d`
Release 2.37 | 2006-01-02 | sds
`SOCKET:SOCKET-SERVER` accepts `:INTERFACE` and `:BACKLOG`. Fixed `(`SETF` `EXT:GETENV`)`.
Release 2.38 | 2006-01-24 | sds
`EXT:SAVEINITMEM` creates standalone executables.
Release 2.39 | 2006-07-16 | sds
Reliable stack overflow detection and recovery.
Release 2.40 | 2006-09-23 | sds
Changed bytecode format Keep doc string and lambda list in the closure object.
Release 2.41 | 2006-10-13 | sds
`FFI:DEFAULT-FOREIGN-LIBRARY` New module: `libsvm`
Release 2.42 | 2007-10-16 | sds
Section 8.2, “The structure Meta-Object Protocol” `EXT:RENAME-DIRECTORY` Many additions to `modules/clx/new-clx/demos/` New modules: `gtk2`, `gdbm`
Release 2.43 | 2007-11-18 | sds
The CLISP build process is now in compliance with the GNU standards. Use gnulib-tool to sync with GNU Portability Library.
Release 2.44 | 2008-02-02 | sds
Do not bundle GNU libffcall.
Release 2.44.1 | 2008-02-24 | bruno
Portability: work around gcc bug 34300 present in gcc 4.2 and 4.3.
Release 2.45 | 2008-05-15 | sds
Changed bytecode format Just-In-Time compilation (experimental) via GNU lightning. `FFI:DEF-CALL-OUT` and `FFI:DEF-C-VAR` accept `:VERSION`. read-eval-print loop commands accept arguments. Section 33.2.14, “Standard file input and output”. Fixed cross-compilation.
Release 2.46 | 2008-07-02 | sds
`:WORD-SIZE=64` in `*FEATURES*` on 64-bit platforms. Section 33.2.15, “Error handling”. Macro `XLIB:WITH-OPEN-DISPLAY`. Fixed the remaining bugs in `SPECIAL` bindings in evaluated code on `TYPECODES` platforms.
Release 2.47 | 2008-10-23 | sds
New module: `dbus` `EXT:PROBE-PATHNAME` `EXT:CANONICALIZE` `CUSTOM:*REOPEN-OPEN-FILE*` `POSIX:FILE-SIZE`
Release 2.48 | 2009-07-28 | sds
Thread support (experimental), see Section 32.5, “Multiple Threads of Execution” `POSIX:WAIT` `EXT:TRIM-IF` `src/m4/clisp.m4`
Release 2.49 | 2010-07-07 | sds
`CUSTOM:*USER-LIB-DIRECTORY*`; dynamic modules are now the default build option `-disable-readline` COMPILER-DIAGNOSTICS:USE-HANDLER Updated `pari`

Abstract

This document describes the GNU CLISP - an implementation of the [ANSI CL standard].

See the section called “Bugs” for instructions on how to report bugs (both in the software and the documentaion).

See Q: A.1.1.5 for information on CLISP support.

List of Figures

29.1. Inheritance structure of metaobject classes
29.2. Inheritance structure of class metaobject classes
29.3. Inheritance structure of slot definition metaobject classes
29.4. Inheritance structure of generic function metaobject classes
29.5. Inheritance structure of method metaobject classes
29.6. Inheritance structure of specializer metaobject classes
29.7. Inheritance structure of method combination metaobject classes

List of Tables

1. Mark-up conventions
3.1. Function call limits
12.1. Boolean operations
12.2. Fixnum limits
13.1. Number of characters
13.2. Standard characters
13.3. Semi-standard characters
13.4. Additional Named Characters
13.5. Additional syntax for characters with code from #x00 to #x1F:
13.6. Additional characters (Win32 platform only.)
13.7. Additional characters (UNIX platform only.)
13.8. Character bit constants (obsolete)
15.1. Array limits
19.1. The minimum filename syntax that may be used portably
25.1. Commands common to the main loop, the debugger and the stepper
25.2. Commands common to the debugger and the stepper
25.3. Commands common to the debugger and the stepper
25.4. Commands specific to `EVAL`/`APPLY`
25.5. Commands specific to the debugger
25.6. Commands specific to the stepper
25.7. Time granularity
29.1. Direct Superclass Relationships Among The Specified Metaobject Classes
29.2. Initialization arguments and accessors for class metaobjects
29.3. Initialization arguments and accessors for slot definition metaobjects
29.4. Initialization arguments and accessors for generic function metaobjects
29.5. Initialization arguments and accessors for method metaobjects
29.6. The correspondence between slot access function and underlying slot access generic function
35.1. Memory models with `TYPECODES`
35.2. Memory models with `HEAPCODES`

List of Examples

21.1. Dialog with user using completion
25.1. Identifying Individual Calls in `TRACE`
30.1. Example of `EXT:FILL-STREAM` usage
32.1. Create a module set with GNU libc bindings
32.2. Simple declarations and access
32.3. External C variable and some accesses
32.4. Calling an external function
32.5. Another example for calling an external function
32.6. Accessing cpp macros
32.7. Calling Lisp from C
32.8. Calling Lisp from C dynamically
32.9. Variable size arguments: calling `gethostname` from CLISP
32.10. Accessing variables in shared libraries
32.11. Controlling validity of resources
32.12. Floating point arrays
32.13. Lisp read-eval-print loop server
32.14. Lisp HTTP client
33.1. `REGEXP:MATCH`
33.2. `REGEXP:REGEXP-QUOTE`
33.3. Count unix shell users

# Overview

These notes discuss the CLISP implementation of Common Lisp by Bruno Haible and Michael Stoll. The current maintainers are Bruno Haible and Sam Steingold.

This implementation is mostly conforming to the [ANSI CL standard] available on-line as the [Common Lisp HyperSpec] (but the printed ANSI document remains the authoritative source of information). [ANSI CL standard] supersedes the earlier specifications [CLtL1] and [CLtL2].

The first part of these notes, Part I, “Chapters or the Common Lisp HyperSpec”, is indexed in parallel to the [Common Lisp HyperSpec] and documents how CLISP implements the [ANSI CL standard].

The second part, Part II, “Common Portable Extensions”, documents the common extensions to the [ANSI CL standard], specifically Meta-Object Protocol and “GRAY” `STREAM`s.

The third part, Part III, “Extensions Specific to CLISP”, documents the CLISP-specific extensions, e.g., Section 32.4, “Socket Streams”.

The fourth part, Part IV, “Internals of the CLISP Implementation”, is intended mostly for developers as it documents the CLISP internals, e.g., garbage-collection, adding new built-ins, and the bytecodes generated by the compiler (i.e., what is printed by `DISASSEMBLE`).

# Conventions

The following is the mark-up notations used in this document:

Table 1. Mark-up conventions

Object Kind | Example
--- | ---
Function | `CAR`
Variable | `CUSTOM:*LOAD-PATHS*`
Formal Argument | `x`
Keyword | `:EOF`
Number | `0`
Character | #\Newline
Class, type | `REGEXP:MATCH`
`FORMAT` instruction | `~A`
Standard lambda list keyword | `&KEY`
Declaration | `FTYPE`
Package | “COMMON-LISP-USER”
Real file | `config.lisp`
Abstract file | `#P".c"`
Code (you are likely to type it) | `(`CONS` 1 2)`
Data (CLISP is likely to print it) | `#(1 2 3)`
Program listing |
    (DEFUN cycle-length (n &OPTIONAL (len 1) (top 0))
      (COND ((= n 1) (VALUES len top))
            ((EVENP n) (cycle-length (ASH n -1) (1+ len) (MAX top n)))
            (T (LET ((next (1+ (* 3 n))))
                 (cycle-length next (1+ len) (MAX top next))))))
Bytecode instruction | `(STOREV `k` `m`)`
First mention of an entity | firstterm
External module | `libsvm`, `bindings/glibc`
Command line argument | `-x`
Interaction |
    Computer output
    Prompt: user input

# Part I. Chapters or the [Common Lisp HyperSpec]

## Chapter 1. Introduction [chap-1]

## 1.1. Special Symbols [sec_1-4-1-3]

The final delimiter of an interactive stream:

UNIX
  type Control+D at the beginning of a line
Win32
  type Control+Z, followed by Enter

This final delimiter is never actually seen by programs; no need to test for #\^D or #\^Z - use `READ-CHAR-NO-HANG` to check for `end-of-stream`.

A newline character can be entered by the user by pressing the Enter key.

See also Section 21.13, “Function `CLEAR-INPUT`”.

## 1.2. Error Terminology [sec_1-4-2]

Safety settings are ignored by the interpreted code; therefore where the standard uses the phrase “should signal an error”, an `ERROR` is `SIGNAL`ed. See Section 3.3.5, “Declaration `SAFETY`” for the safety of compiled code.

## 1.3. Symbols in the Package “COMMON-LISP” [sec_1-9]

All 978 symbols in the “COMMON-LISP” package specified by the [ANSI CL standard] are implemented.

## Chapter 2. Syntax [chap-2]

## 2.1. Standard Characters [sec_2-1-3]

The standard characters are #\Newline and the graphic characters with a `CODE-CHAR` between 32 and 126 (inclusive).

## 2.2. Reader Algorithm [sec_2-2]

The requirement of step 4 that a “reader macro function may return zero values or one value” is enforced. You can use the function `VALUES` to control the number of values returned.

## 2.3. Symbols as Tokens [sec_2-3-4]

A reserved token , i.e., a token that has potential number syntax but cannot be interpreted as a `NUMBER`, is interpreted as `SYMBOL` when being read.

## 2.4. Valid Patterns for Tokens [sec_2-3-5]

When a token with package markers is read, then no checking is done whether the `SYMBOL-PACKAGE` part and the `SYMBOL-NAME` part do not have number syntax. (What would the purpose of this check be?) So we consider tokens like USER:: or :1 or LISP::4711 or 21:3 as symbols.

## 2.5. Backquote [sec_2-4-6]

The backquote read macro also works when nested. Example:

       (EVAL ``(,#'(LAMBDA () ',a) ,#'(LAMBDA () ',b)))
     ≡ (EVAL `(list #'(LAMBDA () ',a) #'(LAMBDA () ',b)))
     ≡ (EVAL (list 'list (list 'function (list 'lambda nil (list 'quote a)))
                         (list 'function (list 'lambda nil (list 'quote b)))))

## 2.6. Sharpsign [sec_2-4-8]

Reader macros are also defined for the following:

Additional reader macros

`#,`
  load-time evaluation, kept despite the [ANSI CL standard] issue SHARP-COMMA-CONFUSION:REMOVE.
`#Y`
  compiled `FUNCTION` objects and input `STREAM`'s `EXT:ENCODING`s
`#""`
  `PATHNAME`: `#"test.lisp"` is the value of `(`PATHNAME` "test.lisp")`

### 2.6.1. Sharpsign Backslash [sec_2-4-8-1]

#\Code allows input of characters of arbitrary code: e.g., #\Code231 reads as the character `(`CODE-CHAR` 231)`.

### 2.6.2. Sharpsign Less-Than-Sign [sec_2-4-8-20]

This is the list of objects whose external representation cannot be meaningfully read in:

Unreadable objects

`#<`type` ...>`
  all `STRUCTURE-OBJECT`s lacking a keyword constructor
`#<ARRAY `type` `dimensions`>`
  all `ARRAY`s except `STRING`s, if `*PRINT-ARRAY*` is `NIL`
`#<SYSTEM-FUNCTION `name`>`
  built-in function written in C
`#<ADD-ON-SYSTEM-FUNCTION `name`>`
  module function written in C
`#<SPECIAL-OPERATOR `name`>`
  special operator handler
`#<COMPILED-FUNCTION `name`>`
  compiled function, if `CUSTOM:*PRINT-CLOSURE*` is `NIL`
`#<FUNCTION `name` ...>`
  interpreted function, , if `CUSTOM:*PRINT-CLOSURE*` is `NIL`
`#<FRAME-POINTER #x...>`
  pointer to a stack frame
`#<DISABLED POINTER>`
  frame pointer which has become invalid on exit from the corresponding `BLOCK` or `TAGBODY`
`#<...STREAM...>`
  `STREAM`
`#<PACKAGE `name`>`
  `PACKAGE`
`#<HASH-TABLE #x...>`
  `HASH-TABLE`, if `*PRINT-ARRAY*` is `NIL`
`#<READTABLE #x...>`
  `READTABLE`
`#<SYMBOL-MACRO `form`>`
  `SYMBOL-MACRO` handler
`#<MACRO `function`>`
  macro expander (defined by `DEFMACRO` and friends)
`#<`FFI:FOREIGN-POINTER` #x...>`
  foreign pointer (Platform Dependent: UNIX, Win32 platforms only.)
`#<`FFI:FOREIGN-ADDRESS` #x...>`
  foreign address (Platform Dependent: UNIX, Win32 platforms only.)
`#<`FFI:FOREIGN-VARIABLE` `name` #x...>`
  foreign variable (Platform Dependent: UNIX, Win32 platforms only.)
`#<`FFI:FOREIGN-FUNCTION` `name` #x...>`
  foreign function (Platform Dependent: UNIX, Win32 platforms only.)
`#<UNBOUND>`
  “value” of an unbound symbol, an unsupplied optional or keyword argument
`#<SPECIAL REFERENCE>`
  environment marker for variables declared `SPECIAL`
`#<DOT>`
  internal `READ` result for “.”
`#<END OF FILE>`
  internal `READ` result, when the `end-of-stream` is reached
`#<READ-LABEL ...>`
  intermediate `READ` result for `#n#`
`#<ADDRESS #x...>`
  machine address, should not occur
`#<SYSTEM-POINTER #x...>`
  should not occur

## Chapter 3. Evaluation and Compilation [chap-3]

All the functions built by `FUNCTION`, `COMPILE` and the like are atoms. There are built-in functions written in C, compiled functions (both of type `COMPILED-FUNCTION`) and interpreted functions (of type `FUNCTION`).

Table 3.1. Function call limits

`CALL-ARGUMENTS-LIMIT` | 212=4096
`MULTIPLE-VALUES-LIMIT` | 27=128
`LAMBDA-PARAMETERS-LIMIT` | 212=4096

## 3.1. Evaluation [sec_3-1]

### 3.1.1. Introduction to Environments [sec_3-1-1]

Macro `EXT:THE-ENVIRONMENT`. As in Scheme, the macro `(`EXT:THE-ENVIRONMENT`)` returns the current lexical environment. This works only in interpreted code and is not compilable!

Function `(EXT:EVAL-ENV `form` `&OPTIONAL` `environment`)`. evaluates a form in a given lexical environment, just as if the form had been a part of the program that the `environment` came from.

### 3.1.2. Symbols as Forms [sec_3-1-2-1-1]

#### 3.1.2.1. Macro `DEFINE-SYMBOL-MACRO`

The macro `DEFINE-SYMBOL-MACRO` establishes `SYMBOL-MACRO`s with global scope (as opposed to `SYMBOL-MACRO`s defined with `SYMBOL-MACROLET`, which have local scope).

The function `EXT:SYMBOL-MACRO-EXPAND` tests for a `SYMBOL-MACRO`: If `symbol` is defined as a `SYMBOL-MACRO` in the global environment, `(`EXT:SYMBOL-MACRO-EXPAND` `symbol`)` returns two values, `T` and the expansion; otherwise it returns `NIL`.

`EXT:SYMBOL-MACRO-EXPAND` is a special case of `MACROEXPAND-1`. `MACROEXPAND-1` can also test whether a symbol is defined as a `SYMBOL-MACRO` in lexical environments other than the global environment.

#### 3.1.2.2. Dynamic Variables [sec_3-1-2-1-1-2]

“Undefined variables”, i.e. variables which are referenced outside any lexical binding for a variable of the same name and which are not declared `SPECIAL`, are treated like dynamic variables in the global environment. The compiler `SIGNAL`s a `WARNING` when it encounters an undefined variable.

### 3.1.3. Conses as Forms [sec_3-1-2-1-2]

Lists of the form `((`SETF` `symbol`) ...)` are also treated as function forms. This makes the syntax `(`function-name` `arguments` ...)` consistent with the syntax `(`FUNCALL` #'`function-name` `arguments` ...)`. It implements the item 7 of the [ANSI CL standard] issue FUNCTION-NAME:LARGE and the definition of function forms, and is consistent with the use of function names elsewhere in Common Lisp.

### 3.1.4. Special Forms [sec_3-1-2-1-2-1]

#### 3.1.4.1. Special operator `EVAL-WHEN`

`EVAL-WHEN` also accepts the situations `(NOT EVAL)` and `(NOT COMPILE)`.

### Warning

The situations `EVAL`, `LOAD` and `COMPILE` are deprecated by the [ANSI CL standard], and they are not equivalent to the new standard situations `:EXECUTE`, `:LOAD-TOPLEVEL` and `:COMPILE-TOPLEVEL` in that they ignore the top-level form versus non-top-level form distinction.

#### 3.1.4.2. Special operator `THE`

The special form `(`THE` `value-type` `form`)` is similar to `CHECK-TYPE` but does a type check only in interpreted code (no type check is done in compiled code - but see the `EXT:ETHE` macro) and does not allow interactive error correction by the user.

### 3.1.5. Function Forms [sec_3-1-2-1-2-3]

Constant `LAMBDA-LIST-KEYWORDS`. `(`&OPTIONAL` `&REST` `&KEY` `&ALLOW-OTHER-KEYS` `&AUX` `&BODY` `&WHOLE` `&ENVIRONMENT`)`

#### 3.1.5.1. Function `SYMBOL-FUNCTION`

`(`SETF` (`SYMBOL-FUNCTION` `symbol`) `object`)` requires `object` to be either a `FUNCTION`, a `SYMBOL-FUNCTION` return value, or a lambda expression. The lambda expression is thereby immediately converted to a `FUNCTION`.

### 3.1.6. Macros `DEFUN` & `DEFMACRO`

`DEFUN` and `DEFMACRO` are allowed in non-toplevel positions. As an example, consider the old ([CLtL1]) definition of `GENSYM`:

    (let ((gensym-prefix "G")
          (gensym-count 1))
      (defun gensym (&optional (x nil s))
        (when s
          (cond ((stringp x) (setq gensym-prefix x))
                ((integerp x)
                 (if (minusp x)
                   (error "~S: index ~S is negative" 'gensym x)
                   (setq gensym-count x)))
                (t (error "~S: argument ~S of wrong type" 'gensym x))))
        (prog1
          (make-symbol
            (concatenate 'string
              gensym-prefix
              (write-to-string gensym-count :base 10 :radix nil)))
          (incf gensym-count))))

See also Section 3.2.2.2, “Minimal Compilation sec_3-2-2-2”.

Function `EXT:ARGLIST`. Function `(`EXT:ARGLIST` `name`)` returns the lambda list of the function or macro that `name` names and `SIGNAL`s an `ERROR` if `name` is not `FBOUNDP`. It also `SIGNAL`s an `ERROR` when the macro lambda list is not available due to the compiler optimization settings (see Section 3.3.7, “Declaration `SPACE`”).

Variable `CUSTOM:*SUPPRESS-CHECK-REDEFINITION*`. When `CUSTOM:*SUPPRESS-CHECK-REDEFINITION*` is `NIL`, CLISP issues a `STYLE-WARNING` when a function (macro, variable, class, etc) is redefined in a different file than its original definition. It is not a good idea to set this variable to `T`.

Variable `CUSTOM:*DEFUN-ACCEPT-SPECIALIZED-LAMBDA-LIST*`. When `CUSTOM:*DEFUN-ACCEPT-SPECIALIZED-LAMBDA-LIST*` is non-`NIL`, `DEFUN` accepts specialized lambda lists, converting type-parameter associations to type declarations:

    (defun f ((x list) (y integer)) ...)

is equivalent to

    (defun f (x y) (declare (type list x) (type integer y)) ...)

This extension is disabled by `-ansi` and by setting `CUSTOM:*ANSI*` to `T`, but can be re-enabled by setting `CUSTOM:*DEFUN-ACCEPT-SPECIALIZED-LAMBDA-LIST*` explicitly.

## 3.2. Compilation [sec_3-2]

### 3.2.1. Compiler Terminology [sec_3-2-1]

CLISP compiles to platform-independent bytecode.

#### 3.2.1.1. Just-In-Time Native Compilation

##### Platform Dependent: Only in CLISP built with GNU lightning

The code compiled to bytecodes with optimization levels

    (OR (>= 0 SPACE) (<= 1 SPEED))

(by `COMPILE`, `COMPILE-FILE`, or `(COMPILE)`) will be just-in-time (i.e., on the first execution) compiled to native code using GNU lightning.

### 3.2.2. Compilation Semantics [sec_3-2-2]

#### 3.2.2.1. Compiler Macros [sec_3-2-2-1]

Compiler macros are expanded in the compiled code only, and ignored by the interpreter.

#### 3.2.2.2. Minimal Compilation [sec_3-2-2-2]

When a `DEFUN` form is `EVAL`uated, the macros used there are expanded, so they must be already defined, and their (re)definition does not affect functions which are already defined.

This means that even the interpreted code is minimally compiled in CLISP.

#### 3.2.2.3. Semantic Constraints [sec_3-2-2-3]

Non-conforming code that does not follow the rule

> “Special proclamations for dynamic variables must be made in the compilation environment.”

can produce quite unexpected results, e.g., observable differences between compiled and interpreted programs:

    (defun adder-c (value) (declare (COMPILE)) (lambda (x) (+ x value)))
    ⇒ ADDER-C	; compiled function; value is lexical
    (defun adder-i (value) (lambda (x) (+ x value)))
    ⇒ ADDER-I	; interpreted function; value is lexical
    (defparameter add-c-10 (adder-c 10))
    ⇒ ADD-C-10	; compiled function
    (defparameter add-i-10 (adder-i 10))
    ⇒ ADD-I-10	; interpreted function
    (funcall add-c-10 32)
    ⇒ 42	; as expected
    (funcall add-i-10 32)
    ⇒ 42	; as expected
    (defvar value 12)
    ⇒ VALUE	; affects ADDER-I and ADD-I-10 but not ADDER-C and ADD-C-10
    (funcall add-c-10 32)
    ⇒ 42	; as before
    (funcall add-i-10 32)
    ⇒ 44	; value is now dynamic!

Non-conformance. The code shown above has a `SPECIAL` proclamation (by `DEFVAR`) for the variable `value` in the execution environment (before the last two `FUNCALL`s) but not in the compilation environment: at the moment the `ADDER-I` function is defined, `value` is not known to be a `SPECIAL` variable. Therefore the code is not conforming.

##### Rationale

The function `ADD-C-10` was compiled before `value` was declared `SPECIAL`, so the symbol `value` was eliminated from its code and the `SPECIAL` declaration did not affect the return value (i.e., `(funcall add-c-10 32)` always returned 42).

On the opposite, function `ADDER-I` was not compiled, so `ADD-I-10` was interpreted. Whenever `ADD-I-10` is executed, its definition is interpreted all over again. Before `DEFVAR`, `value` is evaluated as a lexical (because it is not declared `SPECIAL` yet), but after `DEFVAR`, we see a globally `SPECIAL` symbol `value` which can have only a global `SYMBOL-VALUE` (not a local binding), and thus we are compelled to evaluate it to 12.

This behavior was implemented intentionally to ease interactive development, because usually the `ADDER-I` above would be followed by a (forgotten) `DEFVAR`.

When a user compiles a program, the compiler is allowed to remember the information whether a variable was `SPECIAL` or not, because that allows the compiler to generate more efficient code, but in interpreted code, when the user changes the state of a variable, he does not want to re-evaluate all `DEFUN`s that use the variable.

[ANSI CL standard] gives the implementation freedom regarding interpreted evaluation, how much it wants to remember / cache, and how much it wants to re-evaluate according the current environment, if it has changed. CLISP implements ad-hoc look-up for variables (but not for macros, see Section 3.2.2.2, “Minimal Compilation sec_3-2-2-2”).

### 3.2.3. Definition of Similarity [sec_3-2-4-2-2]

Hash tables are externalizable objects.

### 3.2.4. Exceptional Situations in the Compiler [sec_3-2-5]

Both `COMPILE` and `EVAL` may `SIGNAL` the `EXT:SOURCE-PROGRAM-ERROR` `CONDITION` which derives from `PROGRAM-ERROR` and which contains additional slots with accessors

`EXT:SOURCE-PROGRAM-ERROR-FORM`
  Returns the whole form in which the `ERROR` was `SIGNAL`ed
`EXT:SOURCE-PROGRAM-ERROR-DETAIL`
  Returns the specific (usually small) part of the above which triggered the `ERROR`

Mixing `&OPTIONAL` and `&KEY`. It is a bad design to have both `&OPTIONAL` and `&KEY` in the same lambda list, especially if the number of optional arguments is even: the users will often forget to supply optional arguments when supplying keys, e.g., `(`READ-FROM-STRING` `string` `:START` 5)` instead of `(`READ-FROM-STRING` `string` t nil `:START` 5)`. This is why the CLISP compiler issues a `STYLE-WARNING` in such cases:

    (DEFUN foo (&OPTIONAL a &KEY b) (cons a b))
    (COMPILE 'foo)
    WARNING: in FOO : Mixing &OPTIONAL and &KEY in lambda list (&OPTIONAL A &KEY B) is bad design
    FOO ;
    1 ;
    NIL

## 3.3. Declarations [sec_3-3]

### 3.3.1. Minimal Declaration Processing Requirements [sec_3-3-1]

The declaration `(`DYNAMIC-EXTENT` `variable` ...)` is ignored.

The type declarations `(`TYPE` `type` `variable` ...)` and `(`FTYPE` `type` `function` ...)` are ignored by both the interpreter and the compiler. Use `CHECK-TYPE` to force type checks.

Rationale. When these declarations lie and a compiler respects them, the generated code often results in a hard crash (segmentation fault).

### 3.3.2. Declaration `SPECIAL`

Declaration `EXT:NOTSPECIAL`. Declarations `(`PROCLAIM` '(`SPECIAL` `variable`))` and `DEFCONSTANT` are undone by the `(`PROCLAIM` '(`EXT:NOTSPECIAL` `variable`))` declaration. This declaration can be used only in global `PROCLAIM` and `DECLAIM` forms, not in local `DECLARE` forms.

### Warning

You cannot expect miracles: functions compiled before the `EXT:NOTSPECIAL` proclamation was issued will still be treating `variable` as special even after the `EXT:NOTSPECIAL` proclamation. See also Section 3.2.2.3, “Semantic Constraints sec_3-2-2-3”.

Function `EXT:SPECIAL-VARIABLE-P`. You can use the function `(`EXT:SPECIAL-VARIABLE-P` `symbol` `&OPTIONAL` `environment`)` to check whether the `symbol` is a dynamic variable. `environment` of `NIL` or omitted means use the global environment. You can also obtain the current lexical environment using the macro `EXT:THE-ENVIRONMENT` (interpreted code only). This function will always return `T` for global special variables and constant variables.

### 3.3.3. Declaration `EXT:CONSTANT-NOTINLINE`

Constants defined by `DEFCONSTANT` but proclaimed `EXT:CONSTANT-NOTINLINE` will not be inlined by the compiler. This is useful for variables which remain constant within an a single Lisp process but may vary between processes and machines (such as endianness or word size) thus they should be written to `#P".fas"`s as symbols, not values.

### 3.3.4. Function `CONSTANTP`

Function `CONSTANTP` fully complies with [ANSI CL standard]. Additionally, some non-trivial forms are identified as constants, e.g., `(`CONSTANTP` '(`+` 1 2 3))` returns `T`.

### Warning

Since `DEFCONSTANT` initial value forms are not evaluated at compile time, `CONSTANTP` will not report `T` of their name within the same compilation unit for the null lexical environment. This is consistent and matches questionable code using the pattern `(`IF` (`CONSTANTP` `form`) (`EVAL` `form`))`. Use `EVAL-WHEN` if you need recognition and the value during compile-time. See also Section 31.11.5, “Macro `EXT:COMPILE-TIME-VALUE`”.

### 3.3.5. Declaration `SAFETY`

Declaration `(`OPTIMIZE` (`SAFETY` 3))` results in “safe” compiled code: function calls are never eliminated. This guarantees the semantics described in [sec_3-5].

### 3.3.6. Declaration `(COMPILE)`

The declaration `(COMPILE)` has the effect that the current form is compiled prior to execution. Examples:

    (LOCALLY (DECLARE (compile)) form)

executes the compiled version of `form`.

    (LET ((x 0))
      (FLET ((inc () (DECLARE (compile)) (INCF x))
             (dec () (DECF x)))
        (VALUES #'inc #'dec)))

returns two functions. The first is compiled and increments `x`, the second is interpreted (slower) and decrements the same `x`.

This declaration can also be used to name the resulting compiled closure:

    (LAMBDA (x) (DECLARE (compile ident)) x)
    ⇒ #<COMPILED-FUNCTION IDENT>
    (FUNCTION-LAMBDA-EXPRESSION *)
    ⇒ NIL	; source is not preserved
    ⇒ T
    ⇒ IDENT
    (FBOUNDP 'ident)
    ⇒ NIL	; sic!

### Note

The declaration `(COMPILE)` is ignored by the following special operators:

`LABELS`
`FLET`
`MACROLET`

### 3.3.7. Declaration `SPACE`

The declaration determines what metadata is recorded in the function object:

`SPACE` `>=` 2
  documentation string is discarded
`SPACE` `>=` 3
  the original lambda list is also discarded (most information is still available, see `DESCRIBE`, but the names of the positional arguments are not).

## 3.4. Lambda Lists [sec_3-4]

### 3.4.1. Boa Lambda Lists [sec_3-4-6]

The initial value of an `&AUX` variable in a boa lambda list is the value of the corresponding slot's initial form.

## Chapter 4. Types and Classes [chap-4]

## 4.1. Types [sec_4-2]

### 4.1.1. Type Specifiers [sec_4-2-3]

The general form of the `COMPLEX` type specifier is `(`COMPLEX` `type-of-real-part` `type-of-imaginary-part`)`. The type specifier `(`COMPLEX` `type`)` is equivalent to `(`COMPLEX` `type` `type`)`.

`DEFTYPE` lambda lists are subject to destructuring (nested lambda lists are allowed, as in `DEFMACRO`) and may contain a `&WHOLE` marker, but not an `&ENVIRONMENT` marker.

Function `(`EXT:TYPE-EXPAND` `type` `&OPTIONAL` `once-p`)`. If `type` is a user-defined type specifier this will expand it recursively until it is no longer a user-defined type (unless `once-p` is supplied and non-`NIL`). Two values are returned - the expansion and an indicator (`T` or `NIL`) of whether the original `type` was a user-defined type specifier.

The possible results of `TYPE-OF`

- `CONS`
- `SYMBOL`, `NULL`, `BOOLEAN`, `KEYWORD`
- `BIT`, `(`INTEGER` 0 `#.``MOST-POSITIVE-FIXNUM`)`, `(`INTEGER` `#.``MOST-NEGATIVE-FIXNUM` (0))`, `(`INTEGER` (`#.``MOST-POSITIVE-FIXNUM`))`, `(`INTEGER` * (`#.``MOST-NEGATIVE-FIXNUM`))`
- `RATIONAL`, `SHORT-FLOAT`, `SINGLE-FLOAT`, `DOUBLE-FLOAT`, `LONG-FLOAT`, `COMPLEX`
- `CHARACTER`, `BASE-CHAR`, `STANDARD-CHAR`
- `(`ARRAY` `element-type` `dimensions`)`, `(`SIMPLE-ARRAY` `element-type` `dimensions`)`
- `(`VECTOR` `T` `size`)`, `(`SIMPLE-VECTOR` `size`)`
- `(`STRING` `size`)`, `(`SIMPLE-STRING` `size`)`
- `(`BASE-STRING` `size`)`, `(`SIMPLE-BASE-STRING` `size`)`
- `(`BIT-VECTOR` `size`)`, `(`SIMPLE-BIT-VECTOR` `size`)`
- `FUNCTION`, `COMPILED-FUNCTION`, `STANDARD-GENERIC-FUNCTION`
- `STREAM`, `FILE-STREAM`, `SYNONYM-STREAM`, `BROADCAST-STREAM`, `CONCATENATED-STREAM`, `TWO-WAY-STREAM`, `ECHO-STREAM`, `STRING-STREAM`
- `PACKAGE`, `HASH-TABLE`, `READTABLE`, `PATHNAME`, `LOGICAL-PATHNAME`, `RANDOM-STATE`, BYTE
- `SPECIAL-OPERATOR`, `LOAD-TIME-EVAL`, `SYMBOL-MACRO`, `GLOBAL-SYMBOL-MACRO`, `EXT:ENCODING`, `FFI:FOREIGN-POINTER`, `FFI:FOREIGN-ADDRESS`, `FFI:FOREIGN-VARIABLE`, `FFI:FOREIGN-FUNCTION`
- `EXT:WEAK-POINTER`, `EXT:WEAK-LIST`, `EXT:WEAK-AND-RELATION`, `EXT:WEAK-OR-RELATION`, `EXT:WEAK-MAPPING`, `EXT:WEAK-AND-MAPPING`, `EXT:WEAK-OR-MAPPING`, `EXT:WEAK-ALIST`, `READ-LABEL`, `FRAME-POINTER`, `SYSTEM-INTERNAL`
- `ADDRESS` (should not occur)
- any other `SYMBOL` (structure types or CLOS classes)
- a class object (CLOS classes without a proper name)

Function `COERCE`. `FIXNUM` is not a character designator in [ANSI CL standard], although `CODE-CHAR` provides an obvious venue to `COERCE` a `FIXNUM` to a `CHARACTER`. When `CUSTOM:*COERCE-FIXNUM-CHAR-ANSI*` is `NIL`, CLISP `COERCE`s `FIXNUM`s to `CHARACTER`s via `CODE-CHAR`. When `CUSTOM:*COERCE-FIXNUM-CHAR-ANSI*` is non-`NIL`, `FIXNUM`s cannot be `COERCE`d to `CHARACTER`s.

## 4.2. Classes [sec_4-3]

The CLOS symbols are `EXPORT`ed from the package “CLOS”. “COMMON-LISP” uses (as in `USE-PACKAGE`) “CLOS” and `EXT:RE-EXPORT`s the [ANSI CL standard] standard exported symbols (the CLISP extensions, e.g., those described in Chapter 29, Meta-Object Protocol, are not `EXT:RE-EXPORT`ed). Since the default `:USE` argument to `MAKE-PACKAGE` is “COMMON-LISP”, the standard CLOS symbols are normally visible in all user-defined packages. If you do not want them (for example, if you want to use the PCL implementation of CLOS instead of the native one), do the following:

    (DEFPACKAGE "CL-NO-CLOS" (:use "CL"))
    (DO-EXTERNAL-SYMBOLS (symbol “COMMON-LISP”)
      (SHADOW symbol "CL-NO-CLOS"))
    (DO-SYMBOLS (symbol "CL-NO-CLOS")
      (EXPORT symbol "CL-NO-CLOS"))
    (IN-PACKAGE "CL-NO-CLOS")
    (LOAD "pcl")	; or whatever
    (DEFPACKAGE "MY-USER" (:use "CL-NO-CLOS"))
    (IN-PACKAGE "MY-USER")
    ;; your code which uses PCL goes here

## 4.3. Deviations from [ANSI CL standard]

`DEFCLASS` supports the option `:METACLASS` `STRUCTURE-CLASS`. This option is necessary in order to define a subclass of a `DEFSTRUCT`-defined structure type using `DEFCLASS` instead of `DEFSTRUCT`.

When `CALL-NEXT-METHOD` is called with arguments, the rule that the ordered set of applicable methods must be the same as for the original arguments is enforced by the implementation only in interpreted code.

`CLOS:GENERIC-FLET` and `CLOS:GENERIC-LABELS` are implemented as macros, not as special operators (as permitted by [sec_3-1-2-1-2-2]). They are not imported into the packages “COMMON-LISP-USER” and “COMMON-LISP” because of the [ANSI CL standard] issue GENERIC-FLET-POORLY-DESIGNED:DELETE.

`PRINT-OBJECT` is only called on objects of type `STANDARD-OBJECT` and `STRUCTURE-OBJECT`. It is not called on other objects, like `CONS`es and `NUMBER`s, due to the performance concerns.

## 4.4. Standard Metaclasses [sec_4-3-1-1]

Among those classes listed in Figure 4-8, only the following are instances of `BUILT-IN-CLASS`:

- `T`
- `CHARACTER`
- `NUMBER`, `COMPLEX`, `REAL`, `FLOAT`, `RATIONAL`, `RATIO`, `INTEGER`
- `SEQUENCE`
- `ARRAY`, `VECTOR`, `BIT-VECTOR`, `STRING`
- `LIST`, `CONS`
- `SYMBOL`, `NULL`
- `FUNCTION`
- `HASH-TABLE`
- `PACKAGE`
- `PATHNAME`, `LOGICAL-PATHNAME`
- `RANDOM-STATE`
- `READTABLE`
- `STREAM`, `BROADCAST-STREAM`, `CONCATENATED-STREAM`, `ECHO-STREAM`, `STRING-STREAM`, `FILE-STREAM`, `SYNONYM-STREAM`, `TWO-WAY-STREAM`

## 4.5. Defining Classes [sec_4-3-2]

`DEFCLASS` supports the `:METACLASS` option. Possible values are `STANDARD-CLASS` (the default), `STRUCTURE-CLASS` (which creates structure classes, like `DEFSTRUCT` does), and user-defined meta-classes (see Section 29.3.6.7, “Generic Function `CLOS:VALIDATE-SUPERCLASS`”).

It is not required that the superclasses of a class are defined before the `DEFCLASS` form for the class is evaluated. Use Meta-Object Protocol generic functions `CLOS:CLASS-FINALIZED-P` to check whether the class has been finalized and thus its instances can be created, and `CLOS:FINALIZE-INHERITANCE` to force class finalization.

See also Section 29.3.1, “Macro `DEFCLASS`”.

## 4.6. Redefining Classes [sec_4-3-6]

Trivial changes, e.g., those that can occur when doubly loading the same code, do not require updating the instances. These are the changes that do not modify the set of local slots accessible in instances, e.g., changes to slot options `:INITFORM`, `:DOCUMENTATION`, and changes to class options `:DEFAULT-INITARGS`, `:DOCUMENTATION`.

The instances are updated when they are first accessed, not at the time when the class is redefined or `MAKE-INSTANCES-OBSOLETE` is called. When the class has been redefined several times since the instance was last accessed, `UPDATE-INSTANCE-FOR-REDEFINED-CLASS` is still called just once.

## Chapter 5. Data and Control Flow [chap-5]

## 5.1. Generalized Reference [sec_5-1]

`&KEY` markers in `DEFSETF` lambda lists are supported, but the corresponding keywords must appear literally in the program text.

An attempt to modify read-only data `SIGNAL`s an `ERROR`. Program text and quoted constants loaded from files are considered read-only data. This check is only performed for strings, not for conses, other kinds of arrays, and user-defined data types.

See also Section 31.11.2, “Macros `EXT:LETF` & `EXT:LETF*`”.

## 5.2. Setf Expansions [sec_5-1-1-2]

`(`GET-SETF-EXPANSION` `form` `&OPTIONAL` `environment`)`, `(EXT:GET-SETF-METHOD `form` `&OPTIONAL` `environment`)`, and `(EXT:GET-SETF-METHOD-MULTIPLE-VALUE `form` `&OPTIONAL` `environment`)` receive as optional argument `environment` the environment necessary for macro expansions. In `DEFINE-SETF-EXPANDER` and `EXT:DEFINE-SETF-METHOD` lambda lists, one can specify `&ENVIRONMENT` and a variable, which will be bound to the environment. This environment should be passed to all calls of `GET-SETF-EXPANSION`, `EXT:GET-SETF-METHOD` and `EXT:GET-SETF-METHOD-MULTIPLE-VALUE`. If this is done, even local macros will be interpreted as places correctly.

## 5.3. Kinds of Places [sec_5-1-2]

Additional places:

`FUNCALL`
  `(`SETF` (`FUNCALL` #'`symbol` ...) `object`)` and `(`SETF` (`FUNCALL` '`symbol` ...) `object`)` are equivalent to `(`SETF` (`symbol` ...) `object`)`.
`PROGN`
  `(`SETF` (`PROGN` `form` ... `place`) `object`)`
`LOCALLY`
  `(`SETF` (`LOCALLY` `declaration` ... `form` ... `place`) `object`)`
`IF`
  `(`SETF` (`IF` `condition` `place1` `place2`) `object`)`
`GET-DISPATCH-MACRO-CHARACTER`
  `(`SETF` (`GET-DISPATCH-MACRO-CHARACTER` ...) ...)` calls `SET-DISPATCH-MACRO-CHARACTER`.
`EXT:LONG-FLOAT-DIGITS`:
  `(`SETF` (`EXT:LONG-FLOAT-DIGITS`) `digits`)` sets the default mantissa length of `LONG-FLOAT`s to `digits` bits.
`VALUES-LIST`

  `(`SETF` (`VALUES-LIST` `list`) `form`)` is equivalent to `(`VALUES-LIST` (`SETF` `list` (`MULTIPLE-VALUE-LIST` `form`)))`.

  ### Note

  Note that this place is restricted: it can only be used in `SETF`, `EXT:LETF`, `EXT:LETF*`, not in other positions.

## 5.4. Miscellaneous

### Function `FUNCTION-LAMBDA-EXPRESSION`

The `name` of a `FFI:FOREIGN-FUNCTION` is a string (the name of the underlying C function), not a lisp function name.

### Macro `DESTRUCTURING-BIND`

This macro does not perform full error checking.

### Macros `PROG1`, `PROG2`, `AND`, `OR`, `PSETQ`, `WHEN`, `UNLESS`, `COND`, `CASE`, `MULTIPLE-VALUE-LIST`, `MULTIPLE-VALUE-BIND`, `MULTIPLE-VALUE-SETQ`

These macros are implemented as special operators (as permitted by [sec_3-1-2-1-2-2]) and, as such, are rather efficient.

## 5.5. Macro `DEFCONSTANT`

The initial value is not evaluated at compile time, just like with `DEFVAR` and `DEFPARAMETER`. Use `EVAL-WHEN` if you need the value at compile time.

constant variables may not be bound dynamically or lexically.

See also Section 3.3.3, “Declaration `EXT:CONSTANT-NOTINLINE`”.

If you need to undo the effects of a `DEFCONSTANT` form, `PROCLAIM` the symbol `SPECIAL` (to turn the constant variable into a dynamic variable), and then `PROCLAIM` it `EXT:NOTSPECIAL` (to turn the dynamic variable into a lexical variable).

### Note

If you follow the usual variable naming convention (`*FOO*` for `DEFVAR` and `DEFPARAMETER`, `+BAR+` for `DEFCONSTANT`, `ZOT` for `LET`/`LET*`), you will save yourself a lot of trouble. See also Q: A.4.14.

### 5.5.1. Variable `CUSTOM:*SUPPRESS-SIMILAR-CONSTANT-REDEFINITION-WARNING*`

If the variable being defined by `DEFCONSTANT` is already bound to a value which is not `EQL` to the new value, a `WARNING` is issued. If, however, the new value is visually similar (prints to the same string, as is commonly the case when re-loading files) to the old one, the warning can be suppressed by setting `CUSTOM:*SUPPRESS-SIMILAR-CONSTANT-REDEFINITION-WARNING*` to a non-`NIL` value.

The initial value of `CUSTOM:*SUPPRESS-SIMILAR-CONSTANT-REDEFINITION-WARNING*` is `NIL`.

## 5.6. Macro `EXT:FCASE`

This macro allows specifying the test for `CASE`, e.g.,

    (fcase string= (subseq foo 0 (position #\Space foo))
      ("first" 1)
      (("second" "two") 2)
      (("true" "yes") t)
      (otherwise nil))

is the same as

    (let ((var (subseq foo 0 (position #\Space foo))))
      (cond ((string= var "first") 1)
            ((or (string= var "second") (string= var "two")) 2)
            ((or (string= var "true") (string= var "yes")) t)
            (t nil)))

If you use a built-in `HASH-TABLE` test (see Section 18.4, “Function `HASH-TABLE-TEST`”) as the test (e.g., `EQUAL` instead of `STRING=` above, but not a test defined using `EXT:DEFINE-HASH-TABLE-TEST`), the compiler will be able to optimize the `EXT:FCASE` form better than the corresponding `COND` form.

## 5.7. Function `EXT:XOR`

This function checks that exactly one of its arguments is non-`NIL` and, if this is the case, returns its value and index in the argument list as multiple values, otherwise returns `NIL`.

## 5.8. Function `EQ`

`EQ` compares `CHARACTER`s and `FIXNUM`s as `EQL` does. No unnecessary copies are made of `CHARACTER`s and `NUMBER`s. Nevertheless, one should use `EQL` as it is more portable across Common Lisp implementations.

`(`LET` ((`x` `y`)) (`EQ` `x` `x`))` always returns `T` for any Lisp object `y`. See also Equality of foreign values.

## 5.9. Special Operator `FUNCTION`

`(`FUNCTION` `symbol`)` returns the local function definition established by `FLET` or `LABELS`, if it exists, otherwise the global function definition.

`(`SPECIAL-OPERATOR-P` `symbol`)` returns `NIL` or `T`. If it returns `T`, then `(`SYMBOL-FUNCTION` `symbol`)` returns the (useless) special operator handler.

## Chapter 6. Iteration [chap-6]

## 6.1. The LOOP Facility [sec_6-1]

### 6.1.1. Mixing Termination Test Clauses [sec_6-1-4]

Mixing termination test clauses with different default return values is not allowed because it is not specifed whether

    (loop repeat 1 thereis nil never nil)

should return `T` (the default return value from `NEVER`) of `NIL` (the default return value from `THEREIS`).

### 6.1.2. Iteration variables in the loop epilogue

The standard is unambiguous in that the iteration variables do still exist in the `FINALLY` clause, but not as to what values these variables might have. Therefore the code which relies on the values of such variables, e.g.,

    (loop for x on y finally (return x))

is inherently non-portable across Common Lisp implementations, and should be avoided.

### 6.1.3. Backward Compatibility

There have been some tightening in the `LOOP` syntax between [CLtL2] and [ANSI CL standard], e.g., the following form is legal in the former but not the latter:

    (loop initially for i from 1 to 5 do (print i) finally return i)

When `CUSTOM:*LOOP-ANSI*` is `NIL`, such forms are still accepted in CLISP but elicit a warning at macro-expansion time. When `CUSTOM:*LOOP-ANSI*` is non-`NIL`, an `ERROR` is `SIGNAL`ed.

## 6.2. Miscellaneous

The macros `DOLIST` and `DOTIMES` establish a single binding for the iteration variable and assign it on each iteration.

## Chapter 7. Objects [chap-7]

## 7.1. Standard Method Combination [sec_7-6-6-2]

Generic function `CLOS:NO-PRIMARY-METHOD` (similar to `NO-APPLICABLE-METHOD`) is called when there is an applicable method but no applicable primary method.

The default methods for `CLOS:NO-PRIMARY-METHOD`, `NO-APPLICABLE-METHOD` and `NO-NEXT-METHOD` `SIGNAL` an `ERROR` of type `CLOS:METHOD-CALL-ERROR` . You can find out more information about the error using functions `CLOS:METHOD-CALL-ERROR-GENERIC-FUNCTION`, `CLOS:METHOD-CALL-ERROR-ARGUMENT-LIST`, and (only for `NO-NEXT-METHOD`) `CLOS:METHOD-CALL-ERROR-METHOD`. Moreover, when the generic function has only one dispatching argument, (i.e., such an argument that not all the corresponding parameter specializers are `T`), an `ERROR` of type `CLOS:METHOD-CALL-TYPE-ERROR` is `SIGNAL`ed, additionally making `TYPE-ERROR-DATUM` and `TYPE-ERROR-EXPECTED-TYPE` available.

## Chapter 8. Structures [chap-8]

## 8.1. The options for `DEFSTRUCT`

### 8.1.1. The `:PRINT-FUNCTION` option

The `:PRINT-FUNCTION` option should contain a lambda expression `(`LAMBDA` (object stream depth) (declare (ignore depth)) ...)` This lambda expression names a `FUNCTION` whose task is to output the external representation of the `STRUCTURE-OBJECT` `object` onto the `STREAM` `stream`. This may be done by outputting text onto the stream using `WRITE-CHAR`, `WRITE-STRING`, `WRITE`, `PRIN1`, `PRINC`, `PRINT`, `PPRINT`, `FORMAT` and the like. The following rules must be obeyed:

- The value of `*PRINT-ESCAPE*` must be respected.
- The treatment of `*PRINT-PRETTY*` is up to you.
- The value of `*PRINT-CIRCLE*` need not be respected. This is managed by the system. (But the print-circle mechanism handles only those objects that are direct or indirect components of the structure.)
- The value of `*PRINT-LEVEL*` is respected by `WRITE`, `PRIN1`, `PRINC`, `PRINT`, `PPRINT`, `FORMAT` instructions `~A`, `~S`, `~W`, and `FORMAT` instructions `~R`, `~D`, `~B`, `~O`, `~X`, `~F`, `~E`, `~G`, `~$` with not-numerical arguments. Therefore the print-level mechanism works automatically if only these functions are used for outputting objects and if they are not called on objects with nesting level > 1. (The print-level mechanism does not recognize how many parentheses you have output. It only counts how many times it was called recursively.)
- The value of `*PRINT-LENGTH*` must be respected, especially if you are outputting an arbitrary number of components.
- The value of `*PRINT-READABLY*` must be respected. Remember that the values of `*PRINT-ESCAPE*`, `*PRINT-LEVEL*`, `*PRINT-LENGTH*` are ignored if `*PRINT-READABLY*` is true. The value of `*PRINT-READABLY*` is respected by `PRINT-UNREADABLE-OBJECT`, `WRITE`, `PRIN1`, `PRINC`, `PRINT`, `PPRINT`, `FORMAT` instructions `~A`, `~S`, `~W`, and `FORMAT` instructions `~R`, `~D`, `~B`, `~O`, `~X`, `~F`, `~E`, `~G`, `~$` with not-numerical arguments. Therefore `*PRINT-READABLY*` will be respected automatically if only these functions are used for printing objects.
- You need not worry about the values of `*PRINT-BASE*`, `*PRINT-RADIX*`, `*PRINT-CASE*`, `*PRINT-GENSYM*`, `*PRINT-ARRAY*`, `CUSTOM:*PRINT-CLOSURE*`, `CUSTOM:*PRINT-RPARS*`, `CUSTOM:*PRINT-INDENT-LISTS*`.

### 8.1.2. The `:INHERIT` option

The `:INHERIT` option is exactly like `:INCLUDE` except that it does not create new accessors for the inherited slots (this is a CLISP extension).

## 8.2. The structure Meta-Object Protocol

The following functions accept a structure `name` as the only argument. If `DEFSTRUCT` was given the `:TYPE` option (i.e., `DEFSTRUCT` did not define a new type), then `(`FIND-CLASS` `name`)` fails (and the regular CLOS Meta-Object Protocol is not applicable), but these functions still work.

`EXT:STRUCTURE-SLOTS`
  Return the `LIST` of effective slot definition metaobjects.
`EXT:STRUCTURE-DIRECT-SLOTS`
  Return the `LIST` of direct slot definition metaobjects.
`EXT:STRUCTURE-KEYWORD-CONSTRUCTOR`
  Return the name (a `SYMBOL`) of the keyword constructor function for the structure, or `NIL` if the structure has no keyword constructor.
`EXT:STRUCTURE-BOA-CONSTRUCTORS`
  Return the `LIST` of names (`SYMBOL`s) of BOA constructors for the structure.
`EXT:STRUCTURE-COPIER`
  Return the name (a `SYMBOL`) of the copier for the structure.
`EXT:STRUCTURE-PREDICATE`
  Return the name (a `SYMBOL`) of the predicate for the structure.

## Chapter 9. Conditions [chap-9]

When an error occurred, you are in a break loop. You can evaluate forms as usual. The help command (or help key if there is one) lists the available debugger commands.

## 9.1. Embedded Newlines in Condition Reports [sec_9-1-3-1-3]

The error message prefix for the first line is “*** - ”. All subsequent lines are indented by 6 characters. Long lines are broken on whitespace (see Section 30.8, “Class `EXT:FILL-STREAM`”).

## 9.2. Mentioning Containing Function in Condition Reports [sec_9-1-3-1-5]

Contrary to the recommendation of the standard, CLISP usually does print the name of the containing function to simplify debugging in batch mode, see `EXT:EXIT-ON-ERROR`.

## 9.3. Interfaces to Restarts [sec_9-1-4-2-2]

Macro `RESTART-CASE`. In `(`RESTART-CASE` `form` {`restart-clause`}*)`, the argument list can also be specified after the keyword/value pairs instead of before them, i.e., each `restart-clause` can be either `(`restart-name` `EXT:*ARGS*` {`keyword-value-pair`}* {`form`}*)` or `(`restart-name` {`keyword-value-pair`}* `EXT:*ARGS*` {`form`}*)`.

Macro `EXT:WITH-RESTARTS`. The macro `EXT:WITH-RESTARTS` is like `RESTART-CASE`, except that the forms are specified after the restart clauses instead of before them, and the restarts created are not implicitly associated with any `CONDITION`. `(`EXT:WITH-RESTARTS` ({`restart-clause`}*) {`form`}*)` is therefore equivalent to `(`RESTART-CASE` (`PROGN` {`form`}*) {`restart-clause`}*)`.

Function `COMPUTE-RESTARTS`. `COMPUTE-RESTARTS` and `FIND-RESTART` behave as specified in [ANSI CL standard]: If the optional `condition` argument is non-`NIL`, only `RESTART`s associated with that `CONDITION` and `RESTART`s associated with no `CONDITION` at all are considered. Therefore the effect of associating a restart to a condition is not to activate it, but to hide it from other conditions. This makes the syntax-dependent implicit association performed by `RESTART-CASE` nearly obsolete.

Macro `EXT:MUFFLE-CERRORS`. The macro `(`EXT:MUFFLE-CERRORS` {`form`}*)` executes the `form`s; when a continuable `ERROR` occurs whose `CONTINUE` `RESTART` can be invoked non-interactively (this includes all continuable `ERROR`s signaled by the function `CERROR`), no message is printed, instead, the `CONTINUE` `RESTART` is invoked.

Macro `EXT:APPEASE-CERRORS`. The macro `(`EXT:APPEASE-CERRORS` {`form`}*)` executes the `form`s; when a continuable `ERROR` occurs whose `CONTINUE` `RESTART` can be invoked non-interactively (this includes all continuable `ERROR`s `SIGNAL`ed by the function `CERROR`), it is reported as a `WARNING`, and the `CONTINUE` `RESTART` is invoked.

Macro `EXT:ABORT-ON-ERROR`. The macro `(`EXT:ABORT-ON-ERROR` {`form`}*)` executes the `form`s; when an `ERROR` occurs, or when a Control+C interrupt occurs, the error message is printed and the `ABORT` `RESTART` is invoked.

Macro `EXT:EXIT-ON-ERROR`. The macro `(`EXT:EXIT-ON-ERROR` {`form`}*)` executes the `form`s; when an `ERROR` occurs, or when a Control+C interrupt occurs, the error message is printed and CLISP terminates with an error status.

Variable `CUSTOM:*REPORT-ERROR-PRINT-BACKTRACE*`. When this variable is non-`NIL` the error message printed by `EXT:ABORT-ON-ERROR` and `EXT:EXIT-ON-ERROR` includes the backtrace (stack).

Function `EXT:SET-GLOBAL-HANDLER`. The function `(`EXT:SET-GLOBAL-HANDLER` `condition` handler)` establishes a global handler for the `condition`. The `handler` should be `FUNCALL`able (a `SYMBOL` or a `FUNCTION`). If it returns, the next applicable handler is invoked, so if you do not want to land in the debugger, it should not return. E.g., the option `-on-error` `abort` and the macro `EXT:ABORT-ON-ERROR` are implemented by installing the following handler:

    (defun sys::abortonerror (condition)
      (sys::report-error condition)
      (INVOKE-RESTART (FIND-RESTART 'ABORT condition)))

When `handler` is `NIL`, the handler for `condition` is removed and returned. When `condition` is also `NIL`, all global handlers are removed and returned as a `LIST`, which can then be passed to `EXT:SET-GLOBAL-HANDLER` as the first argument and the handlers re-established.

Macro `EXT:WITHOUT-GLOBAL-HANDLERS`. The macro `(`EXT:WITHOUT-GLOBAL-HANDLERS` `&BODY` `body`)` removes all global handlers by `(`EXT:SET-GLOBAL-HANDLER` `NIL` `NIL`)`, executes `body` (where unhandled conditions now invoke the debugger), and then restores the handlers.

## 9.4. Assertions [sec_9-1-5]

The prompt for replacement values (`RESTART`s `STORE-VALUE`, `USE-VALUE` et al) is terminated with `CUSTOM:*PROMPT-FINISH*` to indicate that the value entered is treated as usual for the Lisp read-eval-print loop, i.e., it is `EVAL`uated.

## Chapter 10. Symbols [chap-10]

No notes.

## Chapter 11. Packages [chap-11]

The [ANSI CL standard] packages present in CLISP

“COMMON-LISP”
  with the nicknames “CL” and “LISP”
“COMMON-LISP-USER”
  with the nicknames “CL-USER” and “USER”
“KEYWORD”
  with no nicknames

## 11.1. Introduction to Packages [sec_11-1-1]

### 11.1.1. Function `MAKE-PACKAGE`

The default value of the `:USE` argument is `(“COMMON-LISP”)`.

`MAKE-PACKAGE` accepts additional keyword arguments `:CASE-SENSITIVE` and `:CASE-INVERTED` (but not `:MODERN`!)

### 11.1.2. Macro `DEFPACKAGE`

`DEFPACKAGE` accepts additional options `:CASE-SENSITIVE`, `:CASE-INVERTED`, and `:MODERN`.

When the package being defined already exists, it is modified as follows (and in this order):

`:CASE-SENSITIVE`
  adjusted with `(`SETF` `EXT:PACKAGE-CASE-SENSITIVE-P`)` (with a warning)
`:CASE-INVERTED`
  adjusted with `(`SETF` `EXT:PACKAGE-CASE-INVERTED-P`)` (with a warning)
`:MODERN`

  if “COMMON-LISP” is being used, it is un-used and “CS-COMMON-LISP” is used instead; also, “CS-COMMON-LISP” is used instead of “COMMON-LISP” throughout the `DEFPACKAGE` form, e.g.,

      (DEFPACKAGE "FOO"
        (:MODERN T)
        (:USE "COMMON-LISP" "EXT"))

  is equivalent to

      (DEFPACKAGE "FOO"
        (:CASE-SENSITIVE T)
        (:CASE-INVERTED T)
        (:USE "CS-COMMON-LISP" "EXT"))

  `(`:MODERN` `NIL`)` reverts the effects of `(`:MODERN` `T`)`.

`:NICKNAMES`
  adjusted with `RENAME-PACKAGE`
`:DOCUMENTATION`
  reset to the new value with `(`SETF` `DOCUMENTATION`)`
`:SHADOW`
  adjusted with `SHADOW`
`:SHADOWING-IMPORT-FROM`
  adjusted with `SHADOWING-IMPORT`
`:USE`
  adjusted with `USE-PACKAGE` and `UNUSE-PACKAGE`
`:IMPORT-FROM`
  adjusted with `IMPORT`
`:INTERN`
  adjusted with `INTERN` (but not `UNINTERN`)
`:EXPORT`
  adjusted with `INTERN` and `EXPORT` (but not `UNEXPORT`)
`:SIZE`
  ignored

### 11.1.3. Function `EXT:RE-EXPORT`

The function `(`EXT:RE-EXPORT` `FROM-PACK` `TO-PACK`)` re-`EXPORT`s all external `SYMBOL`s from `FROM-PACK` also from `TO-PACK`, provided it already uses `FROM-PACK`; and `SIGNAL`s an `ERROR` otherwise.

### 11.1.4. Function `EXT:PACKAGE-CASE-INVERTED-P`

Returns `T` if the argument is a case-inverted package. This function is `SETF`able, although it is probably not a good idea to change the case-inverted status of an existing package.

### 11.1.5. Function `EXT:PACKAGE-CASE-SENSITIVE-P`

Returns `T` if the argument is a `:CASE-SENSITIVE` `PACKAGE`. This function is `SETF`able, although it is probably not a good idea to change the case-sensitive status of an existing package.

## 11.2. Constraints on the “COMMON-LISP” Package for Conforming Programs - package locking [sec_11-1-2-1-2]

### Note

Locking discussed in this section has nothing to do with `MT:MUTEX-LOCK`.

Function `EXT:PACKAGE-LOCK` . Packages can be “locked”. When a package is locked, attempts to change its symbol table or redefine its symbols (as `DEFUN`, `DEFMACRO`, `DEFGENERIC`, `DEFVAR`, `DEFPARAMETER`, `DEFCONSTANT`, `DEFTYPE`, `DECLARATION`) result in a continuable `ERROR` (continuing overrides locking for this operation). When `CUSTOM:*SUPPRESS-CHECK-REDEFINITION*` is `T` (not a good idea!), the `ERROR` is not `SIGNAL`ed for redefine operations. Function `(`EXT:PACKAGE-LOCK` `package`)` returns the generalized boolean indicating whether the `package` is locked. A package (or a list thereof) can be locked using `(`SETF` (`EXT:PACKAGE-LOCK` `package-or-list`) `T`)`. CLISP locks its system packages (specified in the variable `CUSTOM:*SYSTEM-PACKAGE-LIST*`).

Macro `EXT:WITHOUT-PACKAGE-LOCK`. If you want to evaluate some forms with certain packages unlocked, you can use `EXT:WITHOUT-PACKAGE-LOCK` :

    (EXT:WITHOUT-PACKAGE-LOCK (“COMMON-LISP” “EXT” “CLOS”)
      (defun restart () ...))

or

    (EXT:WITHOUT-PACKAGE-LOCK (“COMMON-LISP”) (trace read-line))

`(`EXT:WITHOUT-PACKAGE-LOCK` () ...)` temporarily unlocks all packages in `CUSTOM:*SYSTEM-PACKAGE-LIST*`.

Variable `CUSTOM:*SYSTEM-PACKAGE-LIST*`. This variable specifies the default packages to be locked by `EXT:SAVEINITMEM` and unlocked by `EXT:WITHOUT-PACKAGE-LOCK` as a list of package names. You may add names to this list, e.g., a module will add its package, but you should not remove CLISP internal packages from this list.

Discussion - see also the USENET posting by Steven M. Haflich. This should prevent you from accidentally hosing yourself with

    (DEFSTRUCT instance ...)

and allow enforcing modularity. Note that you will also get the continuable `ERROR` when you try to assign (with `SETQ`, `PSETQ`, etc.) a value to an internal special variable living in a locked package and not accessible in your current `*PACKAGE*`, but only in the interpreted code and during compilation. There is no check for package locks in compiled code because of the performance considerations.

## 11.3. The “COMMON-LISP-USER” Package [sec_11-1-2-2]

The “COMMON-LISP-USER” package uses the “COMMON-LISP” and “EXT” packages.

## 11.4. Implementation-Defined Packages [sec_11-1-2-4]

The following additional packages exist:

Implementation-Defined Packages

“CLOS”
  `EXPORT`s all CLOS-specific symbols, including some additional symbols.
“SYSTEM”
  has the nickname “SYS”, and has no `EXPORT`ed symbols. It defines many system internals.
“EXT”
  is the umbrella package for all extensions: it imports and `EXT:RE-EXPORT`s all the external symbols in all CLISP extensions, so a simple `(`USE-PACKAGE` "EXT")` is enough to make all the extensions available in the current package. This package uses packages (in addition to “COMMON-LISP”): “POSIX”, “SOCKET”, “GSTREAM”, “GRAY”, “I18N”, “CUSTOM”.
“CHARSET”
  defines and `EXPORT`s some character sets, for use with `EXT:MAKE-ENCODING` and as `:EXTERNAL-FORMAT` argument.
“FFI”
  implements the foreign function interface. Some platforms only.
“SCREEN”
  defines an API for random screen access. Some platforms only.
“CS-COMMON-LISP”
“CS-COMMON-LISP-USER”
  `:CASE-SENSITIVE` versions of “COMMON-LISP” and “COMMON-LISP-USER”. See Section 11.5, “Package Case-Sensitivity”.

All pre-existing packages except “COMMON-LISP-USER” belong to the implementation, in the sense that the programs that do not follow [sec_11-1-2-1-2] (“Constraints on the ‘COMMON-LISP’ Package for Conforming Programs”) cause undefined behavior.

## 11.5. Package Case-Sensitivity

CLISP supports programs written with case sensitive symbols. For example, with case sensitive symbols, the symbols `cdr` (the function equivalent to `REST`) and the symbol `CDR` (a user-defined type denoting a Call Data Record) are different and unrelated.

There are some incompatibilities between programs assuming case sensitive symbols and programs assuming the [ANSI CL standard] case insensitive symbols. For example, `(eq 'KB 'Kb)` evaluates to false in a case sensitive world and to true in a case insensitive world. However, unlike some commercial Common Lisp implementations, CLISP allows both kinds of programs to coexist in the same process and interoperate with each other. Example:

`OLD.lisp`

      (IN-PACKAGE "OLD")
      (DEFUN FOO () ...)

`modern.lisp`

      (in-package "NEW")
      (defun bar () (old:foo))
      (symbol-name 'bar) ; ⇒ "bar"

This is achieved through specification of the symbol case policy at the package level. A modern package is one that is declared to be both case-sensitive and case-inverted and which use the symbols from the “CS-COMMON-LISP” package.

A case-sensitive package is one whose `DEFPACKAGE` declaration (or `MAKE-PACKAGE` creation form) has the option `(`:CASE-SENSITIVE` `T`)`. In a case-sensitive package, the reader does not uppercase the symbol name before calling `INTERN`. Similarly, the printer, when printing the `SYMBOL-NAME` part of a `SYMBOL` (i.e. the part after the package markers), behaves as if the readtable's case were set to `:PRESERVE`. See also Section 11.1.5, “Function `EXT:PACKAGE-CASE-SENSITIVE-P`”.

A case-inverted package is one whose `DEFPACKAGE` declaration (or `MAKE-PACKAGE` creation form) has the option `(`:CASE-INVERTED` `T`)`. In the context of a case-inverted package, symbol names are case-inverted: upper case characters are mapped to lower case, lower case characters are mapped to upper case, and other characters are left untouched. Every symbol thus conceptually has two symbol names: an old-world symbol name and a modern-world symbol name, which is the case-inverted old-world name. The first symbol name is returned by the function `SYMBOL-NAME`, the modern one by the function `cs-cl:symbol-name`. The internal functions for creating or looking up symbols in a package, which traditionally took a string argument, now conceptually take two string arguments: old-style-string and inverted-string. Actually, a function like `INTERN` takes the old-style-string as argument and computes the inverted-string from it; whereas the function `cs-cl:intern` takes the inverted-string as argument and computes the old-style-string from it. See also Section 11.1.4, “Function `EXT:PACKAGE-CASE-INVERTED-P`”.

For a few built-in functions, a variant for the case-inverted world is defined in the “CS-COMMON-LISP” package, which has the nickname “CS-CL”:

`cs-cl:symbol-name`
  returns the case-inverted symbol name.
`cs-cl:intern`
`cs-cl:find-symbol`
  work consistently with `cs-cl:symbol-name`.
`cs-cl:shadow`
`cs-cl:find-all-symbols`
`cs-cl:string=`
`cs-cl:string/=`
`cs-cl:string<`
`cs-cl:string>`
`cs-cl:string<=`
`cs-cl:string>=`
`cs-cl:string-trim`
`cs-cl:string-left-trim`
`cs-cl:string-right-trim`
  convert a `SYMBOL` to a `STRING` and therefore exist in a variant that uses `cs-cl:symbol-name` instead of `SYMBOL-NAME`.
`cs-cl:make-package`
  creates a case-inverted `PACKAGE`.

### 11.5.1. User Package for the Case-sensitive World

A package “CS-COMMON-LISP-USER” is provided for the user to modify and work in. It plays the same role as “COMMON-LISP-USER”, but for the case-sensitive world.

### 11.5.2. Package Names

The handling of package names is unchanged. Package names are still usually uppercase. The package names are also subject to `(`READTABLE-CASE` `*READTABLE*`)`.

### 11.5.3. Gensyms and Keywords

Note that gensyms and keywords are still treated traditionally: even in a case-sensitive package,

    (STRING= '#:FooBar '#:foobar)
    ⇒ T
    (EQ ':KeyWord ':keyword)
    ⇒ T

We believe this has a limited negative impact for the moment, but can be changed some time in the future.

### 11.5.4. Migration Tips

The following practices will pose no problems when migrating to a modern case-sensitive world:

- Using [ANSI CL standard] symbols in lowercase.
- Macros that create symbols by suffixing or prefixing given symbols.
- Comparing symbol names as in `(`STRING=` (`SYMBOL-NAME` `x`) (`SYMBOL-NAME` `y`))`.

The following practices will not work in a case-sensitive world or can give problems:

- Accessing the same symbol in both upper- and lowercase from the same source file.
- Macros that create symbols in other packages than the original symbols.
- Comparing `SYMBOL-NAME` return values with `EQ`.
- Comparing `(`SYMBOL-NAME` x)` with `(cs-cl:symbol-name y)`.

### 11.5.5. Using case-sensitive packages by default

CLISP supports a command-line option `-modern` that sets the `*PACKAGE*` initially to the “CS-COMMON-LISP-USER” package, and `*PRINT-CASE*` to `:DOWNCASE`.

For packages to be located in the “modern” (case-sensitive) world, you need to augment their `DEFPACKAGE` declaration by adding the option `(`:MODERN` `T`)`, see Section 11.1.2, “Macro `DEFPACKAGE`”.

## Chapter 12. Numbers [chap-12]

## 12.1. Numeric Types

The type `NUMBER` is the disjoint union of the types `REAL` and `COMPLEX` (exhaustive partition)

The type `REAL` is the disjoint union of the types `RATIONAL` and `FLOAT`.

The type `RATIONAL` is the disjoint union of the types `INTEGER` and `RATIO`.

The type `INTEGER` is the disjoint union of the types `FIXNUM` and `BIGNUM`.

The type `FLOAT` is the disjoint union of the types `SHORT-FLOAT`, `SINGLE-FLOAT`, `DOUBLE-FLOAT` and `LONG-FLOAT`.

## 12.2. Number Concepts [sec_12-1]

### 12.2.1. Numeric Operations [sec_12-1-1]

#### 12.2.1.1. Additional Integer Functions

Function `EXT:!` `(`EXT:!` `n`)` returns the factorial of `n`, `n` being a nonnegative `INTEGER`.

Function `EXT:EXQUO`. `(`EXT:EXQUO` `x` `y`)` returns the integer quotient `x/y` of two integers `x`,`y`, and `SIGNAL`s an `ERROR` when the quotient is not integer. (This is more efficient than `/`.)

Function `EXT:XGCD`. `(`EXT:XGCD` `x1` ... `xn`)` returns the values `l`, `k1`, ..., `kn`, where `l` is the greatest common divisor of the integers `x1`, ..., `xn`, and `k1`, ..., `kn` are the integer coefficients such that

    l = (GCD x1 ... xn)
      = (+ (* k1 x1) ... (* kn xn))

Function `EXT:MOD-EXPT`. `(`EXT:MOD-EXPT` `k` `l` `m`)` is equivalent to `(`MOD` (`EXPT` `k` `l`) `m`)` except it is more efficient for very large arguments.

#### 12.2.1.2. Function `DECODE-FLOAT`

`FLOAT-RADIX` always returns 2.

`(`FLOAT-DIGITS` `number` `digits`)` coerces `number` (a `REAL`) to a floating point number with at least `digits` mantissa digits. The following always evaluates to `T`:

    (>= (FLOAT-DIGITS (FLOAT-DIGITS number digits)) digits)

#### 12.2.1.3. Boolean Operations [convar_boole-_cm_boole-xor]

Table 12.1. Boolean operations

constant | value
--- | ---
`BOOLE-CLR` | 0
`BOOLE-SET` | 15
`BOOLE-1` | 10
`BOOLE-2` | 12
`BOOLE-C1` | 5
`BOOLE-C2` | 3
`BOOLE-AND` | 8
`BOOLE-IOR` | 14
`BOOLE-XOR` | 6
`BOOLE-EQV` | 9
`BOOLE-NAND` | 7
`BOOLE-NOR` | 1
`BOOLE-ANDC1` | 4
`BOOLE-ANDC2` | 2
`BOOLE-ORC1` | 13
`BOOLE-ORC2` | 11

#### 12.2.1.4. Byte Operations on Integers [sec_12-1-1-3-2]

Byte specifiers are objects of built-in type BYTE, not `INTEGER`s.

#### 12.2.1.5. Floating Point Arithmetics

Function `EXPT`. `(`EXPT` `base` `exponent`)` is not very precise if `exponent` has a large absolute value.

Function `LOG`. `(`LOG` `number` `base`)` `SIGNAL`s an `ERROR` if ``base` = 1`.

Constant `PI`. The value of `PI` is a `LONG-FLOAT` with the precision given by `(`EXT:LONG-FLOAT-DIGITS`)`. When this precision is changed, the value of `PI` is automatically recomputed. Therefore `PI` is not a constant variable.

Function `UPGRADED-COMPLEX-PART-TYPE`. When the argument is not a recognizable subtype or `REAL`, `UPGRADED-COMPLEX-PART-TYPE` `SIGNAL`s an `ERROR`, otherwise it returns its argument (even though a `COMPLEX` number in CLISP can always have `REALPART` and `IMAGPART` of any type) because it allows the most precise type inference.

Variable `CUSTOM:*DEFAULT-FLOAT-FORMAT*`. When rational numbers are to be converted to floats (due to `FLOAT`, `COERCE`, `SQRT` or a transcendental function), the result type is given by the variable `CUSTOM:*DEFAULT-FLOAT-FORMAT*`. See also `*READ-DEFAULT-FLOAT-FORMAT*`.

Macro `EXT:WITHOUT-FLOATING-POINT-UNDERFLOW`. The macro `(`EXT:WITHOUT-FLOATING-POINT-UNDERFLOW` {`form`}*)` executes the `form`s, with errors of type `FLOATING-POINT-UNDERFLOW` inhibited. Floating point operations will silently return zero instead of `SIGNAL`ing an `ERROR` of type `FLOATING-POINT-UNDERFLOW`.

Condition `FLOATING-POINT-INVALID-OPERATION`. This `CONDITION` is never `SIGNAL`ed by CLISP.

Condition `FLOATING-POINT-INEXACT`. This `CONDITION` is never `SIGNAL`ed by CLISP.

### 12.2.2. Implementation-Dependent Numeric Constants [sec_12-1-2]

#### 12.2.2.1. Fixnum Limits

Table 12.2. Fixnum limits

CPU type | 32-bit CPU | 64-bit CPU
--- | --- | ---
`MOST-POSITIVE-FIXNUM` | 224-1 = 16777215 | 248-1 = 281474976710655
`MOST-NEGATIVE-FIXNUM` | -224 = -16777216 | -248 = -281474976710656

#### 12.2.2.2. Bignum Limits

`BIGNUM`s are limited in size. Their maximum size is `32*(216-2)=2097088` bits. The largest representable `BIGNUM` is therefore `22097088-1`.

#### 12.2.2.3. Float Limits

Together with `PI`, the other `LONG-FLOAT` constants

`LEAST-NEGATIVE-LONG-FLOAT` | `LONG-FLOAT-EPSILON`
`LEAST-NEGATIVE-NORMALIZED-LONG-FLOAT` | `LONG-FLOAT-NEGATIVE-EPSILON`
`LEAST-POSITIVE-LONG-FLOAT` | `MOST-NEGATIVE-LONG-FLOAT`
`LEAST-POSITIVE-NORMALIZED-LONG-FLOAT` | `MOST-POSITIVE-LONG-FLOAT`

are recomputed whenever `(`EXT:LONG-FLOAT-DIGITS`)` is `SETF`ed. They are not constant variables.

### Warning

Since the exponent of a `LONG-FLOAT` is a signed 32-bits integer, `MOST-POSITIVE-LONG-FLOAT` is about `2231`, which is much larger that the largest representable `BIGNUM`, which is less than `2221`. This, obviously, means that `ROUND`, `TRUNCATE`, `FLOOR` and `CEILING` `SIGNAL`s an `ERROR` on large `LONG-FLOAT`s. Less obviously, this means that `(`FORMAT` `NIL` "`~E`" `MOST-POSITIVE-LONG-FLOAT`)` also fails.

### 12.2.3. Rule of Float Substitutability [sec_12-1-3-3]

When a mathematical function may return an exact (`RATIONAL`) or inexact (`FLOAT`) result, it always returns the exact result.

### 12.2.4. Floating-point Computations [sec_12-1-4]

There are four floating point types: `SHORT-FLOAT`, `SINGLE-FLOAT`, `DOUBLE-FLOAT` and `LONG-FLOAT`:

type | sign | mantissa | exponent | comment
--- | --- | --- | --- | ---
`SHORT-FLOAT` | 1 bit | 16+1 bits | 8 bits | immediate
`SINGLE-FLOAT` | 1 bit | 23+1 bits | 8 bits | IEEE 754
`DOUBLE-FLOAT` | 1 bit | 52+1 bits | 11 bits | IEEE 754
`LONG-FLOAT` | 1 bit | >=64 bits | 32 bits | variable length

The single and double float formats are those of the IEEE 754 “Standard for Binary Floating-Point Arithmetic”, except that CLISP does not support features like `±0`, `±inf`, `NaN`, gradual underflow, etc. Common Lisp does not make use of these features, so, to reduce portability problems, CLISP by design returns the same floating point results on all platforms (CLISP has a floating-point emulation built in for platforms that do not support IEEE 754). Note that

- When you got a `NaN` in your program, your program is broken, so you will spend time determining where the `NaN` came from. It is better to `SIGNAL` an `ERROR` in this case.
- When you got unnormalized floats in your program, your results will have a greatly reduced accuracy anyway. Since CLISP has the means to cope with this - `LONG-FLOAT`s of variable precision - it does not need unnormalized floats.

This is why `*FEATURES*` does not contain the `:IEEE-FLOATING-POINT` keyword.

Arbitrary Precision Floats. `LONG-FLOAT`s have variable mantissa length, which is a multiple of 16 (or 32, depending on the word size of the processor). The default length used when `LONG-FLOAT`s are `READ` is given by the place `(`EXT:LONG-FLOAT-DIGITS`)`. It can be set by `(`SETF` (`EXT:LONG-FLOAT-DIGITS`) `n`)`, where `n` is a positive `INTEGER`. E.g., `(`SETF` (`EXT:LONG-FLOAT-DIGITS`) 3322)` sets the default precision of `LONG-FLOAT`s to about 1000 decimal digits.

#### 12.2.4.1. Rule of Float Precision Contagion [sec_12-1-4-4]

The floating point contagion is controlled by the variable `CUSTOM:*FLOATING-POINT-CONTAGION-ANSI*`. When it is non-`NIL`, contagion is done as per the [ANSI CL standard]: `SHORT-FLOAT` → `SINGLE-FLOAT` → `DOUBLE-FLOAT` → `LONG-FLOAT`.

Rationale:
  See it pragmatically: save what you can and let others worry about the rest.
Brief:
  Common Lisp knows the number's precision, not accuracy, so preserving the precision can be accomplished reliably, while anything relating to the accuracy is just a speculation - only the user (programmer) knows what it is in each case.
Detailed:
  A computer float is an approximation of a real number. One can think of it as a random variable with the mean equal to itself and standard deviation equal to half the last significant digit. E.g., `1.5` is actually `1.5±0.05`. Consider adding `1.5` and `1.75`. [ANSI CL standard] requires that `(`+` 1.5 1.75)` return 3.25, while traditional CLISP would return 3.3. The implied random variables are: `3.25±0.005` and `3.3±0.05`. Note that the traditional CLISP way does lie about the mean: the mean is `3.25` and nothing else, while the standard way could be lying about the deviation (accuracy): if the implied accuracy of `1.5` (i.e., 0.05) is its actual accuracy, then the accuracy of the result cannot be smaller that that. Therefore, since Common Lisp has no way of knowing the actual accuracy, [ANSI CL standard] (and all the other standard engineering programming languages, like C, Fortran etc) decided that keeping the accuracy correct is the business of the programmer, while the language should preserve what it can - the precision.
Experience:
  Rounding errors accumulate, and if a computation is conducted with insufficient precision, an outright incorrect result can be returned. (E.g., `E(x2) - E(x)2` can be negative!) The user should not mix floats of different precision (that's what `CUSTOM:*WARN-ON-FLOATING-POINT-CONTAGION*` is for), but one should not be penalized for this too harshly.

When `CUSTOM:*FLOATING-POINT-CONTAGION-ANSI*` is `NIL`, the traditional CLISP method is used, namely the result of an arithmetic operation whose arguments are of different float types is rounded to the float format of the shortest (least precise) of the arguments: `RATIONAL` → `LONG-FLOAT` → `DOUBLE-FLOAT` → `SINGLE-FLOAT` → `SHORT-FLOAT` (in contrast to [sec_12-1-4-4]!)

Rationale:
  See it mathematically. Add intervals: `{1.0 ± 1e-8} + {1.0 ± 1e-16} = {2.0 ± 1e-8}`. So, if we add `1.0s0` and `1.0d0`, we should get `2.0s0`.
Brief:
  Do not suggest high accuracy of a result by giving it a precision that is greater than its accuracy.
Example:
  `(`-` (`+` 1.7 `PI`) `PI`)` should not return 1.700000726342836417234L0, it should return 1.7f0 (or 1.700001f0 if there were rounding errors).
Experience:
  If in a computation using thousands of `SHORT-FLOAT`s, a `LONG-FLOAT` (like `PI`) happens to be used, the long precision should not propagate throughout all the intermediate values. Otherwise, the long result would look precise, but its accuracy is only that of a `SHORT-FLOAT`; furthermore much computation time would be lost by calculating with `LONG-FLOAT`s when only `SHORT-FLOAT`s would be needed.

##### Variable `CUSTOM:*WARN-ON-FLOATING-POINT-CONTAGION*`

If the variable `CUSTOM:*WARN-ON-FLOATING-POINT-CONTAGION*` is non-`NIL`, a `WARNING` is emitted for every coercion involving different floating-point types. As explained above, float precision contagion is not a good idea. You can avoid the contagion by doing all your computations with the same floating-point type (and using `FLOAT` to convert all constants, e.g., `PI`, to your preferred type).

This variable helps you eliminate all occurrences of float precision contagion: set it to `T` to have CLISP `SIGNAL` a `WARNING` on float precision contagion; set it to `ERROR` to have CLISP `SIGNAL` an `ERROR` on float precision contagion, so that you can look at the stack backtrace.

#### 12.2.4.2. Rule of Float and Rational Contagion [sec_12-1-4-1]

The contagion between floating point and rational numbers is controlled by the variable `CUSTOM:*FLOATING-POINT-RATIONAL-CONTAGION-ANSI*`. When it is non-`NIL`, contagion is done as per the [ANSI CL standard]: `RATIONAL` → `FLOAT`.

When `CUSTOM:*FLOATING-POINT-RATIONAL-CONTAGION-ANSI*` is `NIL`, the traditional CLISP method is used, namely if the result is mathematically an exact rational number, this rational number is returned (in contrast to [sec_12-1-4-1]!)

`CUSTOM:*FLOATING-POINT-RATIONAL-CONTAGION-ANSI*` has an effect only in those few cases when the mathematical result is exact although one of the arguments is a floating-point number, such as `(`*` 0 1.618)`, `(`/` 0 1.618)`, `(`ATAN` 0 1.0)`, `(`EXPT` 2.0 0)`, `(`PHASE` 2.718)`.

##### Variable `CUSTOM:*WARN-ON-FLOATING-POINT-RATIONAL-CONTAGION*`

If the variable `CUSTOM:*WARN-ON-FLOATING-POINT-RATIONAL-CONTAGION*` is non-`NIL`, a `WARNING` is emitted for every avoidable coercion from a rational number to a floating-point number. You can avoid such coercions by calling `FLOAT` to convert the particular rational numbers to your preferred floating-point type.

This variable helps you eliminate all occurrences of avoidable coercions to a floating-point number when a rational number result would be possible: set it to `T` to have CLISP `SIGNAL` a `WARNING` in such situations; set it to `ERROR` to have CLISP `SIGNAL` an `ERROR` in such situations, so that you can look at the stack backtrace.

##### Variable `CUSTOM:*PHASE-ANSI*`

A similar variable, `CUSTOM:*PHASE-ANSI*`, controls the return value of `PHASE` when the argument is an exact nonnegative `REAL`. Namely, if `CUSTOM:*PHASE-ANSI*` is non-`NIL`, it returns a floating-point zero; if `CUSTOM:*PHASE-ANSI*` is `NIL`, it returns an exact zero. Example: `(`PHASE` 2/3)`

### 12.2.5. Complex Computations [sec_12-1-5]

Complex numbers can have a real part and an imaginary part of different types. For example, `(`SQRT` -9.0)` evaluates to the number ``#C`(0 3.0)`, which has a real part of exactly `0`, not only `0.0` (which would mean “approximately 0”).

The type specifier for this is `(`COMPLEX` `INTEGER` `SINGLE-FLOAT`)`, and `(`COMPLEX` `type-of-real-part` `type-of-imaginary-part`)` in general.

The type specifier `(`COMPLEX` `type`)` is equivalent to `(`COMPLEX` `type` `type`)`.

### 12.2.6. Rule of Canonical Representation for Complex Rationals [sec_12-1-5-3]

Complex numbers can have a real part and an imaginary part of different types. If the imaginary part is `EQL` to `0`, the number is automatically converted to a real number.

This has the advantage that `(`LET` ((x (`SQRT` -9.0))) (* x x))` - instead of evaluating to ``#C`(-9.0 0.0)`, with `x` = ``#C`(0.0 3.0)` - evaluates to ``#C`(-9.0 0)` = `-9.0`, with `x` = ``#C`(0 3.0)`.

### 12.2.7. Random-State Operations [sec_12-1-7]

To ease reproducibility, the variable `*RANDOM-STATE*` is initialized to the same value on each invocation, so that

    $ clisp -norc -x '(RANDOM 1s0)'

will always print the same number.

If you want a new random state on each invocation, you can arrange for that by using init function:

    $ clisp -norc -x '(EXT:SAVEINITMEM "foo" :init-function (LAMBDA () (SETQ *RANDOM-STATE* (MAKE-RANDOM-STATE T))))'
    $ clisp -norc -M foo.mem -x '(RANDOM 1s0)'

or by placing `(`SETQ` `*RANDOM-STATE*` (`MAKE-RANDOM-STATE` `T`))` into your RC file.

## Chapter 13. Characters [chap-13]

## 13.1. Introduction to Characters [sec_13-1]

### 13.1.1. Function `CHAR-CODE`

`CHAR-CODE` takes values from `0` (inclusive) to `CHAR-CODE-LIMIT` (exclusive), i.e., the implementation supports exactly `CHAR-CODE-LIMIT` characters.

Table 13.1. Number of characters

binaries built | without UNICODE support | with UNICODE support
--- | --- | ---
`CHAR-CODE-LIMIT` | 28 = 256 | 17 * 216 = 1114112

### 13.1.2. Type `BASE-CHAR`

The types `EXT:STRING-CHAR` and `BASE-CHAR` are equivalent to `CHARACTER`. `EXT:STRING-CHAR` used to be available as `STRING-CHAR` prior to removal from [ANSI CL standard] by CHARACTER-PROPOSAL:2.

### 13.1.3. Function `EXT:CHAR-WIDTH`

`(`EXT:CHAR-WIDTH` `char`)` returns the number of screen columns occupied by `char`. The value is

0
  for non-spacing characters (such as control characters and many combining characters);
2
  for double-width East Asian characters;
1
  for all other characters.

See also function `EXT:STRING-WIDTH`.

## 13.2. Character sets

The characters are ordered according to a superset of the ASCII character set.

Platform Dependent: Only in CLISP built with compile-time flag UNICODE
  More precisely, CLISP uses the 21-bit Unicode 3.2 character set (ISO 10646, also known as UCS-4).

Platform Dependent: Only in CLISP built without compile-time flag UNICODE

  More precisely, CLISP uses the ISO Latin-1 (ISO 8859-1) character set:

  | #x0 | #x1 | #x2 | #x3 | #x4 | #x5 | #x6 | #x7 | #x8 | #x9 | #xA | #xB | #xC | #xD | #xE | #xF
  --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
  #x00 | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | **
  #x10 | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | ** | **
  #x20 |  | ! | " | # | $ | % | & | ' | ( | ) | * | + | , | - | . | /
  #x30 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | : | ; | < | = | > | ?
  #x40 | @ | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O
  #x50 | P | Q | R | S | T | U | V | W | X | Y | Z | [ | \ | ] | ^ | _
  #x60 | ` | a | b | c | d | e | f | g | h | i | j | k | l | m | n | o
  #x70 | p | q | r | s | t | u | v | w | x | y | z | { | | | } | ~ |
  #x80 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
  #x90 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
  #xA0 |  | ¡ | ¢ | £ | ¤ | ¥ | ¦ | § | ¨ | © | ª | « | ¬ |  | ® | ¯
  #xB0 | ° | ± | ² | ³ | ´ | µ | ¶ | · | ¸ | ¹ | º | » | ¼ | ½ | ¾ | ¿
  #xC0 | À | Á | Â | Ã | Ä | Å | Æ | Ç | È | É | Ê | Ë | Ì | Í | Î | Ï
  #xD0 | Ð | Ñ | Ò | Ó | Ô | Õ | Ö | × | Ø | Ù | Ú | Û | Ü | Ý | Þ | ß
  #xE0 | à | á | â | ã | ä | å | æ | ç | è | é | ê | ë | ì | í | î | ï
  #xF0 | ð | ñ | ò | ó | ô | õ | ö | ÷ | ø | ù | ú | û | ü | ý | þ | ÿ

  Here ** are control characters, not graphic characters. (The characters left blank here cannot be represented in this character set).

Table 13.2. Standard characters

character | code
--- | ---
#\Space | #x20
#\Newline | #x0A

Table 13.3. Semi-standard characters

character | code
--- | ---
#\Backspace | #x08
#\Tab | #x09
#\Linefeed | #x0A
#\Page | #x0C
#\Return | #x0D

#\Newline is the line terminator.

Table 13.4. Additional Named Characters

character | code
--- | ---
#\Null | #x00
#\Bell | #x07
#\Escape | #x1B

Table 13.5. Additional syntax for characters with code from #x00 to #x1F:

character | code
--- | ---
#\^@ | #x00
#\^A … #\^Z | #x01 … #x1A
#\^[ | #x1B
#\^\ | #x1C
#\^] | #x1D
#\^^ | #x1E
#\^_ | #x1F

See also Section 2.6.1, “Sharpsign Backslash sec_2-4-8-1”.

## 13.3. Character Scripts [sec_13-1-2-1]

The only defined character script is the type `CHARACTER` itself.

## 13.4. Character Attributes [sec_13-1-3]

Characters have no implementation-defined or [CLtL1] font and bit attributes. All characters are simple characters.

### 13.4.1. Input Characters

For backward compatibility, there is a class `SYS::INPUT-CHARACTER` representing either a character with font and bits, or a keystroke. The following functions work with objects of types `CHARACTER` and `SYS::INPUT-CHARACTER`. Note that `EQL` or `EQUAL` are equivalent to `EQ` on objects of type `SYS::INPUT-CHARACTER`.

`EXT:CHAR-FONT-LIMIT` = 16
  The system uses only font 0.
`EXT:CHAR-BITS-LIMIT` = 16

  Character bits:

  key | value
  --- | ---
  `:CONTROL` | `EXT:CHAR-CONTROL-BIT`
  `:META` | `EXT:CHAR-META-BIT`
  `:SUPER` | `EXT:CHAR-SUPER-BIT`
  `:HYPER` | `EXT:CHAR-HYPER-BIT`

`(`EXT:CHAR-FONT` `object`)`
  returns the font of a `CHARACTER` or `SYS::INPUT-CHARACTER`.
`(`EXT:CHAR-BITS` `object`)`
  returns the bits of a `CHARACTER` or `SYS::INPUT-CHARACTER`.
`(`EXT:MAKE-CHAR` `char` [`bits` [`font`]])`
  returns a new `SYS::INPUT-CHARACTER`, or `NIL` if such a character cannot be created.
`(`EXT:CHAR-BIT` `object` `name`)`
  returns `T` if the named bit is set in `object`, else `NIL`.
`(`EXT:SET-CHAR-BIT` `object` `name` `new-value`)`
  returns a new `SYS::INPUT-CHARACTER` with the named bit set or unset, depending on the `BOOLEAN` `new-value`.

### Warning

`SYS::INPUT-CHARACTER` is not a subtype of `CHARACTER`.

Platform Dependent: UNIX, Win32 platforms only.
  The system itself uses this `SYS::INPUT-CHARACTER` type only to mention special keys and Control/Alternate/Shift key status on return from `(`READ-CHAR` `EXT:*KEYBOARD-INPUT*`)`.

## 13.5. Graphic Characters [sec_13-1-4-1]

The graphic characters are those UNICODE characters which are defined by the UNICODE standard, excluding the ranges U0000 … U001F and U007F … U009F.

## 13.6. Alphabetic Characters [sec_13-1-4-2]

The alphabetic characters are those UNICODE characters which are defined as letters by the UNICODE standard, e.g., the ASCII characters

`ABCDEFGHIJKLMNOPQRSTUVWXYZ
abcdefghijklmnopqrstuvwxyz`

and the international alphabetic characters from the character set:

`ÇüéâäàåçêëèïîìÄÅÉæÆôöòûùÿÖÜßáíóúñÑªºãõØøÀÃÕ`

etc.

## 13.7. Characters With Case [sec_13-1-4-3]

### 13.7.1. Function `EXT:CHAR-INVERTCASE`

`(`EXT:CHAR-INVERTCASE` `char`)` returns the corresponding character in the other case for `CHAR`, i.e., `CHAR-UPCASE` for a lowercase character and `CHAR-DOWNCASE` for an uppercase character; for a character that does not have a case attribute, the argument is returned. See also `EXT:STRING-INVERTCASE` and `EXT:NSTRING-INVERTCASE`.

### 13.7.2. Case of Implementation-Defined Characters [sec_13-1-4-3-4]

The characters with case are those UNICODE characters `c`, for which the upper case mapping `uc` and the lower case mapping `lc` have the following properties:

- `uc` and `lc` are different
- `c` is one of `uc` and `lc`
- the upper case mapping of `uc` and of `lc` is `uc`
- the lower case mapping of `uc` and of `lc` is `lc`

The titlecase property of UNICODE characters has no equivalent in Common Lisp.

## 13.8. Numeric Characters [sec_13-1-4-4]

The numeric characters are those UNICODE characters which are defined as digits by the UNICODE standard.

## 13.9. Ordering of Characters [sec_13-1-6]

The characters are ordered according to their UNICODE code.

The functions `CHAR-EQUAL` `CHAR-NOT-EQUAL`, `CHAR-LESSP`, `CHAR-GREATERP`, `CHAR-NOT-GREATERP`, `CHAR-NOT-LESSP` ignore bits and font attributes of their arguments.

## 13.10. Character Names [sec_13-1-7]

Character names of non-ASCII characters are the names defined by UNICODE, with spaces replaced by underscores, and converted to upper case. There are two exceptions, though:

#\U0001F514
  has the name `UNICODE_BELL`, because the name `BELL` is already taken by the ASCII control character with code 7 (the audible bell character).
#\U0001F5CF
  has the name `UNICODE_PAGE`, because the name `PAGE` is already taken by the ASCII control character with code 12 (the form feed or page separator character).

## 13.11. Treatment of Newline during Input and Output [sec_13-1-8]

Newlines are written according to the stream's `EXT:ENCODING`, see the function `STREAM-EXTERNAL-FORMAT` and the description of `EXT:ENCODING`s, in particular, line terminators. The default behavior is as follows:

Platform Dependent: Win32 platform only.
  When writing to a file, #\Newline is converted to CR/LF. (This is the usual convention on DOS.) For example, #\Return+#\Newline is written as CR/CR/LF.

When reading from a file, CR/LF is converted to #\Newline (the usual convention on DOS), and CR not followed by LF is converted to #\Newline as well (the usual conversion on MacOS, also used by some programs on Win32). If you do not want this, i.e., if you really want to distinguish LF, CR and CR/LF, you have to resort to binary input (function `READ-BYTE`).

Justification. Unicode Newline Guidelines say: “Even if you know which characters represents NLF on your particular platform, on input and in interpretation, treat CR, LF, CRLF, and NEL the same. Only on output do you need to distinguish between them.”

Rationale. In CLISP, #\Newline is identical to #\Linefeed (which is specifically permitted by the [ANSI CL standard] in [sec_13-1-7] “Character Names”). Consider a file containing exactly this string: `(`CONCATENATE` '`STRING` "foo" (`STRING` #\Linefeed) "bar" (`STRING` #\Return) (`STRING` #\Linefeed))` Suppose we open it with `(`OPEN` "foo" `:EXTERNAL-FORMAT` `:DOS`)`. What should `READ-LINE` return? Right now, it returns "foo" (the second `READ-LINE` returns "bar" and reaches `end-of-stream`). If our i/o were “faithful”, `READ-LINE` would have returned the string `(`CONCATENATE` '`STRING` "foo" (`STRING` #\Linefeed) "bar")`, i.e., a string with an embedded #\Newline between "foo" and "bar" (because a single #\Linefeed is not a #\Newline in the specified `:EXTERNAL-FORMAT`, it will not make `READ-LINE` return, but it is a CLISP #\Newline!) Even though the specification for `READ-LINE` does not explicitly forbids newlines inside the returned string, such behavior would be quite surprising, to say the least. Moreover, this line (with an embedded #\Newline) would be written as two lines (when writing to a `STREAM` with `:EXTERNAL-FORMAT` of `:DOS`), because the embedded #\Newline would be written as CR+LF.

## 13.12. Character Encodings [sec_13-1-9]

The integer returned by `CHAR-INT` is the same as the character's code (`CHAR-CODE`).

## 13.13. Documentation of Implementation-Defined Scripts [sec_13-1-10]

See Section 31.5, “Encodings”.

## 13.14. Platform-Dependent Characters

The characters that are not graphic chars and the space character have names:

Table 13.6. Additional characters (Platform Dependent: Win32 platform only.)

code | char
--- | ---
`(`CODE-CHAR` #x00)` | #\Null
`(`CODE-CHAR` #x07)` | #\Bell
`(`CODE-CHAR` #x08)` | #\Backspace
`(`CODE-CHAR` #x09)` | #\Tab
`(`CODE-CHAR` #x0A)` | #\Newline | #\Linefeed
`(`CODE-CHAR` #x0B)` | #\Code11
`(`CODE-CHAR` #x0C)` | #\Page
`(`CODE-CHAR` #x0D)` | #\Return
`(`CODE-CHAR` #x1A)` | #\Code26
`(`CODE-CHAR` #x1B)` | #\Escape | #\Esc
`(`CODE-CHAR` #x20)` | #\Space
`(`CODE-CHAR` #x7F)` | #\Rubout

Table 13.7. Additional characters (Platform Dependent: UNIX platform only.)

code | char
--- | ---
`(`CODE-CHAR` #x00)` | #\Null | #\Nul
`(`CODE-CHAR` #x01)` | #\Soh
`(`CODE-CHAR` #x02)` | #\Stx
`(`CODE-CHAR` #x03)` | #\Etx
`(`CODE-CHAR` #x04)` | #\Eot
`(`CODE-CHAR` #x05)` | #\Enq
`(`CODE-CHAR` #x06)` | #\Ack
`(`CODE-CHAR` #x07)` | #\Bell | #\Bel
`(`CODE-CHAR` #x08)` | #\Backspace | #\Bs
`(`CODE-CHAR` #x09)` | #\Tab | #\Ht
`(`CODE-CHAR` #x0A)` | #\Newline | #\Nl | #\Linefeed
`(`CODE-CHAR` #x0B)` | #\Vt
`(`CODE-CHAR` #x0C)` | #\Page | #\Np
`(`CODE-CHAR` #x0D)` | #\Return | #\Cr
`(`CODE-CHAR` #x0E)` | #\So
`(`CODE-CHAR` #x0F)` | #\Si
`(`CODE-CHAR` #x10)` | #\Dle
`(`CODE-CHAR` #x11)` | #\Dc1
`(`CODE-CHAR` #x12)` | #\Dc2
`(`CODE-CHAR` #x13)` | #\Dc3
`(`CODE-CHAR` #x14)` | #\Dc4
`(`CODE-CHAR` #x15)` | #\Nak
`(`CODE-CHAR` #x16)` | #\Syn
`(`CODE-CHAR` #x17)` | #\Etb
`(`CODE-CHAR` #x18)` | #\Can
`(`CODE-CHAR` #x19)` | #\Em
`(`CODE-CHAR` #x1A)` | #\Sub
`(`CODE-CHAR` #x1B)` | #\Escape | #\Esc
`(`CODE-CHAR` #x1C)` | #\Fs
`(`CODE-CHAR` #x1D)` | #\Gs
`(`CODE-CHAR` #x1E)` | #\Rs
`(`CODE-CHAR` #x1F)` | #\Us
`(`CODE-CHAR` #x20)` | #\Space | #\Sp
`(`CODE-CHAR` #x7F)` | #\Rubout | #\Delete | #\Del

## 13.15. Obsolete Constants

Table 13.8. Character bit constants (obsolete)

constant | value
--- | ---
`EXT:CHAR-CONTROL-BIT` | 1
`EXT:CHAR-META-BIT` | 2
`EXT:CHAR-SUPER-BIT` | 4
`EXT:CHAR-HYPER-BIT` | 8

## Chapter 14. Conses [chap-14]

## 14.1. Conses as Lists [sec_14-1-2]

### 14.1.1. Mapping Functions

Function `EXT:MAPCAP`. The function `EXT:MAPCAP` is like `MAPCAN`, except that it concatenates the resulting lists with `APPEND` instead of `NCONC`:

    (EXT:MAPCAP function x1 ... xn) ≡
    (APPLY #'APPEND (MAPCAR function x1 ... xn))

(Actually a bit more efficient that this would have been.)

Function `EXT:MAPLAP`. The function `EXT:MAPLAP` is like `MAPCON`, except that it concatenates the resulting lists with `APPEND` instead of `NCONC`:

    (EXT:MAPLAP function x1 ... xn) ≡
    (APPLY #'APPEND (MAPLIST function x1 ... xn))

(Actually a bit more efficient that this would have been.)

## Chapter 15. Arrays [chap-15]

Function `MAKE-ARRAY`. `MAKE-ARRAY` can return specialized arrays for the `ARRAY-ELEMENT-TYPE`s `(`UNSIGNED-BYTE` 2)`, `(`UNSIGNED-BYTE` 4)`, `(`UNSIGNED-BYTE` 8)`, `(`UNSIGNED-BYTE` 16)`, `(`UNSIGNED-BYTE` 32)`, and, of course, the required specializations `NIL`, `BIT` and `CHARACTER`.

Function `ADJUST-ARRAY` for displaced arrays. An array to which another array is displaced should not be shrunk (using `ADJUST-ARRAY`) in such a way that the other array points into void space. This cannot be checked at the time `ADJUST-ARRAY` is called!

## 15.1. Array Elements [sec_15-1-1]

Table 15.1. Array limits

CPU type | 32-bit CPU | 64-bit CPU
--- | --- | ---
`ARRAY-RANK-LIMIT` | 212 = 4096
`ARRAY-DIMENSION-LIMIT` | 224-1 = 16777215 | 232-1 = 4294967295
`ARRAY-TOTAL-SIZE-LIMIT` | 224-1 = 16777215 | 232-1 = 4294967295

## Chapter 16. Strings [chap-16]

## 16.1. Miscellaneous

### 16.1.1. String Comparison

String comparison (`STRING<` and friends) is based on the function `CHAR<=` (see Section 13.9, “Ordering of Characters sec_13-1-6”). Therefore diphthongs do not obey the usual national rules. Example: `o < oe < z < ö`.

### 16.1.2. Function `EXT:STRING-WIDTH`

`(`EXT:STRING-WIDTH` `string` `&KEY` `start` `end`)` returns the number of screen columns occupied by `string`. This is computed as the sum of all `EXT:CHAR-WIDTH`s of all of the `string`'s characters:

    (REDUCE #'+ string :KEY #'EXT:CHAR-WIDTH)

### 16.1.3. Functions `EXT:STRING-INVERTCASE` and `EXT:NSTRING-INVERTCASE`

`(`EXT:STRING-INVERTCASE` `string` `&KEY` `start` `end`)` and `(`EXT:NSTRING-INVERTCASE` `string` `&KEY` `start` `end`)` are similar to `STRING-UPCASE` et al: they use `EXT:CHAR-INVERTCASE` to invert the case of each characters in the argument string region.

## Chapter 17. Sequences [chap-17]

## 17.1. Additional Functions

### 17.1.1. Function `EXT:TRIM-IF`

Function `(`EXT:TRIM-IF` `predicate` `sequence`)` returns the portion of `sequence` without the leading and trailing elements which match `predicate`.

## 17.2. Additional Macros

### 17.2.1. Macro `EXT:DOSEQ`

For iteration through a sequence, a macro `EXT:DOSEQ`, similar to `DOLIST`, may be used instead of `MAP`:

    (EXT:DOSEQ (variable sequence-form [result-form])
      {declaration}*
      {tag|form}*)

`EXT:DOSEQ` forms are iteration forms.

## 17.3. Functions `NREVERSE` & `NRECONC`

Function `NREVERSE`. The result of `NREVERSE` is always `EQ` to the argument. `NREVERSE` on a `VECTOR` swaps pairs of elements. `NREVERSE` on a `LIST` swaps the first and the last element and reverses the list chaining between them.

Function `NRECONC`. The result of `NRECONC` is `EQ` to the first argument unless it is `NIL`, in which case the result is `EQ` to the second argument.

## 17.4. Functions `REMOVE` & `DELETE`

`REMOVE`, `REMOVE-IF`, `REMOVE-IF-NOT`, `REMOVE-DUPLICATES` return their argument unchanged, if no element has to be removed.

`DELETE`, `DELETE-IF`, `DELETE-IF-NOT`, `DELETE-DUPLICATES` destructively modify their argument: If the argument is a `LIST`, the `CDR` parts are modified. If the argument is a `VECTOR` with fill pointer, the fill pointer is lowered and the remaining elements are compacted below the new fill pointer.

Variable `CUSTOM:*SEQUENCE-COUNT-ANSI*`. Contrary to the [ANSI CL standard] issue RANGE-OF-COUNT-KEYWORD:NIL-OR-INTEGER, negative `:COUNT` keyword arguments are not allowed unless you set `CUSTOM:*SEQUENCE-COUNT-ANSI*` to a non-`NIL` value, in which case “using a negative integer value is functionally equivalent to using a value of zero”, as per the [ANSI CL standard] issue.

## 17.5. Functions `SORT` & `STABLE-SORT`

`SORT` and `STABLE-SORT` accept two additional keyword arguments `:START` and `:END`:

    (SORT sequence predicate &KEY :KEY :START :END)
    (STABLE-SORT sequence predicate &KEY :KEY :START :END)

`SORT` and `STABLE-SORT` are identical. They implement the mergesort algorithm. Worst case complexity: `O(n*log(n))` comparisons, where `n` is the `LENGTH` of the subsequence bounded by the `:START` and `:END` arguments.

## Chapter 18. Hash Tables [chap-18]

## 18.1. Modifying Hash Table Keys [sec_18-1-2]

If you “visibly modify” a key, consequences are unpredictable:

    (LET ((hash-table (MAKE-HASH-TABLE :test 'EQUALP)))
      (SETF (GETHASH hash-table hash-table) T)
      (GETHASH hash-table hash-table))
    ⇒ NIL ;
    ⇒ NIL

because `(`SETF` `GETHASH`)` modifies `hash-table`, the very next `GETHASH` does not find it in itself.

## 18.2. Function `MAKE-HASH-TABLE`

`MAKE-HASH-TABLE` accepts two additional keyword arguments `:INITIAL-CONTENTS` and `:WEAK`:

    (MAKE-HASH-TABLE &KEY :TEST :INITIAL-CONTENTS :SIZE
                     :REHASH-SIZE :REHASH-THRESHOLD
                     :WARN-IF-NEEDS-REHASH-AFTER-GC :WEAK)

The `:TEST` argument can be, other than one of the symbols `EQ`, `EQL`, `EQUAL`, `EQUALP`, one of the symbols `EXT:FASTHASH-EQ` and `EXT:STABLEHASH-EQ`. Both of these tests use `EQ` as the comparison function; they differ in their performance characteristics.

`EXT:FASTHASH-EQ`
  This uses the fastest possible hash function. Its drawback is that its hash codes become invalid at every garbage-collection (except if all keys are immediate objects), thus requiring a reorganization of the hash table at the first access after each garbage-collection. Especially when generational garbage-collection is used, which leads to frequent small garbage-collections, large hash table with this test can lead to scalability problems.
`EXT:STABLEHASH-EQ`
  This uses a slower hash function that has the property that its hash codes for instances of the classes `SYMBOL`, `EXT:STANDARD-STABLEHASH` (subclass of `STANDARD-OBJECT`) and `EXT:STRUCTURE-STABLEHASH` (subclass of `STRUCTURE-OBJECT`) are stable across GCs. This test can thus avoid the scalability problems if all keys, other than immediate objects, are `SYMBOL`, `EXT:STANDARD-STABLEHASH` or `EXT:STRUCTURE-STABLEHASH` instances.

One can recommend to use `EXT:FASTHASH-EQ` for short-lived hash tables. For tables with a longer lifespan which can be big or accessed frequently, it is recommended to use `EXT:STABLEHASH-EQ`, and to modify the objects that are used as its keys to become instances of `EXT:STANDARD-STABLEHASH` or `EXT:STRUCTURE-STABLEHASH`.

When the symbol `EQ` or the function `#'eq` is used as a `:TEST` argument, the value of the variable `CUSTOM:*EQ-HASHFUNCTION*` is used instead. This value must be one of `EXT:FASTHASH-EQ`, `EXT:STABLEHASH-EQ`.

Similarly, the `:TEST` argument can also be one of the symbols `EXT:FASTHASH-EQL`, `EXT:STABLEHASH-EQL`, `EXT:FASTHASH-EQUAL`, `EXT:STABLEHASH-EQUAL`. The same remarks apply as for `EXT:FASTHASH-EQ` and `EXT:STABLEHASH-EQ`. When the symbol `EQL` or the function `#'eql` is used as a `:TEST` argument, the value of the variable `CUSTOM:*EQL-HASHFUNCTION*` is used instead; this value must be one of `EXT:FASTHASH-EQL`, `EXT:STABLEHASH-EQL`. Similarly, when the symbol `EQUAL` or the function `#'equal` is used as a `:TEST` argument, the value of the variable `CUSTOM:*EQUAL-HASHFUNCTION*` is used instead; this value must be one of `EXT:FASTHASH-EQUAL`, `EXT:STABLEHASH-EQUAL`.

The `:WARN-IF-NEEDS-REHASH-AFTER-GC` argument, if true, causes a `WARNING` to be `SIGNAL`ed when an object is stored into the table which will force table reorganizations at the first access of the table after each garbage-collection. This keyword argument can be used to check whether `EXT:STABLEHASH-EQ` should be preferred over `EXT:FASTHASH-EQ` for a particular table. Use `HASH-TABLE-WARN-IF-NEEDS-REHASH-AFTER-GC` to check and `SETF` this parameter after the table has been created.

The `:INITIAL-CONTENTS` argument is an association list that is used to initialize the new hash table.

The `:REHASH-THRESHOLD` argument is ignored.

The `:WEAK` argument can take the following values:

`NIL` (default)
`:KEY`
`:VALUE`
`:KEY-AND-VALUE`
`:KEY-OR-VALUE`

and specifies whether the `HASH-TABLE` is weak: if the key, value, either or both are not accessible for the garbage-collection purposes, i.e., if they are only accessible via weak `HASH-TABLE`s and `EXT:WEAK-POINTER`s, it is garbage-collected and removed from the weak `HASH-TABLE`.

The `SETF`able predicate `EXT:HASH-TABLE-WEAK-P` checks whether the `HASH-TABLE` is weak.

Note that the only test that makes sense for weak hash tables are `EQ` and its variants `EXT:FASTHASH-EQ` and `EXT:STABLEHASH-EQ`.

Just like all other weak objects, weak `HASH-TABLE`s cannot be printed readably.

See also Section 31.7.9, “Weak Hash Tables”.

### 18.2.1. Interaction between `HASH-TABLE`s and garbage-collection

When a hash table contains keys to be compared by identity - such as `NUMBER`s in `HASH-TABLE`s with the `HASH-TABLE-TEST` `EQ`; or `CONS`es in tables which test with `EQ` or `EQL`; or `VECTOR`s in tables which test with `EQ`, `EQL` or `EQUAL`; or `STANDARD-OBJECT` or `STRUCTURE-OBJECT` instances in tables which test with `EQ`, `EQL`, `EQUAL` or `EQUALP`; - the hash code will in general depend on the object's address in memory. Therefore it will in general be invalidated after a garbage-collection, and the hash table's internal structure must be recomputed at the next table access.

While `:WARN-IF-NEEDS-REHASH-AFTER-GC` can help checking the efficiency of a particular `HASH-TABLE`, the variable `CUSTOM:*WARN-ON-HASHTABLE-NEEDING-REHASH-AFTER-GC*` achieves the same effect for all `HASH-TABLE`s in the system at once: when `CUSTOM:*WARN-ON-HASHTABLE-NEEDING-REHASH-AFTER-GC*` is true and a `HASH-TABLE` needs to be rehashed after a garbage-collection, a warning is issued that shows the inefficient `HASH-TABLE`.

What can be done to avoid the inefficiencies detected by these warnings?

1. In many cases you can solve the problem by using the `STABLEHASH` variant of the hash test.
2. In other cases, namely `STANDARD-OBJECT` or `STRUCTURE-OBJECT` instances, you can solve the problem by making the key object classes inherit from `EXT:STANDARD-STABLEHASH` or `EXT:STRUCTURE-STABLEHASH`, respectively.
3. In the remaining cases, you should store a hash key inside the object, of which you can guarantee uniqueness through your application (for example the ID of an object in a database, or the serial number of an object), and use this key as hash key instead of the original object.

## 18.3. Macro `EXT:DEFINE-HASH-TABLE-TEST`

You can define a new hash table test using the macro `EXT:DEFINE-HASH-TABLE-TEST`: `(`EXT:DEFINE-HASH-TABLE-TEST` test-name `test-function` `hash-function`)`, after which `name` can be passed as the `:TEST` argument to `MAKE-HASH-TABLE`. E.g.:

    (EXT:DEFINE-HASH-TABLE-TEST string STRING= SXHASH)
    ⇒ STRING
    (MAKE-HASH-TABLE :test 'string)
    ⇒ #S(HASH-TABLE :TEST (#<SYSTEM-FUNCTION STRING=> . #<SYSTEM-FUNCTION SXHASH>))

(which is not too useful because it is equivalent to an `EQUAL` `HASH-TABLE` but less efficient).

The fundamental requirement is that the `test-function` and `hash-function` are consistent:

    (FUNCALL test-function x y) ⇒
    (= (FUNCALL hash-function x) (FUNCALL hash-function y))

This means that the following definition:

    (EXT:DEFINE-HASH-TABLE-TEST number = SXHASH)	; broken!

is not correct because

    (= 1 1d0)
    ⇒ T	; same object!
    (= (SXHASH 1) (SXHASH 1d0))
    ⇒ NIL	; different buckets!

The correct way is, e.g.:

    (EXT:DEFINE-HASH-TABLE-TEST number = (LAMBDA (x) (SXHASH (COERCE x 'SHORT-FLOAT))))

### Note

Note that `COERCE`ing to a `SHORT-FLOAT` does not cons up fresh objects while `COERCE`ing to a `DOUBLE-FLOAT` does.

## 18.4. Function `HASH-TABLE-TEST`

Function `HASH-TABLE-TEST` returns either one of

`EXT:FASTHASH-EQ` | `EXT:FASTHASH-EQUAL`
`EXT:STABLEHASH-EQ` | `EXT:STABLEHASH-EQUAL`
`EXT:FASTHASH-EQL` | `EQUALP`
`EXT:STABLEHASH-EQL` |

(but not `EQ`, `EQL` nor `EQUAL` anymore), or, for `HASH-TABLE`s created with a user-defined `HASH-TABLE-TEST` (see macro `EXT:DEFINE-HASH-TABLE-TEST`), a `CONS` cell (`test-function` . `hash-function`).

## 18.5. Macro `EXT:DOHASH`

For iteration through a `HASH-TABLE`, a macro `EXT:DOHASH`, similar to `DOLIST`, can be used instead of `MAPHASH`:

    (EXT:DOHASH (key-var value-var hash-table-form [resultform])
      {declaration}*
      {tag|form}*)

`EXT:DOHASH` forms are iteration forms.

## Chapter 19. Filenames [chap-19]

For most operations, pathnames denoting files and pathnames denoting directories cannot be used interchangeably.

Platform Dependent: UNIX platform only.
  For example, `#P"foo/bar"` denotes the file `#P"bar"` in the directory `#P"foo"`, while `#P"foo/bar/"` denotes the subdirectory `#P"bar"` of the directory `#P"foo"`.
Platform Dependent: Win32 platform only.
  For example, `#P"foo\\bar"` denotes the file `#P"bar"` in the directory `#P"foo"`, while `#P"foo\\bar\\"` denotes the subdirectory `#P"bar"` of the directory `#P"foo"`.
Platform Dependent: Win32 and Cygwin platforms only.
  User variable `CUSTOM:*DEVICE-PREFIX*` controls translation between Cygwin pathnames (e.g., `#P"/cygdrive/c/gnu/clisp/"`) and native Win32 pathnames (e.g., `#P"C:\\gnu\\clisp\\"`) When it is set to `NIL`, no translations occur and the Cygwin port will not understand the native paths and the native Win32 port will not understand the Cygwin paths. When its value is a string, it is used by `PARSE-NAMESTRING` to translate into the appropriate platform-specific representation, so that on Cygwin, `(`PARSE-NAMESTRING` "c:/gnu/clisp/")` returns `#P"/cygdrive/c/gnu/clisp/"`, while on Win32 `(`PARSE-NAMESTRING` "/cygdrive/c/gnu/clisp/")` returns `#P"C:/gnu/clisp/"`. The initial value is `"cygdrive"`, you should edit `config.lisp` to change it.

This is especially important for the directory-handling functions.

Table 19.1. The minimum filename syntax that may be used portably

pathname | meaning
--- | ---
`"xxx"` | for a file with name `xxx`
`"xxx.yy"` | for a file with name `xxx` and type `yy`
`".yy"` | for a pathname with type `yy` and no name or with name `.yy` and no type, depending on the value of `CUSTOM:*PARSE-NAMESTRING-DOT-FILE*`.

Hereby `xxx` denotes 1 to 8 characters, and `yy` denotes 1 to 3 characters, each of which being either an alphanumeric character or the underscore #\_. Other properties of pathname syntax vary between operating systems.

## 19.1. Pathname Components [sec_19-2-1]

When a pathname is to be fully specified (no wildcards), that means that no `:WILD`, `:WILD-INFERIORS` is allowed, no wildcard characters are allowed in the strings, and `name` `EQ` `NIL` may not be allowed either.

### 19.1.1. Directory canonicalization

As permitted by the `MAKE-PATHNAME` specification, the `PATHNAME` directory component is canonicalized when the pathname is constructed:

1. `""` and `"."` are removed
2. `".."`, `"*"`, and `"**"` are converted to `:UP`, `:WILD` and `:WILD-INFERIORS`, respectively
3. patterns `foo/../` are collapsed

### 19.1.2. Platform-specific issues

Platform Dependent: UNIX platform only.

  Pathname components

  `host`
    always `NIL`
  `device`
    always `NIL`
  ``directory` = (`startpoint` . `subdirs`)`

    element | values | meaning
    --- | --- | ---
    `startpoint` | `:RELATIVE` | `:ABSOLUTE` |
    `subdirs` | `()` | `(`subdir` . `subdirs`)` |
    `subdir` | `:WILD-INFERIORS` | `**` or `...`, all subdirectories
    `subdir` | `SIMPLE-STRING`, may contain wildcard characters `"?"` and `"*"` (may also be specified as `:WILD`) |

  `name`
  `type`
    `NIL` or `SIMPLE-STRING`, may contain wildcard characters `"?"` and `"*"` (may also be specified as `:WILD`)
  `version`
    `NIL` or `:WILD` or `:NEWEST` (after merging the defaults)

  A UNIX filename is split into name and type.

  External notation: | `"server:sub1.typ/sub2.typ/name.typ"`
  using defaults: | `"sub1.typ/sub2.typ/name.typ"`
  or | `"name.typ"`
  or | `"sub1.typ/**/sub3.typ/x*.lisp"`
  or similar. |

Platform Dependent: Win32 platform only.

  Pathname components

  `host`
    `NIL` or `SIMPLE-STRING`, wildcard characters may occur but do not act as wildcards
  `device`
    `NIL` or `:WILD` or `A`|...|`Z`
  ``directory` = (`startpoint` . `subdirs`)`

    element | values | meaning
    --- | --- | ---
    `startpoint` | `:RELATIVE` | `:ABSOLUTE` |
    `subdirs` | `()` | `(`subdir` . `subdirs`)` |
    `subdir` | `:WILD-INFERIORS` | `**` or `...`, all subdirectories
    `subdir` | `SIMPLE-STRING`, may contain wildcard characters `"?"` and `"*"` (may also be specified as `:WILD`) |

  `name`
  `type`
    `NIL` or `SIMPLE-STRING`, may contain wildcard characters `"?"` and `"*"` (may also be specified as `:WILD`)
  `version`
    `NIL` or `:WILD` or `:NEWEST` (after merging the defaults)

  If `host` is non-`NIL`, `device` must be `NIL`.

  A Win32 filename is split into name and type.

  External notation: | `"A:\sub1.typ\sub2.typ\name.typ"`
  using defaults: | `"\sub1.typ\sub2.typ\name.typ"`
  or | `"name.typ"`
  or | `"*:\sub1.typ\**\sub3.typ\x*.lisp"`
  or similar. |

  Instead of `"\"` one may use `"/"`, as usual for DOS calls.

  If `host` is non-`NIL` and the `directory`'s `startpoint` is not `:ABSOLUTE`, `(`PARSE-NAMESTRING` (`NAMESTRING` `pathname`))` will not be the same as `pathname`.

Platform Dependent: UNIX, Win32 platforms only.
  The wildcard characters: `"*"` matches any sequence of characters, `"?"` matches any one character.

Name/type namestring split.

Platform Dependent: UNIX, Win32 platforms only.

  A filename is split into name and type according to the following rule:

  - if there is no `"."` in the filename, then the `name` is everything, `type` is `NIL`;
  - if there is a `"."`, then `name` is the part before and `type` the part after the last dot.

  - if the only `"."` is the first character, then the behavior depends on the value of the user variable `CUSTOM:*PARSE-NAMESTRING-DOT-FILE*` which can be either

    `:TYPE`
      `NIL` `name`, everything after the `"."` is the `type`; or
    `:NAME`
      `NIL` `type`, everything is the `name`

  ### Note

  Due to this name/type splitting rule, there are pathnames that cannot result from `PARSE-NAMESTRING`. To get a pathname whose type contains a dot or whose name contains a dot and whose type is `NIL`, `MAKE-PATHNAME` must be used. Example: `(`MAKE-PATHNAME` `:NAME` "foo.bar")`.

## 19.2. :UNSPECIFIC as a Component Value [sec_19-2-2-2-3]

The symbol `:UNSPECIFIC` is not permitted as a pathname component for any slot of any pathname. It is also illegal to pass it as an argument to `MAKE-PATHNAME`, although it is a legal argument (treated as `NIL`) to `USER-HOMEDIR-PATHNAME`.

The only use for `:UNSPECIFIC` is that it is returned by `PATHNAME-DEVICE` for `LOGICAL-PATHNAME`s, as required by [sec_19-3-2-1].

## 19.3. External notation

External notation of pathnames (cf. `PARSE-NAMESTRING` and `NAMESTRING`), of course without spaces, [,],{,}:

Platform Dependent: UNIX platform only.

  [ `"/"` ] | `"/"` denotes absolute pathnames
  { `name` `"/"` } | each `name` is a subdirectory
  [ `name` [`"."` `type`] ] | filename with type (extension)

  Name and type may be `STRING`s of any `LENGTH` (consisting of printing `CHARACTER`s, except `"/"`).

Platform Dependent: Win32 platform only.

  [ [`drivespec`] : ] | a letter `"*"`|`a`|...|`z`|`A`|...|`Z`
  { `name` [. `type`] \ } | each `name` is a subdirectory, `"\"` may be replaced by `"/"`
  [ `name` [. `type`] ] | filename with type (extension)

  Name and type may be `STRING`s of any `LENGTH` (consisting of printing `CHARACTER`s, except `"/"`, `"\"`, `":"`).

## 19.4. Logical Pathnames [sec_19-3]

No notes.

## 19.5. Miscellaneous

Pathname Designators. When `CUSTOM:*PARSE-NAMESTRING-ANSI*` is `NIL`, `SYMBOL` is also treated as a pathname designator, namely its `SYMBOL-NAME` is converted to the operating system's preferred pathname case.

Function `PATHNAME-MATCH-P`. `PATHNAME-MATCH-P` does not interpret missing components as wild.

### 19.5.1. Function `TRANSLATE-PATHNAME`

`TRANSLATE-PATHNAME` accepts three additional keyword arguments: `(`TRANSLATE-PATHNAME` `source` `from-wildname` `to-wildname` `&KEY` `:ALL` `:MERGE` `:ABSOLUTE`)`

If `:ALL` is specified and non-`NIL`, a list of all resulting pathnames, corresponding to all matches of `(`PATHNAME-MATCH-P` `source` `from-wildname`)`, is returned.

If `:MERGE` is specified and `NIL`, unspecified pieces of `to-pathname` are not replaced by corresponding pieces of `source`.

If `:ABSOLUTE` is specified and non-`NIL`, the returned pathnames are converted to absolute by merging in the current process' directory, therefore rendering pathnames suitable for the OS and external programs. So, to pass a pathname to an external program, you do `(`NAMESTRING` (`TRANSLATE-PATHNAME` `pathname` #P"" #P"" `:ABSOLUTE` `T`))` or `(`NAMESTRING` (`EXT:ABSOLUTE-PATHNAME` `pathname`))`.

### 19.5.2. Function `TRANSLATE-LOGICAL-PATHNAME`

`TRANSLATE-LOGICAL-PATHNAME` accepts an additional keyword argument `:ABSOLUTE`, similar to Section 19.5.1, “Function `TRANSLATE-PATHNAME`”.

### 19.5.3. Function `PARSE-NAMESTRING`

`(`PARSE-NAMESTRING` `string` `&OPTIONAL` `host` `defaults` `&KEY` `start` `end` `junk-allowed`)` returns a logical pathname only if `host` is a logical host or `host` is `NIL` and `defaults` is a `LOGICAL-PATHNAME`. To construct a logical pathname from a string, the function `LOGICAL-PATHNAME` can be used.

The [ANSI CL standard] behavior of recognizing logical pathnames when the `string` begins with some alphanumeric characters followed by a colon (#\:) can be very confusing (cf. `"c:/autoexec.bat"`, `"home:.clisprc"` and `"prep:/pub/gnu"`) and therefore is disabled by default. To enable the [ANSI CL standard] behavior, you should set `CUSTOM:*PARSE-NAMESTRING-ANSI*` to non-`NIL`. Note that this also disables treating `SYMBOL`s as pathname designators.

### 19.5.4. Function `MERGE-PATHNAMES`

`(`MERGE-PATHNAMES` `pathname` [`default-pathname`])` returns a logical pathname only if `default-pathname` is a `LOGICAL-PATHNAME`. To construct a logical pathname from a `STRING`, the function `LOGICAL-PATHNAME` can be used.

When both `pathname` and `default-pathname` are relative pathnames, the behavior depends on `CUSTOM:*MERGE-PATHNAMES-ANSI*`: when it is `NIL`, then CLISP retains its traditional behavior: `(`MERGE-PATHNAMES` #P"x/" #P"y/")` evaluates to `#P"x/"`

Rationale. `MERGE-PATHNAMES` is used to specify default components for pathnames, so there is some analogy between `(`MERGE-PATHNAMES` a b)` and `(`OR` a b)`. Obviously, putting in the same default a second time should do the same as putting it in once: `(`OR` a b b)` is the same as `(`OR` a b)`, so `(`MERGE-PATHNAMES` (`MERGE-PATHNAMES` a b) b)` should be the same as `(`MERGE-PATHNAMES` a b)`.

(This question actually does matter because in Common Lisp there is no distinction between “pathnames with defaults merged-in” and “pathnames with defaults not yet applied”.)

Now, `(`MERGE-PATHNAMES` (`MERGE-PATHNAMES` #P"x/" #P"y/") #P"y/")` and `(`MERGE-PATHNAMES` #P"x/" #P"y/")` are `EQUAL` in CLISP (when `CUSTOM:*MERGE-PATHNAMES-ANSI*` is `NIL`), but not in implementations that strictly follow the [ANSI CL standard]. In fact, the above twice-default = once-default rule holds for all pathnames in CLISP.

Conversely, when `CUSTOM:*MERGE-PATHNAMES-ANSI*` is non-`NIL`, the normal [ANSI CL standard] behavior is exhibited: `(`MERGE-PATHNAMES` #P"x/" #P"y/")` evaluates to `#P"y/x/"`.

Rationale. “merge” is merge and not or.

### 19.5.5. Function `LOAD-LOGICAL-PATHNAME-TRANSLATIONS`

When the `host` argument to `LOAD-LOGICAL-PATHNAME-TRANSLATIONS` is not a defined logical host yet, we proceed as follows:

1. If both environment variables `LOGICAL_HOST_`host`_FROM` and `LOGICAL_HOST_`host`_TO` exist, then their values define the map of the `host`.
2. If the environment variable `LOGICAL_HOST_`host`` exists, its value is read from, and the result is passed to `(`SETF` `LOGICAL-PATHNAME-TRANSLATIONS`)`.
3. Variable `CUSTOM:*LOAD-LOGICAL-PATHNAME-TRANSLATIONS-DATABASE*` is consulted. Its value should be a `LIST` of files and/or directories, which are searched for in the `CUSTOM:*LOAD-PATHS*`, just like for `LOAD`. When the element is a file, it is repeatedly `READ` from, Allegro CL-style, odd objects being host names and even object being their `LOGICAL-PATHNAME-TRANSLATIONS`. When the element is a directory, a file, named ``host`` or ``host`.host`, in that directory, is `READ` from once, CMUCL-style, the object read being the `LOGICAL-PATHNAME-TRANSLATIONS` of the `host`.

### 19.5.6. Function `EXT:ABSOLUTE-PATHNAME`

`(`EXT:ABSOLUTE-PATHNAME` `pathname`)` converts the `pathname` to a physical pathname, then - if its directory component is not absolute - converts it to an absolute pathname, by merging in the current process' directory. This is like `TRUENAME`, except that it does not verify that a file named by the `pathname` exists, not even that its directory exists. It does no filesystem accesses, except to determine the current directory. This function is useful when you want to save a pathname over time, or pass a pathname to an external program.

## Chapter 20. Files [chap-20]

## 20.1. Directory is not a file

CLISP has traditionally taken the view that a directory is a separate object and not a special kind of file, so whenever the standard says that a function operates on files without specifically mentioning that it also works on directories, CLISP `SIGNAL`s an `ERROR` when passed a directory.

CLISP provides separate directory functions, such as `EXT:DELETE-DIRECTORY`, `EXT:RENAME-DIRECTORY` et al.

You can use `DIRECTORY` or `EXT:PROBE-PATHNAME` to figure out whether a given namestring refers to a file or a directory.

### 20.1.1. Function `EXT:PROBE-PATHNAME`

Function `(`EXT:PROBE-PATHNAME` `pathname` `&KEY` (`:ERROR` `T`))` figures out whether the argument refers to an existing directory or an existing regular file, and returns 4 values if the filesystem object exists:

1. `TRUENAME`
2. `EXT:ABSOLUTE-PATHNAME`
3. `FILE-WRITE-DATE`
4. `POSIX:FILE-SIZE`

or `NIL` if it does not exist. E.g., if you have a file `file`, a directory `directory`, a symbolic link `link-file` pointing to `file` and a symbolic link `link-dir` pointing to `directory`, then

    (EXT:PROBE-PATHNAME #P"filename")
    ⇒ #P"/.../filename"
    ⇒ #P"/.../filename"
    ⇒ 3427467015
    ⇒ 3171976
    (EXT:PROBE-PATHNAME #P"filename/")
    ⇒ #P"/.../filename"
    ⇒ #P"/.../filename"
    ⇒ 3427467015
    ⇒ 3171976
    (EXT:PROBE-PATHNAME #P"directory")
    ⇒ #P"/.../directory/"
    ⇒ #P"/.../directory/"
    ⇒ 3426940352
    ⇒ 1024
    (EXT:PROBE-PATHNAME #P"directory/")
    ⇒ #P"/.../directory/"
    ⇒ #P"/.../directory/"
    ⇒ 3426940352
    ⇒ 1024
    (EXT:PROBE-PATHNAME #P"link-file")
    ⇒ #P"/.../filename"
    ⇒ #P"/.../link-file"
    ⇒ 3427467015
    ⇒ 3171976
    (EXT:PROBE-PATHNAME #P"link-file/")
    ⇒ #P"/.../filename"
    ⇒ #P"/.../link-file"
    ⇒ 3427467015
    ⇒ 3171976
    (EXT:PROBE-PATHNAME #P"link-dir")
    ⇒ #P"/.../directory/"
    ⇒ #P"/.../link-dir/"
    ⇒ 3426940352
    ⇒ 1024
    (EXT:PROBE-PATHNAME #P"link-dir/")
    ⇒ #P"/.../directory/"
    ⇒ #P"/.../link-dir/"
    ⇒ 3426940352
    ⇒ 1024

This function may also `SIGNAL`s an `ERROR` if, e.g., its argument resides under a tree for which you do not have sufficient access privileges; unless `:ERROR` is `NIL`, in which case `NIL` is returned instead.

## 20.2. File functions

### 20.2.1. Function `PROBE-FILE`

`PROBE-FILE` cannot be used to check whether a directory exists. Use functions `EXT:PROBE-DIRECTORY`, `EXT:PROBE-PATHNAME` or `DIRECTORY` for this.

### 20.2.2. Function `FILE-AUTHOR`

`FILE-AUTHOR` always returns `NIL`, because the operating systems CLISP is ported to do not store a file's author in the file system. Some operating systems, such as UNIX, have the notion of a file's owner, and some other Common Lisp implementations return the user name of the file owner. CLISP does not do this, because owner and author are not the same; in particular, authorship is preserved by copying, while ownership is not.

Use `OS:FILE-OWNER` to find the owner of the file. See also `OS:FILE-PROPERTIES` (Platform Dependent: Win32 platform only.).

### 20.2.3. Function `DELETE-FILE`

`(`DELETE-FILE` `pathname`)` deletes the pathname `pathname`, not its `TRUENAME`, and returns the absolute pathname it actually removed or `NIL` if `pathname` did not exist. When `pathname` points to a file which is currently open in CLISP, an `ERROR` is `SIGNAL`ed. To remove a directory, use `EXT:DELETE-DIRECTORY` instead.

### 20.2.4. Function `RENAME-FILE`

This functions accepts and extra keyword argument `:IF-EXISTS`. When it is `:ERROR` (the default), an `ERROR` is `SIGNAL`ed if the destination pathname names an existing file, otherwise (e.g., if it is `:OVERWRITE`) the destination file atomically overwritten.

When `CUSTOM:*ANSI*` is non-`NIL`, only the standard two arguments are accepted, and and `ERROR` is `SIGNAL`ed when the destination pathname names an existing file.

This function cannot operate on directories, use `EXT:RENAME-DIRECTORY` to rename a directory.

## 20.3. Directory functions

### 20.3.1. Function `EXT:PROBE-DIRECTORY`

`(`EXT:PROBE-DIRECTORY` `pathname`)` tests whether `pathname` exists and is a directory. It will, unlike `PROBE-FILE` or `TRUENAME`, not `SIGNAL` an `ERROR` if the parent directory of `pathname` does not exist.

### 20.3.2. Function `DIRECTORY`

`(`DIRECTORY` `&OPTIONAL` `pathname` `&KEY` :FULL :CIRCLE `:IF-DOES-NOT-EXIST`)` can run in two modes:

- If `pathname` contains no name or type component, a list of all matching directories is produced. E.g., `(`DIRECTORY` "/etc/*/")` lists all subdirectories in the directory `#P"/etc/"`.
- Otherwise a list of all matching files is returned. E.g., `(`DIRECTORY` "/etc/*")` lists all regular files in the directory `#P"/etc/"`.

If you want all the files and subdirectories in the current directory, you should use `(`NCONC` (`DIRECTORY` "*/") (`DIRECTORY` "*"))`. If you want all the files and subdirectories in all the subdirectories under the current directory (similar to the ls `-R` UNIX command), use `(`NCONC` (`DIRECTORY` "**/") (`DIRECTORY` "**/*"))`.

Keyword arguments accepted by `DIRECTORY`

`:FULL`
  If this argument is non-`NIL`, additional information is returned: for each matching file you get a `LIST` of at least four elements (`file-pathname` `file-truename` `file-write-date-as-decoded-time` `file-length`).
`:CIRCLE`
  If this argument is non-`NIL`, `DIRECTORY` avoids endless loops that may result from symbolic links.
`:IF-DOES-NOT-EXIST`

  This argument controls the treatment of links pointing to non-existent files and can take the following values:

  `:DISCARD` (default)
    discard the bad directory entries
  `:ERROR`
    an `ERROR` is `SIGNAL`ed on bad directory entries (this corresponds to the default behavior of `DIRECTORY` in CMU CL)
  `:KEEP`
    keep bad directory entries in the returned list (this roughly corresponds to the `(`DIRECTORY` ... `:TRUNAMEP` `NIL`)` call in CMU CL)
  `:IGNORE`
    Similar to `:DISCARD`, but also do not `SIGNAL` an `ERROR` when a directory is unaccessible (contrary to the [ANSI CL standard] specification).

### 20.3.3. Function `EXT:DIR`

`(`EXT:DIR` `&OPTIONAL` `pathname`)` is like `DIRECTORY`, but displays the pathnames instead of returning them. `(EXT:DIR)` shows the contents of the current directory.

### 20.3.4. Function `EXT:CD`

`(`EXT:CD` `pathname`)` sets the current working directory, `(`EXT:CD`)` returns it.

Platform Dependent: UNIX platform only.
  `(`EXT:CD` [`pathname`])` manages the current directory.
Platform Dependent: Win32 platform only.
  `(`EXT:CD` [`pathname`])` manages the current device and the current directory.

### 20.3.5. Function `EXT:DEFAULT-DIRECTORY`

`(`EXT:DEFAULT-DIRECTORY`)` is equivalent to `(`EXT:CD`)`. `(`SETF` (`EXT:DEFAULT-DIRECTORY`) `pathname`)` is equivalent to `(`EXT:CD` `pathname`)`, except for the return value.

### 20.3.6. Function `EXT:MAKE-DIRECTORY`

`(`EXT:MAKE-DIRECTORY` `directory`)` creates a new subdirectory.

### 20.3.7. Function `EXT:DELETE-DIRECTORY`

`(`EXT:DELETE-DIRECTORY` `directory`)` removes an (empty) subdirectory.

### 20.3.8. Function `EXT:RENAME-DIRECTORY`

`(`EXT:RENAME-DIRECTORY` `old-directory` `new-directory`)` renames a subdirectory to a new name.

## Chapter 21. Streams [chap-21]

## 21.1. Interactive Streams [sec_21-1-1-1-3]

Interactive streams are those whose next input might depend on a prompt one might output.

### 21.1.1. Initialization of Standard Streams

When run interactively, CLISP creates a single “terminal” `STREAM` and binds `*TERMINAL-IO*` to it. All other standard streams (`*STANDARD-INPUT*`, `*STANDARD-OUTPUT*` `*ERROR-OUTPUT*`, `*TRACE-OUTPUT*`, `*QUERY-IO*`, `*DEBUG-IO*`) are `SYNONYM-STREAM`s pointing to `*TERMINAL-IO*`. This has the benefit of avoiding unwanted blank lines from `FRESH-LINE`, see Section 21.6, “Newline Convention”.

However, there may be situations, especially in batch mode, when one wants to use a C-style i/o where `*STANDARD-OUTPUT*` and `*ERROR-OUTPUT*` point to different OS file descriptor so that they can be redirected to files in the command line and examined separately. Often CLISP can detect such situations (`stdout` and `stderr` not being the terminal) and handle them just as expected. However, there may be cases when one needs to do something like:

    (SETQ *STANDARD-INPUT* (EXT:MAKE-STREAM :INPUT)
          *STANDARD-OUTPUT* (EXT:MAKE-STREAM :OUTPUT :BUFFERED T)
          *ERROR-OUTPUT* (EXT:MAKE-STREAM :ERROR :BUFFERED T))

in the script or init function.

## 21.2. Terminal interaction

List of Examples

21.1. Dialog with user using completion

See also Section 32.1, “Random Screen Access”.

### 21.2.1. Command line editing with GNU readline

#### Platform Dependent: Only in CLISP linked against the GNU readline library.

List of Examples

21.1. Dialog with user using completion

Input through `*TERMINAL-IO*` uses the GNU readline library. Arrow keys can be used to move within the input history. The TAB key completes the `SYMBOL` name or `PATHNAME` that is being typed. See readline user manual for general details and TAB key for CLISP-specific extensions.

### Warning

The GNU readline library is not used (even when CLISP is linked against it) if the `stdin` and `stdout` do not both refer to the same terminal. This is determined by the function `stdio_same_tty_p` in file `src/stream.d`. In some exotic cases, e.g., when running under gdb in an rxvt window under Cygwin, this may be determined incorrectly.

See also Section 33.5, “Advanced Readline and History Functionality”.

#### Extending completion

Variable `CUSTOM:*COMPLETION*`. The value should be a `FUNCTION` of 3 arguments: `string`, `start` and `end`, which bound the text to be completed. The return value should be the list, whose `FIRST` is the immediate replacement for the already typed text and `REST` is all the possible completions. If no completions are available, return `NIL`.

Function `EXT:MAKE-COMPLETION`. Given a `LIST` of all valid inputs, return a valid value for `CUSTOM:*COMPLETION*`.

Function `EXT:LONGEST-COMMON-PREFIX`. Given a `LIST` of `VECTOR`s, return the `VECTOR` which is their longest common prefix. `VECTOR` elements are compared using the `:TEST` argument. Useful when writing your own `CUSTOM:*COMPLETION*` functions.

Example 21.1. Dialog with user using completion

    (defun read-user-line (prompt completions)
      (princ prompt *query-io*)
      (force-output *query-io*)
      (let ((custom:*completion* (ext:make-completion completions)))
        (read-line *query-io*)))
    (read-user-line "??? " '("a" "z123" "z135" "b" "abcd"))
    ⇒ ??? ab TAB
    ⇒ ??? abcd
    (read-user-line "??? " '("a" "z123" "z135" "b" "abcd"))
    ⇒ ??? TAB TAB
    ⇒ a abcd b z123 z135
    ⇒ ??? z TAB
    ⇒ ??? z1TAB TAB
    ⇒ z123 z135

To force the user to select one of the pre-specified inputs you need to do something like this:

    (defun read-user-line (prompt)
      (princ prompt *query-io*)
      (force-output *query-io*)
      (read-line *query-io*))
    (defun read-user-option (prompt options)
      (loop
        :with custom:*completion* = (ext:make-completion options)
        :for option = (read-user-line prompt)
        :when (find option options :text #'string=)
        :return options
        :do (format *query-io* "Invalid option ~S, please try again~%" option)))

#### Linking against GNU readline

For CLISP to use GNU readline it has to be detected by the configure process.

- If you run it as

      $ ./configure --with-readline

  it will fail if it cannot find a valid modern GNU readline installation.

- If you use the option `--without-readline`, it will not even try to find GNU readline.
- The default behavior (`--with-readline=default`) is to use GNU readline if it is found and link CLISP without it otherwise.

You can find out whether GNU readline has been detected by running

    $ grep HAVE_READLINE config.h

in your build directory.

### 21.2.2. Macro `EXT:WITH-KEYBOARD`

#### Platform Dependent: UNIX, Win32 platforms only.

`*TERMINAL-IO*` is not the only stream that communicates directly with the user: During execution of the body of a `(`EXT:WITH-KEYBOARD` . `body`)` form, `EXT:*KEYBOARD-INPUT*` is the `STREAM` that reads the keystrokes from the keyboard. It returns every keystroke in detail as an `SYS::INPUT-CHARACTER` with the following slots (see Section 13.4.1, “Input Characters” for accessing them):

`char`

  the `CHARACTER` for standard keys (accessed with `CHARACTER`)

  ### Note

  For non-standard keys `CHARACTER` `SIGNAL`s an `ERROR`, use `EXT:CHAR-KEY`:

      (EXT:WITH-KEYBOARD
       (LOOP :for char = (READ-CHAR EXT:*KEYBOARD-INPUT*)
         :for key = (OR (EXT:CHAR-KEY char) (CHARACTER char))
         :do (PRINT (LIST char key))
         :when (EQL key #\Space) :return (LIST char key)))

`key`

  the key name, for non-standard keys (accessed with `EXT:CHAR-KEY`):

  Platform Dependent: UNIX, Win32 platforms only.

    key | value
    --- | ---
    F1..F12 | `:F1`..`:F12`
    Insert | `:INSERT`
    Delete | `:DELETE`
    Home | `:HOME`
    End | `:END`
    Center | `:CENTER`
    PgUp | `:PGUP`
    PgDn | `:PGDN`
    Arrow keys | `:LEFT` `:RIGHT` `:UP` `:DOWN`

`bits`
  `:HYPER`
    (Platform Dependent: Win32 platform only.) if a non-standard key. These keys are: [Win32]: Function keys, cursor keypads, numeric keypad.
  `:SUPER`
    (Platform Dependent: Win32 platform only.) if pressed together with Shift key(s) and if the keystroke would have been different without Shift.
  `:CONTROL`
    if pressed together with the Control key.
  `:META`
    (Platform Dependent: Win32 platform only.) if pressed together with the Alternate key.
`font`
  Always `0`.

This keyboard input is not echoed on the screen. During execution of a `(`EXT:WITH-KEYBOARD` . `body`)` form, no input from `*TERMINAL-IO*` or any synonymous stream should be requested.

### Warning

Since `SYS::INPUT-CHARACTER` is not a subtype of `CHARACTER`, `READ-LINE` on `EXT:*KEYBOARD-INPUT*` is illegal.

## 21.3. Binary Input and Output

### 21.3.1. Binary input, `READ-BYTE`, `EXT:READ-INTEGER` & `EXT:READ-FLOAT`

The function `(`EXT:READ-INTEGER` `stream` `element-type` `&OPTIONAL` `ENDIANNESS` `eof-error-p` `eof-value`)` reads a multi-byte `INTEGER` from `stream`, which should be a `STREAM` with `STREAM-ELEMENT-TYPE` `(`UNSIGNED-BYTE` 8)`. `element-type` should be type equivalent to `(`UNSIGNED-BYTE` `n`)`, where `n` is a multiple of 8.

`(`EXT:READ-INTEGER` `stream` `element-type`)` is like `(`READ-BYTE` `stream`)` if `stream`'s `STREAM-ELEMENT-TYPE` were set to `element-type`, except that `stream`'s `FILE-POSITION` will increase by `n`/8 instead of 1.

Together with `(`SETF` `STREAM-ELEMENT-TYPE`)`, this function permits mixed character/binary input from a stream.

The function `(`EXT:READ-FLOAT` `stream` `element-type` `&OPTIONAL` `ENDIANNESS` `eof-error-p` `eof-value`)` reads a floating-point number in IEEE 754 binary representation from `stream`, which should be a `STREAM` with `STREAM-ELEMENT-TYPE` `(`UNSIGNED-BYTE` 8)`. `element-type` should be type equivalent to `SINGLE-FLOAT` or `DOUBLE-FLOAT`.

Endianness. `ENDIANNESS` can be `:LITTLE` or `:BIG`. The default is `:LITTLE`, which corresponds to the `READ-BYTE` behavior in CLISP.

### 21.3.2. Binary output, `WRITE-BYTE`, `EXT:WRITE-INTEGER` & `EXT:WRITE-FLOAT`

The function `(`EXT:WRITE-INTEGER` `integer` `stream` `element-type` `&OPTIONAL` `ENDIANNESS`)` writes a multi-byte `INTEGER` to `stream`, which should be a `STREAM` with `STREAM-ELEMENT-TYPE` `(`UNSIGNED-BYTE` 8)`. `element-type` should be type equivalent to `(`UNSIGNED-BYTE` `n`)`, where `n` is a multiple of 8.

`(`EXT:WRITE-INTEGER` `integer` `stream` `element-type`)` is like `(`WRITE-BYTE` `integer` `stream`)` if `stream`'s `STREAM-ELEMENT-TYPE` were set to `element-type`, except that `stream`'s `FILE-POSITION` will increase by `n`/8 instead of 1.

Together with `(`SETF` `STREAM-ELEMENT-TYPE`)`, this function permits mixed character/binary output to a `STREAM`.

The function `(`EXT:WRITE-FLOAT` `float` `stream` `element-type` `&OPTIONAL` `ENDIANNESS`)` writes a floating-point number in IEEE 754 binary representation to `stream`, which should be a `STREAM` with `STREAM-ELEMENT-TYPE` `(`UNSIGNED-BYTE` 8)`. `element-type` should be type equivalent to `SINGLE-FLOAT` or `DOUBLE-FLOAT`.

## 21.4. Bulk Input and Output

### 21.4.1. Bulk Input

In addition to `READ-SEQUENCE`, the following two functions are provided:

`EXT:READ-BYTE-SEQUENCE` performs multiple `READ-BYTE` operations:

  `(`EXT:READ-BYTE-SEQUENCE` `sequence` `stream` `&KEY` `:START` `:END` :NO-HANG :INTERACTIVE)` fills the subsequence of `sequence` specified by `:START` and `:END` with `INTEGER`s consecutively read from `stream`. It returns the index of the first element of `sequence` that was not updated (= `end` or < `end` if the `stream` reached its end). When `no-hang` is non-`NIL`, it does not block: it treats input unavailability as `end-of-stream`. When `no-hang` is `NIL` and `interactive` is non-`NIL`, it can block for reading the first byte but does not block for any further bytes.

  This function is especially efficient if `sequence` is a `(`VECTOR` (`UNSIGNED-BYTE` 8))` and `stream` is a file/pipe/socket `STREAM` with `STREAM-ELEMENT-TYPE` `(`UNSIGNED-BYTE` 8)`.

`EXT:READ-CHAR-SEQUENCE` performs multiple `READ-CHAR` operations:

  `(`EXT:READ-CHAR-SEQUENCE` `sequence` `stream` `&KEY` `:START` `:END`)` fills the subsequence of `sequence` specified by `:START` and `:END` with characters consecutively read from `stream`. It returns the index of the first element of `sequence` that was not updated (= `end` or < `end` if the `stream` reached its end).

  This function is especially efficient if `sequence` is a `STRING` and `stream` is a file/pipe/socket `STREAM` with `STREAM-ELEMENT-TYPE` `CHARACTER` or an input `STRING-STREAM`.

### 21.4.2. Bulk Output

In addition to `WRITE-SEQUENCE`, the following two functions are provided:

`EXT:WRITE-BYTE-SEQUENCE` performs multiple `WRITE-BYTE` operations:

  `(`EXT:WRITE-BYTE-SEQUENCE` `sequence` `stream` `&KEY` `:START` `:END` :NO-HANG :INTERACTIVE)` outputs the `INTEGER`s of the subsequence of `sequence` specified by `:START` and `:END` to `stream`. When `no-hang` is non-`NIL`, does not block. When `no-hang` is `NIL` and `interactive` is non-`NIL`, it can block for writing the first byte but does not block for any further bytes. Returns two values: `sequence` and the index of the first byte that was not output.

  This function is especially efficient if `sequence` is a `(`VECTOR` (`UNSIGNED-BYTE` 8))` and `stream` is a file/pipe/socket `STREAM` with `STREAM-ELEMENT-TYPE` `(`UNSIGNED-BYTE` 8)`.

`EXT:WRITE-CHAR-SEQUENCE` performs multiple `WRITE-CHAR` operations:

  `(`EXT:WRITE-CHAR-SEQUENCE` `sequence` `stream` `&KEY` `:START` `:END`)` outputs the characters of the subsequence of `sequence` specified by `:START` and `:END` to `stream`. Returns the `sequence` argument.

  This function is especially efficient if `sequence` is a `STRING` and `stream` is a file/pipe/socket `STREAM` with `STREAM-ELEMENT-TYPE` `CHARACTER`.

### 21.4.3. Rationale

The rationale for `EXT:READ-CHAR-SEQUENCE`, `EXT:READ-BYTE-SEQUENCE`, `EXT:WRITE-CHAR-SEQUENCE` and `EXT:WRITE-BYTE-SEQUENCE` is that some `STREAM`s support both character and binary i/o, and when you read into a `SEQUENCE` that can hold both (e.g., `LIST` or `SIMPLE-VECTOR`) you cannot determine which kind of input to use. In such situation `READ-SEQUENCE` and `WRITE-SEQUENCE` `SIGNAL` an `ERROR`, while `EXT:READ-CHAR-SEQUENCE`, `EXT:READ-BYTE-SEQUENCE`, `EXT:WRITE-CHAR-SEQUENCE` and `EXT:WRITE-BYTE-SEQUENCE` work just fine.

## 21.5. Non-Blocking Input and Output

In addition to the standard functions `LISTEN` and `READ-CHAR-NO-HANG`, CLISP provides the following functionality facilitating non-blocking input and output, both binary and character.

`(`EXT:READ-CHAR-WILL-HANG-P` `stream`)`

  `EXT:READ-CHAR-WILL-HANG-P` queries the stream's input status. It returns `NIL` if `READ-CHAR` and `PEEK-CHAR` with a `peek-type` of `NIL` will return immediately. Otherwise it returns `T`. (In the latter case the standard `LISTEN` function would return `NIL`.)

  Note the difference with `(`NOT` (`LISTEN` `stream`))`: When the `end-of-stream` is reached, `LISTEN` returns `NIL`, whereas `EXT:READ-CHAR-WILL-HANG-P` returns `NIL`.

  Note also that `EXT:READ-CHAR-WILL-HANG-P` is not a good way to test for `end-of-stream`: If `EXT:READ-CHAR-WILL-HANG-P` returns `T`, this does not mean that the `stream` will deliver more characters. It only means that it is not known at this moment whether the `stream` is already at `end-of-stream`, or will deliver more characters.

`(`EXT:READ-BYTE-LOOKAHEAD` `stream`)`
  To be called only if `stream`'s `STREAM-ELEMENT-TYPE` is `(`UNSIGNED-BYTE` 8)` or `(`SIGNED-BYTE` 8)`. Returns `T` if `READ-BYTE` would return immediately with an `INTEGER` result. Returns `:EOF` if the `end-of-stream` is already known to be reached. If `READ-BYTE`'s value is not available immediately, returns `NIL` instead of waiting.
`(`EXT:READ-BYTE-WILL-HANG-P` `stream`)`
  To be called only if `stream`'s `STREAM-ELEMENT-TYPE` is `(`UNSIGNED-BYTE` 8)` or `(`SIGNED-BYTE` 8)`. Returns `NIL` if `READ-BYTE` will return immediately. Otherwise it returns true.
`(`EXT:READ-BYTE-NO-HANG` `stream` `&OPTIONAL` `eof-error-p` `eof-value`)`
  To be called only if `stream`'s `STREAM-ELEMENT-TYPE` is `(`UNSIGNED-BYTE` 8)` or `(`SIGNED-BYTE` 8)`. Returns an `INTEGER` or does `end-of-stream` handling, like `READ-BYTE`, if that would return immediately. If `READ-BYTE`'s value is not available immediately, returns `NIL` instead of waiting.

### `LISTEN` on binary streams

The [ANSI CL standard] specification for `LISTEN` mentions “character availability” as the criterion that determines the return value. Since a `CHARACTER` is never available on a binary `STREAM` (i.e., a stream with `STREAM-ELEMENT-TYPE` being a subtype of `INTEGER`), `LISTEN` returns `NIL` for such streams. (You can use `SOCKET:SOCKET-STATUS` to check binary streams). Any other behavior would be hard to make consistent: consider a bivalent stream, i.e., a `STREAM` that can be operated upon by both `READ-CHAR` and `READ-BYTE`. What should `LISTEN` return on such a stream if what is actually available on the stream at the moment is only a part of a multi-byte character? Right now one can use first `SOCKET:SOCKET-STATUS` to check if anything at all is available and then use `LISTEN` to make sure that a full `CHARACTER` is actually there.

## 21.6. Newline Convention

### 21.6.1. Should programs output a newline before or after each line of output?

The answer is complicated. There is an antagonism between the “old Lisp way” of outputting a newline before the line's contents (exemplified by the functions `PRINT` and `PPRINT`) and the “Unix way” of outputting a newline after the line's contents. Which one is “right”?

A newline convention is, by definition, a consistent way to use the `TERPRI` and `FRESH-LINE` functions or - in `FORMAT` notation - `~%` and `~&` directives in such a way that the resulting output is properly subdivided into lines.

Three newline conventions are conceivable:

1. Print a newline before the line, and nothing after it. As a format string: “~%First line.~%Second line.”
2. Print a newline if needed before the line, and a newline always after it. As a format string: “~&First line.~%Second line.~%”
3. Print nothing before the line, and a newline always after it. As a format string: “First line.~%Second line.~%”

The most important criterion is interoperability. Two newline conventions are interoperable if, when parts of a program use one of the convention and other parts of the program use the other conventions, lines are still properly separated. It is easily seen that A and B are interoperable, B and C are interoperable as well, but A and C are not interoperable: When an output with convention A is followed by output in convention C, two lines are appended without a line separator. This should not happen.

Therefore, in what follows, we consider five kinds of programs:

- A: using convention A exclusively,
- AB: mixing conventions A and B,
- B: using convention B exclusively,
- BC: mixing conventions B and C,
- C: using convention C exclusively.

Which of these five kinds of programs operation is satisfactory? Let us consider different criteria:

1. Do extra blank lines occur during normal operation?
2. What happens if `FRESH-LINE` prints a newline when it is not needed, i.e. when it cannot tell for sure whether the current column is 0? (This situation happens, for example, when logging to a file: After the user has entered a line interactively, the column on screen is 0, but since the input has not been echoed in the log file, the column in the log file is usually not 0, and `FRESH-LINE` must output a newline. Then a blank line is visible on the screen.)
3. What happens if `FRESH-LINE` omits a newline when it would be needed? (This is more rare, but can happen, for example, when standard output and standard error are different streams but are joined outside the Lisp implementation, at the OS level. Such as in lisp | cat.)

4. Is it possible to reliably output a blank line before or after a paragraph of text? I.e. what happens with

   1. 1. “~%~%First line.~%Second line.”
      2. “~%First line.~%Second line.~%”
   2. 1. “~&~%First line.~%Second line.~%”
      2. “~&First line.~%Second line.~%~%”
   3. 1. “~%First line.~%Second line.~%”
      2. “First line.~%Second line.~%~%”
5. Is it possible to optimize away blank lines? I.e. is it possible to avoid a blank line even though another piece of code uses one of A1 ... C2, without risking that adjacent lines be unseparated?

### 21.6.2. Analysis

1. - A: No extra blank lines.
   - AB: An extra blank line each time one switches from convention B to A.
   - B: No extra blank lines.
   - BC: No extra blank lines.
   - C: No extra blank lines.
2. - A: No extra blank lines.
   - AB: Blank lines can occur when convention B is used.
   - B: Blank lines can occur.
   - BC: Blank lines can occur when convention B is used.
   - C: No extra blank lines.
3. - A: No problem.
   - AB: Lines can be unseparated when one switches from convention A to B.
   - B: No problem.
   - BC: No problem.
   - C: No problem.
4. - A: No problem.
   - AB: The blank line is omitted when using A2 before switching to B.
   - B: No problem.
   - BC: No problem.
   - C: No problem.
5. - A: Yes, using “~&First line.~%Second line.” eats a previous blank line.
   - AB: Not really: Using “~&First line.~%Second line.” may eat a previous blank line or a following blank line, but you cannot know in advance which one.
   - B: Yes, using “~&First line.~%Second line.” eats a following blank line.
   - BC: Impossible.
   - C: Impossible. To optimize blank lines in case C would require the opposite of `FRESH-LINE`, namely a conditional newline that is annullated if the next output on the stream will be a newline. (`EXT:ELASTIC-NEWLINE`, see below.)

### 21.6.3. Conclusion

Each approach has its advantages and disadvantages.

When used globally (i.e. no interoperability requirements), A, B, C can be compared as follows:

- A and C are equally perfect if eating blank lines is not a requirement.
- If eating blank lines is desirable, A is perfect.
- B is not so good, because it is suboptimal in case 2.

For CLISP built-ins, however, the interoperability requirement with both A and C is a major requirement. Therefore we have to choose B, and accept the drawbacks:

- AB: An extra blank line each time one switches from convention B to A.
- B: When logging to a file, blank lines can occur.
- AB: When joining two output streams into one, lines can be unseparated.
- AB: Blank lines after a paragraph can be eaten by CLISP.
- AB: Optimizing blank lines is not really possible.

And to minimize the drawbacks, we recommend the user programs to use approach B or C, but not A.

Another drawback of B is, however, that in interactive sessions the cursor is nearly always positioned at the beginning of a line, pointing the user's focus to the wrong point and taking away a screen line.

### 21.6.4. Solution

To solve this, we introduce the concept of an elastic newline, output by the function `EXT:ELASTIC-NEWLINE`. This is the converse of `FRESH-LINE`: It waits for the next character and outputs a newline when the next character is not a newline; then the next character is processed normally. As a `FORMAT` directive, we write it `~.`. `EXT:ELASTIC-NEWLINE` followed by `FRESH-LINE` leads to exactly one newline always.

Elastic newline leads to a slightly different newline convention:

- B': Print a newline if needed before the line, and a newline if needed after it. As a format string: “~&First line.~%Second line.~.”

The five programs being considered are now:

- A: using convention A exclusively,
- AB': mixing conventions A and B',
- B': using convention B' exclusively,
- B'C: mixing conventions B' and C,
- C: using convention C exclusively,

### 21.6.5. Elastic Newline Analysis

1. - A: No extra blank lines.
   - AB': No extra blank lines.
   - B': No extra blank lines.
   - B'C: No extra blank lines.
   - C: No extra blank lines.
2. - A: No extra blank lines.
   - AB': Blank lines can occur when convention B' is used.
   - B': Blank lines can occur.
   - B'C: Blank lines can occur when convention B' is used.
   - C: No extra blank lines.
3. - A: No problem.
   - AB': Lines can be unseparated when one switches from convention A to B'.
   - B': Lines can be unseparated when one switches from one stream to another without performing a `FORCE-OUTPUT`. This is a general problem with buffered streams; CLISP's `FRESH-LINE` contains a workaround that is limited to `*STANDARD-OUTPUT*` and `*ERROR-OUTPUT*`.
   - B'C: No problem.
   - C: No problem.
4. - A: No problem.
   - AB': The blank line is omitted when using A2 before switching to B' or when using B2 before switching to A.
   - B': No problem.
   - B'C: No problem.
   - C: No problem.
5. - A: Yes, using “~&First line.~%Second line.” eats a previous blank line.
   - AB': Not really: Using “~&First line.~%Second line.” may eat a previous blank line or a following blank line, but you cannot know in advance which one.
   - B': Yes, using “~&First line.~%Second line.” eats a following blank line.
   - B'C: Impossible.
   - C: Yes, using “First line.~%Second line.~.” eats a following blank line.

Now criterium 1 is satisfied perfectly. We therefore choose B', not B, for use inside CLISP, and programs can use either A or C without problems during normal operation.

## 21.7. Function `STREAM-EXTERNAL-FORMAT`

`STREAM-EXTERNAL-FORMAT` is `SETF`able: `(`SETF` (`STREAM-EXTERNAL-FORMAT` `stream` [`direction`]) `encoding`)`, `direction` can be `:INPUT`, `:OUTPUT`, or `NIL`. If no `direction` is given, the operation is nonrecursive.

This will not work on `*TERMINAL-IO*` et al, use `CUSTOM:*TERMINAL-ENCODING*` instead.

## 21.8. Function `STREAM-ELEMENT-TYPE`

`STREAM-ELEMENT-TYPE` is `SETF`able. The `STREAM-ELEMENT-TYPE` of `STREAM`s created by the functions `OPEN`, `EXT:MAKE-PIPE-INPUT-STREAM` `EXT:MAKE-PIPE-OUTPUT-STREAM`, `EXT:MAKE-PIPE-IO-STREAM`, `SOCKET:SOCKET-ACCEPT`, `SOCKET:SOCKET-CONNECT` can be modified, if the old and the new `STREAM-ELEMENT-TYPE`s are either

- both equivalent to `CHARACTER` or `(`UNSIGNED-BYTE` 8)` or `(`SIGNED-BYTE` 8)`; or
- both equivalent to `(`UNSIGNED-BYTE` `n`)` or `(`SIGNED-BYTE` `n`)`, with the same `n`.

Functions `STREAM-ELEMENT-TYPE` and `(`SETF` `STREAM-ELEMENT-TYPE`)` are `GENERIC-FUNCTION`s, see Chapter 30, Gray streams.

### Warning

CLISP expects to be able to do `CHARACTER` i/o on standard streams like `*TERMINAL-IO*`, `*STANDARD-OUTPUT*`, `*STANDARD-INPUT*`, `*ERROR-OUTPUT*`, `*QUERY-IO*` et al, thus it is a very bad idea to change their `STREAM-ELEMENT-TYPE` even when you can. Use `EXT:MAKE-STREAM` instead, see Section 21.8.1, “Binary input from `*STANDARD-INPUT*`”.

### 21.8.1. Binary input from `*STANDARD-INPUT*`

Note that you cannot change `STREAM-ELEMENT-TYPE` for some built-in streams, such as terminal streams, which is normally the value of `*TERMINAL-IO*`. Since `*STANDARD-INPUT*` normally is a `SYNONYM-STREAM` pointing to `*TERMINAL-IO*`, you cannot use `READ-BYTE` on it.

Since CGI (Common Gateway Interface) provides the form data for METHOD="POST" on the `stdin`, and the server will not send you an `end-of-stream` on the end of the data, you will need to use `(`EXT:GETENV` `"CONTENT_LENGTH"`)` to determine how much data you should read from `stdin`. CLISP will detect that `stdin` is not a terminal and create a regular `FILE-STREAM` which can be passed to `(`SETF` `STREAM-ELEMENT-TYPE`)`. To test this functionality interactively, you will need to open the standard input in the binary mode:

    (let ((buf (MAKE-ARRAY (PARSE-INTEGER (EXT:GETENV "CONTENT_LENGTH"))
                           :element-type '(UNSIGNED-BYTE 8))))
      (WITH-OPEN-STREAM (in (EXT:MAKE-STREAM :INPUT :ELEMENT-TYPE '(UNSIGNED-BYTE 8)))
        (READ-SEQUENCE buf in))
      buf)

## 21.9. Function `EXT:MAKE-STREAM`

Function `EXT:MAKE-STREAM` creates a Lisp stream out of an OS file descriptor: `(`EXT:MAKE-STREAM` `object` `&KEY` `:DIRECTION` `:ELEMENT-TYPE` `:EXTERNAL-FORMAT` `:BUFFERED`)`

`object` designates an OS handle (a file descriptor), and should be one of the following:

number
  denotes the file descriptor of this value
`:INPUT`
  denotes CLISP process standard input, that is, the file descriptor corresponding to `stdin` (0 on UNIX)
`:OUTPUT`
  denotes CLISP process standard output, that is, the file descriptor corresponding to `stdout` (1 on UNIX)
`:ERROR`
  denotes CLISP process error output, that is, the file descriptor corresponding to `stderr` (2 on UNIX)
`STREAM`
  denotes the handle of this stream, which should be a `FILE-STREAM` or a `SOCKET:SOCKET-STREAM`

### Beware of buffering!

When there are several Lisp `STREAM`s backed by the same OS file descriptor, the behavior may be highly confusing when some of the Lisp streams are `:BUFFERED`. Use `FORCE-OUTPUT` for output `STREAM`s, and bulk input for input `STREAM`s.

The handle is duplicated (with `dup`), so it is safe to `CLOSE` a `STREAM` returned by `EXT:MAKE-STREAM`.

## 21.10. Function `FILE-POSITION`

`FILE-POSITION` works on any `FILE-STREAM`.

Platform Dependent: Win32 platform only.
  When a #\Newline is output to (respectively input from) a `FILE-STREAM`, its file position is increased by 2 since #\Newline is encoded as CR/LF in the file.

## 21.11. Function `EXT:ELASTIC-NEWLINE`

The function `(`EXT:ELASTIC-NEWLINE` [`stream`])` is like `FRESH-LINE` but the other way around: It outputs a conditional newline on `stream`, which is canceled if the next output on `stream` happens to be a newline. More precisely, it causes a newline to be output right before the next character is written on `stream`, if this character is not a newline. The newline is also output if the next operation on the stream is `FRESH-LINE`, `FINISH-OUTPUT`, `FORCE-OUTPUT` or `CLOSE`.

The functionality of `EXT:ELASTIC-NEWLINE` is also available through the `FORMAT` directive `~.`.

A technique for avoiding unnecessary blank lines in output is to begin each chunk of output with a call to `FRESH-LINE` and to terminate it with a call to `EXT:ELASTIC-NEWLINE`.

See also Section 21.6, “Newline Convention”.

## 21.12. Function `OPEN`

`OPEN` accepts an additional keyword `:BUFFERED`.

The acceptable values for the arguments to the file/pipe/socket `STREAM` functions

`:ELEMENT-TYPE`

  types equivalent to `CHARACTER` or `(`UNSIGNED-BYTE` `n`)`, `(`SIGNED-BYTE` `n`)`; if the stream is to be un`:BUFFERED`, `n` must be a multiple of 8.

  If `n` is not a multiple of 8, CLISP will use the specified number of bits for i/o, and write the file length (as a number of `n`-bit bytes) in the preamble.

  This is done to ensure the input/output consistency: suppose you open a file with `:ELEMENT-TYPE` of `(`UNSIGNED-BYTE` 3)` and write 7 bytes (i.e., 21 bit) there. The underlying OS can do input/output only in whole 8-bit bytes. Thus the OS will report the size of the file as 3 (8-bit) bytes. Without the preamble CLISP will have no way to know how many 3-bit bytes to read from this file - 6, 7 or 8.

  See also Section 21.8, “Function `STREAM-ELEMENT-TYPE`”.

`:EXTERNAL-FORMAT`

  `EXT:ENCODING`s, (constant) `SYMBOL`s in the “CHARSET” package, `STRING`s (denoting `iconv`-based encodings), the symbol `:DEFAULT`, and the line terminator keywords `:UNIX`, `:MAC`, `:DOS`. The default encoding is `CUSTOM:*DEFAULT-FILE-ENCODING*`. This argument determines how the lisp `CHARACTER` data is converted to/from the 8-bit bytes that the underlying OS uses.

  See also Section 21.7, “Function `STREAM-EXTERNAL-FORMAT`”.

`:BUFFERED`

  `NIL`, `T`, or `:DEFAULT`. Have CLISP manage an internal buffer for input or output (in addition to the buffering that might be used by the underlying OS). Buffering is a known general technique to significantly speed up i/o.

  - for functions that create `SOCKET:SOCKET-STREAM`s and pipes, `:DEFAULT` is equivalent to `T` on the input side and to `NIL` on the output side; if you are transmitting a lot of data then using buffering will significantly speed up your i/o;
  - for functions that open files, `:DEFAULT` means that buffered file streams will be returned for regular files and (on UNIX) block-devices, and unbuffered file streams for special files.

  Note that some files, notably those on the `/proc` filesystem (on UNIX systems), are actually, despite their innocuous appearance, special files, so you might need to supply an explicit `:BUFFERED` `NIL` argument for them. Actually, CLISP detects that the file is a `/proc` file, so that one is covered, but there are probably more strange beasts out there!

### Variable `CUSTOM:*REOPEN-OPEN-FILE*`

When an already opened file is opened again, and not both the existing and the new `STREAM`s are read-only (i.e., `:DIRECTION` is `:INPUT` or `:INPUT-IMMUTABLE`), the streams can mess up each other and produce unexpected results. The user variable `CUSTOM:*REOPEN-OPEN-FILE*` controls how CLISP handles the situation and can take 4 values:

`NIL`
  do nothing: do not even check that there are other `STREAM`s pointing to the same file
`WARN`
  `SIGNAL` a `WARNING` and proceed
`CLOSE`
  `CLOSE` the other `STREAM`s and proceed (this could be dangerous and is not generally recommended)
`ERROR` (default)
  `SIGNAL` a continuable `ERROR`

## 21.13. Function `CLEAR-INPUT`

Calling `CLEAR-INPUT` on a `STREAM` removes the `end-of-stream` state, thus making it available for further input.

This allows reading from a file as it is being appended to, as if with tail -f.

## 21.14. Function `CLOSE`

Function `CLOSE` is a `GENERIC-FUNCTION`, see Chapter 30, Gray streams.

When the `:ABORT` argument is non-`NIL`, `CLOSE` will not `SIGNAL`s an `ERROR` even when the underlying OS call fails.

`GET-OUTPUT-STREAM-STRING` returns the same value after `CLOSE` as it would before it.

`CLOSE` on an already closed `STREAM` does nothing and returns `T`.

If you do not `CLOSE` your `STREAM` explicitly, it will be closed at garbage-collection time automatically (with `(`CLOSE` `stream` `:ABORT` `T`)`). This is not recommended though because garbage-collection is not deterministic. Please use `WITH-OPEN-STREAM` etc.

## 21.15. Function `OPEN-STREAM-P`

Function `OPEN-STREAM-P` is a `GENERIC-FUNCTION`, see Chapter 30, Gray streams.

## 21.16. Class `BROADCAST-STREAM`

`INPUT-STREAM-P` and `INTERACTIVE-STREAM-P` return false for `BROADCAST-STREAM`s.

## 21.17. Functions `EXT:MAKE-BUFFERED-INPUT-STREAM` and `EXT:MAKE-BUFFERED-OUTPUT-STREAM`

`(EXT:MAKE-BUFFERED-OUTPUT-STREAM `function`)`. Returns a buffered output `STREAM`. `function` is a `FUNCTION` expecting one argument, a `SIMPLE-STRING`. `WRITE-CHAR` collects the `CHARACTER`s in a `STRING`, until a newline character is written or `FORCE-OUTPUT`/`FINISH-OUTPUT` is called. Then `function` is called with a `SIMPLE-STRING` as argument, that contains the characters collected so far. `CLEAR-OUTPUT` discards the characters collected so far.

`(EXT:MAKE-BUFFERED-INPUT-STREAM `function` `mode`)`. Returns a buffered input `STREAM`. `function` is a `FUNCTION` of 0 arguments that returns either `NIL` (stands for `end-of-stream`) or up to three values `string`, `start`, `end`. `READ-CHAR` returns the `CHARACTER`s of the current `string` one after another, as delimited by `start` and `end`, which default to `0` and `NIL`, respectively. When the `string` is consumed, `function` is called again. The `string` returned by `function` should not be changed by the user. `function` should copy the `string` with `COPY-SEQ` or `SUBSEQ` before returning if the original `string` is to be modified. `mode` determines the behavior of `LISTEN` when the current `string` buffer is empty:

`NIL`
  the stream acts like a `FILE-STREAM`, i.e. `function` is called
`T`
  the stream acts like an interactive stream without `end-of-stream`, i.e. one can assume that further characters will always arrive, without calling `function`
`FUNCTION`
  this `FUNCTION` tells, upon call, if further non-empty `string`s are to be expected.

`CLEAR-INPUT` discards the rest of the current `string`, so `function` will be called upon the next `READ-CHAR` operation.

## 21.18. Function `EXT:STREAM-HANDLES`

The function `(EXT:STREAM-HANDLES `stream`)` returns two values:

1. The OS file descriptor for the input side of the `stream`, or `NIL` if the `stream` is an output-only `STREAM` or if there is no file descriptor associated with it.
2. The OS file descriptor for the output side of the `stream`, or `NIL` if the `stream` is an input-only `STREAM` or if there is no file descriptor associated with it.

### Warning

It is dangerous to `CLOSE` the file descriptors returned by this function. This may lead to `EBADF` OS `ERROR`s and, eventually, segmentation faults. Always use `CLOSE` on the original Lisp `stream`s instead.

## Chapter 22. Printer [chap-22]

## 22.1. Multiple Possible Textual Representations [sec_22-1-1-1]

### Variable `CUSTOM:*PRINT-CLOSURE*`

An additional variable `CUSTOM:*PRINT-CLOSURE*` controls whether compiled and interpreted functions (closures) are output in detailed form. If `CUSTOM:*PRINT-CLOSURE*` is non-`NIL`, a readable syntax is used for closures:

interpreted closures
  `#S`(`FUNCTION` ...)
compiled closures
  `#Y(...)` (this is what you would see if you open a CLISP `#P".fas"` in a text editor)

This feature is turned off by `WITH-STANDARD-IO-SYNTAX` because it is easy to get wrong (see below) and non-portable.

### Warning

Closures often refer to value cells or other entities from the lexical environment. The correct operation of a `FUNCTION` may depend on the access to the same value cells as some other, related `FUNCTION`s. If you want to `WRITE` and `READ` back `FUNCTION`s so that their semantics is preserved, you have to `WRITE` and `READ` all `FUNCTION`s that share some structure in the lexical environment together, and you have to either bind `*PRINT-READABLY*` to `T` or use `WITH-STANDARD-IO-SYNTAX`:

    (SETF (VALUES my-pop my-push)
          `(LET ((storage ()))
             (VALUES (LAMBDA () (POP storage))
                     (LAMBDA (x) (PUSH x storage)))))
    (LET ((pair (READ-FROM-STRING
                 (WITH-STANDARD-IO-SYNTAX
                   (LET ((CUSTOM:*PRINT-CLOSURE* T))
                     (PRIN1-TO-STRING (CONS my-pop my-push)))))))
       (SETQ my-pop-1 (CAR pair)
             my-push-1 (CDR pair)))

Note that `my-pop` and `my-push` share environment between themselves but not with `my-pop-1` and `my-push-1` which can be easily seen if you do

    (LET ((CUSTOM:*PRINT-CLOSURE* T) (*PRINT-CIRCLE* T))
      (PRINT (LIST my-pop my-push my-pop-1 my-push-1)))

but which is not at all obvious from the usual `#<` output.

`CUSTOM:*PRINT-CLOSURE*` is initially set to `NIL`.

### Variable `CUSTOM:*PRINT-RPARS*`

An additional variable `CUSTOM:*PRINT-RPARS*` controls the output of the right (closing) parentheses. If `CUSTOM:*PRINT-RPARS*` is non-`NIL`, closing parentheses which do not fit onto the same line as the the corresponding opening parenthesis are output just below their corresponding opening parenthesis, in the same column.

`CUSTOM:*PRINT-RPARS*` is initially set to `NIL`.

### Variable `CUSTOM:*PRINT-INDENT-LISTS*`

An additional variable `CUSTOM:*PRINT-INDENT-LISTS*` controls the indentation of lists that span more than one line. It specifies by how many characters items within the list will be indented relative to the beginning of the list.

`CUSTOM:*PRINT-INDENT-LISTS*` is initially set to `1`.

### Variable `CUSTOM:*PPRINT-FIRST-NEWLINE*`

An additional variable `CUSTOM:*PPRINT-FIRST-NEWLINE*` controls pretty-printing of multi-line objects. When `CUSTOM:*PPRINT-FIRST-NEWLINE*` is non-`NIL`, and the current line already has some characters on it, and the next object will be printed on several lines, and it does not start with a #\Newline, then a #\Newline is printed before the object. E.g., when you type `(`FORMAT` `T` "return value: ~S~%" `v`)` you want want to see a terse one-line output when `v` is something short (like `0` or `NIL` or `T`), but you probably want to see something nice, like

    return value:
    (long list which does not fit
     on one line)

instead of

    return value: (long list which does not fit
     on one line)

when it does not.

`CUSTOM:*PPRINT-FIRST-NEWLINE*` has no effect if `*PRINT-PRETTY*` is `NIL`.

`CUSTOM:*PPRINT-FIRST-NEWLINE*` is initially set to `T`.

## 22.2. Printing Floats [sec_22-1-3-1-3]

In the absence of `SYS::WRITE-FLOAT-DECIMAL`, floating point numbers are output in radix 2. This function is defined in `floatprint.lisp` and is not available if you run CLISP without a memory image (which you should never do anyway!)

If `*PRINT-READABLY*` is true, `*READ-DEFAULT-FLOAT-FORMAT*` has no influence on the way `FLOAT`s are printed.

## 22.3. Printing Characters [sec_22-1-3-2]

Characters are printed as specified in [ANSI CL standard] using `#\`, with one exception: when printer escaping is in effect, the space character is printed as “`#\Space`” when the variable `CUSTOM:*PRINT-SPACE-CHAR-ANSI*` is `NIL`. When `CUSTOM:*PRINT-SPACE-CHAR-ANSI*` is non-`NIL`, it is printed as “`#\` ”; this is how [ANSI CL standard] specifies it.

## 22.4. Package Prefixes for Symbols [sec_22-1-3-3-1]

Variable `CUSTOM:*PRINT-SYMBOL-PACKAGE-PREFIX-SHORTEST*`. When `CUSTOM:*PRINT-SYMBOL-PACKAGE-PREFIX-SHORTEST*` is non-`NIL`, the package prefix is not the `PACKAGE-NAME` but the shortest (nick)name as returned by `EXT:PACKAGE-SHORTEST-NAME`. This variable is ignored when `*PRINT-READABLY*` is non-`NIL`.

## 22.5. Printing Other Vectors [sec_22-1-3-7]

When `*PRINT-READABLY*` is true, other vectors are written as follows: if the `ARRAY-ELEMENT-TYPE` is `T`, the syntax `#(`x1` ... `xn`)` is used. Otherwise, the syntax `#A(`element-type` `dimensions` `contents`)` is used.

## 22.6. Printing Other Arrays [sec_22-1-3-8]

When `*PRINT-READABLY*` is true, other arrays are written as follows: if the `ARRAY-ELEMENT-TYPE` is `T`, the syntax ``#`rank`A` `contents`` is used. Otherwise, the syntax `#A(`element-type` `dimensions` `contents`)` is used.

As explicitly permitted by this section, specialized `BIT` and `CHARACTER` `ARRAY`s are printed with the innermost lists generated by the printing algorithm being instead printed using `BIT-VECTOR` and `STRING` syntax, respectively.

Variable `CUSTOM:*PRINT-EMPTY-ARRAYS-ANSI*`. Empty `ARRAY`s, i.e., arrays with no elements and zero `ARRAY-TOTAL-SIZE` (because one of its dimensions is zero) are printed with the readable syntax `#A(`element-type` `dimensions` `contents`)`, unless the variable `CUSTOM:*PRINT-EMPTY-ARRAYS-ANSI*` is non-`NIL`, in which case the arrays are printed using the [ANSI CL standard]-prescribed syntax ``#`rank`A` `contents`` which often loses the dimension information.

### 22.6.1. Printing Pathnames [sec_22-1-3-11]

Pathnames are printed as follows: If `*PRINT-ESCAPE*` is `NIL`, only the namestring is printed; otherwise it is printed with the `#P` syntax, as per the [ANSI CL standard] issue PRINT-READABLY-BEHAVIOR:CLARIFY. But, if `*PRINT-READABLY*` is true, we are in trouble as `#P` is ambiguous (which is verboten when `*PRINT-READABLY*` is true), while being mandated by the [ANSI CL standard]. Therefore, in this case, CLISP's behavior is determined by the value of `CUSTOM:*PRINT-PATHNAMES-ANSI*`: when it is `NIL`, we print pathnames like this: ``#-`CLISP `#P`"..." `#+`CLISP `#S`(`PATHNAME` ...)`. Otherwise, when the variable `CUSTOM:*PRINT-PATHNAMES-ANSI*` is non-`NIL`, the `#P` notation is used as per [sec_1-5-1-4-1] “Resolution of Apparent Conflicts in Exceptional Situations”.

### Note

The `#S` notation for `PATHNAME`s is used extensively in the [Common Lisp HyperSpec] (see examples for `PATHNAME`, `PATHNAMEP`, `PARSE-NAMESTRING` et al), but was decided against, see PATHNAME-PRINT-READ:SHARPSIGN-P.

### Warning

When both `*PRINT-READABLY*` and `CUSTOM:*PRINT-PATHNAMES-ANSI*` are non-`NIL` and the namestring will be parsed to a dissimilar object (with the current value of `CUSTOM:*PARSE-NAMESTRING-DOT-FILE*`), an `ERROR` of type `PRINT-NOT-READABLE` is `SIGNAL`ed.

## 22.7. The Lisp Pretty Printer [sec_22-2]

The Lisp Pretty Printer implementation is not perfect yet. `PPRINT-LOGICAL-BLOCK` does not respect `*PRINT-LINES*`.

### 22.7.1. Pretty Print Dispatch Table [sec_22-2-1-4]

A pprint dispatch table is a `CONS` of a `SYMBOL` `*PRINT-PPRINT-DISPATCH*` and an association list which maps types into priorities and print functions. Their use is strongly discouraged because of the performance issues: when `*PRINT-PPRINT-DISPATCH*` is non-trivial and `*PRINT-PRETTY*` is non-`NIL`, printing of every object requires a lookup in the table, which entails many calls to `TYPEP` (which cannot be made fast enough).

## 22.8. Formatted Output [sec_22-3]

### Function `FORMAT`

The additional `FORMAT` instruction `~!` is similar to `~/`, but avoids putting a function name into a string, thus it is `READ` in the current `*PACKAGE*`, so, even if the function is not interned in the “COMMON-LISP-USER” package, you might not need to specify the package explicitly. `(`FORMAT` `stream` "~arguments!" `function` `object`)` is equivalent to `(`FUNCALL` `function` `stream` `object` `colon-modifier-p` `atsign-modifier-p` `arguments`)`.

The additional `FORMAT` instruction `~.` is a kind of opposite to `~&`: It outputs a conditional newline, by calling the function `EXT:ELASTIC-NEWLINE`. `~`n`.` outputs `n-1` newlines followed by an `EXT:ELASTIC-NEWLINE`. `~0.` does nothing.

`FORMAT` `~R` and `FORMAT` `~:R` can output only integers in the range `|`n`| < `1066``. The output is in English, according to the American conventions, and these conventions are identical to the British conventions only in the range `|`n`| < `109``.

`FORMAT` `~:@C` does not output the character itself, only the instruction how to type the character.

For `FORMAT` `~E` and `FORMAT` `~G`, the value of `*READ-DEFAULT-FLOAT-FORMAT*` does not matter if `*PRINT-READABLY*` is true.

`FORMAT` `~T` can determine the current column of any built-in stream.

## 22.9. Functions `WRITE` & `WRITE-TO-STRING`

The functions `WRITE` and `WRITE-TO-STRING` have an additional keyword argument `:CLOSURE` which is used to bind `CUSTOM:*PRINT-CLOSURE*`.

## 22.10. Macro `PRINT-UNREADABLE-OBJECT`

Variable `CUSTOM:*PRINT-UNREADABLE-ANSI*`. The macro `PRINT-UNREADABLE-OBJECT`, when invoked without body forms, suppresses the trailing space if only the type is to be printed, and suppresses the leading space if only the identity is to be printed. This behaviour can be turned off set setting the variable `CUSTOM:*PRINT-UNREADABLE-ANSI*` to a non-`NIL` value: in this case, a trailing or leading space are output, as prescribed by [ANSI CL standard].

## 22.11. Miscellaneous Issues

`*PRINT-CASE*` controls the output not only of symbols, but also of characters and some `#<unreadable>` objects.

Platform Dependent: UNIX, Win32 platforms only.
  `*PRINT-PRETTY*` is initially `NIL` but set to `T` in `config.lisp`. This makes screen output prettier.

`*PRINT-ARRAY*` is initially set to `T`.

## Chapter 23. Reader [chap-23]

## 23.1. Effect of Readtable Case on the Lisp Reader [sec_23-1-2]

When the value of `(`READTABLE-CASE` `readtable`)` is `:INVERT`, it applies to the package name and the symbol name of a symbol separately (not to the entire token at once). An alternative to the use of `READTABLE-CASE` is the use of the `:CASE-SENSITIVE` option of `MAKE-PACKAGE` and `DEFPACKAGE`.

## 23.2. The `recursive-p` argument [sec_23-1-3-2]

When non-`NIL` `recursive-p` argument is passed to a top-level `READ` call, an `ERROR` is `SIGNAL`ed.

## Chapter 24. System Construction [chap-24]

The compiler can be called not only by the functions `COMPILE`, `COMPILE-FILE` and `DISASSEMBLE`, but also by the declaration `(COMPILE)`.

## 24.1. Function `COMPILE-FILE`

`COMPILE-FILE` compiles a file to a platform-independent bytecode:

    (COMPILE-FILE filename &KEY :OUTPUT-FILE :LISTING :EXTERNAL-FORMAT
                                ((:WARNINGS CUSTOM:*COMPILE-WARNINGS*) CUSTOM:*COMPILE-WARNINGS*)
                                ((:VERBOSE *COMPILE-VERBOSE*) *COMPILE-VERBOSE*)
                                ((:PRINT *COMPILE-PRINT*) *COMPILE-PRINT*))

Options for `COMPILE-FILE`

`filename`
  the file to be compiled, should be a pathname designator.
`:OUTPUT-FILE`
  should be `NIL` or `T` or a pathname designator or an output `STREAM`. The default is `T`.
`:LISTING`
  should be `NIL` or `T` or a pathname designator or an output `STREAM`. The default is `NIL`.
`:EXTERNAL-FORMAT`
  the `EXT:ENCODING` of the `filename`.
`:WARNINGS`
  specifies whether warnings should also appear on the screen.
`:VERBOSE`
  specifies whether error messages should also appear on the screen.
`:PRINT`
  specifies whether an indication which forms are being compiled should appear on the screen.

The variables `CUSTOM:*COMPILE-WARNINGS*` (initially set to `T`), `*COMPILE-VERBOSE*` (initially set to `T`, affected by `-v`) `*COMPILE-PRINT*` (initially set to `NIL`, affected by `-v`) provide defaults for the `:WARNINGS`, `:VERBOSE`, `:PRINT` keyword arguments, respectively, and are bound by `COMPILE-FILE` to the values of the arguments, i.e., these arguments are recursive.

### 24.1.1. Output files

For each input file (default file type: `#P".lisp"`) the following files are generated:

File | When | Default file type | Contents
--- | --- | --- | ---
output file | only if `:OUTPUT-FILE` is not `NIL` | `#P".fas"` | can be loaded using the `LOAD` function
auxiliary output file | only if `:OUTPUT-FILE` is not `NIL` | `#P".lib"` | used by `COMPILE-FILE` when compiling a `REQUIRE` form referring to the input file
listing file | only if `:LISTING` is not `NIL` | `#P".lis"` | disassembly of the output file
C output file | only if `:OUTPUT-FILE` is not `NIL` | `#P".c"` | “FFI”; this file is created only if the source contains “FFI” forms

### Warning

If you have two files in the same directory - `#P"foo.lisp"` and `#P"foo.c"`, and you compile the first file with CLISP, the second file will be clobbered if you have any “FFI” forms in the first one!

### 24.1.2. Return values

As per [ANSI CL standard], `COMPILE-FILE` returns 3 values:

output-truename
  the truename of the output `#P".fas"`, or `NIL` if the file could not be created, in which case the compilation is considered to have failed
warnings-p
  `NIL` if no conditions of type `ERROR` or `WARNING` were detected during compilation, and the number of such conditions otherwise
failure-p
  `NIL` if no conditions of type `ERROR` or `WARNING` (other than `STYLE-WARNING`) were detected during compilation, and the number of such conditions otherwise

Since CLISP tends to be relatively garrulous with warnings (see, e.g., Section 12.2.4.1, “Rule of Float Precision Contagion sec_12-1-4-4”), the non-`NIL` tertiary return value (called `failure-p` by the [ANSI CL standard]) does not indicate a failure of compilation. The correct way to check whether `COMPILE-FILE` has failed is the primary return value.

## 24.2. Function `COMPILE-FILE-PATHNAME`

The default for the `:OUTPUT-FILE` argument is `T`, which means `#P".fas"`.

## 24.3. Function `REQUIRE`

The function `REQUIRE` receives as the optional argument either a `PATHNAME` or a `LIST` of `PATHNAME`s: files to be `LOAD`ed if the required module is not already present.

### 24.3.1. Return value

When the module is already present, `NIL` is returned; otherwise returns the `TRUENAME` which was loaded to satisfy the `REQUIRE`ment (or `LIST` thereof iff the second argument is a `LIST`).

### 24.3.2. Additional `LOAD` locations

In addition to (and before) `CUSTOM:*LOAD-PATHS*`, `REQUIRE` tries to find the file to `LOAD` in the following locations:

- Platform Dependent: Only in CLISP built without configure flag `--without-dynamic-modules`.

  The system-wide external modules directory `(`MERGE-PATHNAMES` "dynmod/" `CUSTOM:*LIB-DIRECTORY*`)`.

- Platform Dependent: Only in CLISP built without configure flag `--without-dynamic-modules`.

  The user external modules directory `(`MERGE-PATHNAMES` "dynmod/" `CUSTOM:*USER-LIB-DIRECTORY*`)` (when `CUSTOM:*USER-LIB-DIRECTORY*` is non-`NIL`).

- When `REQUIRE` was called while `LOAD`ing, the directory with the file being loaded (i.e., `(`MAKE-PATHNAME` :name `NIL` :type `NIL` :defaults `*LOAD-TRUENAME*`)`).

### 24.3.3. User variable `CUSTOM::*MODULE-PROVIDER-FUNCTIONS*`

When `REQUIRE` is called without the second (pathname) argument, the elements of the `CUSTOM::*MODULE-PROVIDER-FUNCTIONS*` `LIST` are called one by one on the first (module name) argument until one of them returns non-`NIL`. If all of them return `NIL`, `LOAD` is called as described above.

Initially the lisp is empty; `(require "`asdf`")` modifies it (Platform Dependent: if CLISP was configured with the option `--with-module=asdf`).

### 24.3.4. Interaction with `COMPILE-FILE`

At compile time, `(`REQUIRE` `#P"foo"`)` forms are treated specially: `CUSTOM:*LOAD-PATHS*` is searched for `#P"foo.lisp"` and `#P"foo.lib"`. If the latest such file is a `#P".lisp"`, it is compiled; otherwise the `#P".lib"` is loaded. If neither is found, `(`REQUIRE` `#P"foo"`)` is called.

### Warning

It is a very bad idea to name your files the same way as CLISP modules (whether system-supplied or user-installed) because then `REQUIRE` will use different files at compile and execution times.

The `#P".lib"` is a “header” file which contains the constant, variable, inline and macro definitions necessary for compilation of the files that `REQUIRE` this file, but not the function definitions and calls that are not necessary for that. Thus it is not necessary to either enclose `REQUIRE` forms in `EVAL-WHEN` or to load the required files in the makefiles: if you have two files, `#P"foo.lisp"` and `#P"bar.lisp"`, and the latter requires the former, you can write in your `Makefile`:

    all: foo.fas bar.fas

    foo.fas: foo.lisp
    	clisp -c foo

    bar.fas: bar.lisp foo.fas
    	clisp -c bar

instead of the more cumbersome (and slower, since `#P".lib"`s are usually smaller and load faster that `#P".fas"`s):

    bar.fas: bar.lisp foo.fas
            clisp -i foo -c bar

Thus, you do not need to `(`LOAD` `#P"foo"`)` in order to `(`COMPILE-FILE` `#P"bar.lisp"`)`. If memory is tight, and if `#P"foo.lisp"` contains only a few inline functions, macros, constants or variables, this is a space and time saver. If `#P"foo.lisp"` does a lot of initializations or side effects when being loaded, this is important as well.

## 24.4. Function `LOAD`

`LOAD` accepts four additional keyword arguments `:ECHO`, `:COMPILING`, `:EXTRA-FILE-TYPES`, and `:OBSOLETE-ACTION`.

    (LOAD filename &KEY ((:VERBOSE *LOAD-VERBOSE*) *LOAD-VERBOSE*)
                        ((:PRINT *LOAD-PRINT*) *LOAD-PRINT*)
                        ((:ECHO CUSTOM:*LOAD-ECHO*) CUSTOM:*LOAD-ECHO*) :IF-DOES-NOT-EXIST
                        ((:COMPILING CUSTOM:*LOAD-COMPILING*) CUSTOM:*LOAD-COMPILING*) :EXTRA-FILE-TYPES
                        ((:OBSOLETE-ACTION CUSTOM:*LOAD-OBSOLETE-ACTION*) CUSTOM:*LOAD-OBSOLETE-ACTION*)
                        (ignore-pathname-defaults nil))

`:VERBOSE`
  causes `LOAD` to emit a short message that a file is being loaded. The default is `*LOAD-VERBOSE*`, which is initially `T`, but can be changed by the `-v` option.
`:PRINT`
  causes `LOAD` to print the value of each form. The default is `*LOAD-PRINT*`, which is initially `NIL`, but can be changed by the `-v` option.
`:ECHO`
  causes the input from the file to be echoed to `*STANDARD-OUTPUT*` (normally to the screen). Should there be an error in the file, you can see at one glance where it is. The default is `CUSTOM:*LOAD-ECHO*` , which is initially `NIL`, but can be changed by the `-v` option.
`:COMPILING`
  causes each form read to be compiled on the fly. The compiled code is executed at once and - in contrast to `COMPILE-FILE` - not written to a file. The default is `CUSTOM:*LOAD-COMPILING*` , which is initially `NIL`, but can be changed by the `-C` option.
`:EXTRA-FILE-TYPES`

  Specifies the `LIST` of additional file types considered for loading, in addition to `CUSTOM:*SOURCE-FILE-TYPES*` (which is initially `("lisp" "lsp" "cl")`) and `CUSTOM:*COMPILED-FILE-TYPES*` (which is initially `("fas")`).

  When `filename` does not specify a unique file (e.g., `filename` is `#P"foo"` and both `#P"foo.lisp"` and `#P"foo.fas"` are found in the `CUSTOM:*LOAD-PATHS*`), then the newest file is loaded.

`:OBSOLETE-ACTION`

  Specifies the action to take when loading a `#P".fas"` with a different bytecode version from the one supported by this CLISP version. The possible actions are

  `:DELETE`
    delete the `#P".fas"` and proceed as with `NIL`
  `:ERROR`
    `SIGNAL` an `ERROR`
  `:COMPILE`
    recompile the source file (if found in `CUSTOM:*LOAD-PATHS*`) and `LOAD` the result
  `NIL` (default)
    `WARN` and look for another matching file

  If no file can be loaded and `:IF-DOES-NOT-EXIST` is non-`NIL`, an `ERROR` is `SIGNAL`ed. The default is `CUSTOM:*LOAD-OBSOLETE-ACTION*` , which is initially `NIL`.

`:IGNORE-PATHNAME-DEFAULTS`
  Do not merge `*DEFAULT-PATHNAME-DEFAULTS*` to the argument using `MERGE-PATHNAMES` (as required by [ANSI CL standard]) and rely on `CUSTOM:*LOAD-PATHS*` instead.

The variables `*LOAD-VERBOSE*`, `*LOAD-PRINT*`, `CUSTOM:*LOAD-OBSOLETE-ACTION*`, `CUSTOM:*LOAD-COMPILING*`, and `CUSTOM:*LOAD-ECHO*` are bound by `LOAD` when it receives a corresponding keyword argument (`:VERBOSE`, `:PRINT`, `:OBSOLETE-ACTION`, `:COMPILING`, and `:ECHO`), i.e., these arguments are recursive, just like the arguments `:WARNINGS`, `:VERBOSE`, and `:PRINT` for `COMPILE-FILE`.

When evaluation of a read form `SIGNAL`s an `ERROR`, three `RESTART`s are available:

`SKIP`
  Skip this form and read the next one.
`RETRY`
  Try to evaluate this form again.
`STOP`
  Stop loading the file.

On success, `LOAD` returns the `TRUENAME` of the file which it loaded, or the `filename` argument if it is a `STREAM` but not a `FILE-STREAM`.

Variable `CUSTOM:*LOAD-PATHS*`. The variable `CUSTOM:*LOAD-PATHS*` contains a list of directories where the files are looked for - in addition to the specified or current directory - by `LOAD`, `REQUIRE`, `COMPILE-FILE` and `LOAD-LOGICAL-PATHNAME-TRANSLATIONS`.

## 24.5. Variable `*FEATURES*`

The variable `*FEATURES*` initially contains the following symbols

Default `*FEATURES*`

`:CLISP`
  the name of this implementation
`:ANSI-CL`
  CLISP purports to conform to [ANSI CL standard]
`:COMMON-LISP`
  required by [ANSI CL standard]
`:INTERPRETER`
  `EVAL` is implemented
`:COMPILER`
  `COMPILE` and `COMPILE-FILE` are implemented
`:SOCKETS`
  see Section 32.4, “Socket Streams”
`:MT`
  see Section 32.5, “Multiple Threads of Execution”
`:GENERIC-STREAMS`
  see Section 31.6, “Generic streams”
`:LOGICAL-PATHNAMES`
  Logical Pathnames are implemented
`:FFI`
  if a foreign function interface (see Section 32.3, “The Foreign Function Call Facility”) is supported (Platform Dependent: Many UNIX, Win32 platforms only)
`:GETTEXT`
  if internationalization (see Section 31.4, “Internationalization of CLISP”) using the GNU gettext package is supported (Platform Dependent: most UNIX platforms only)
`:UNICODE`
  if UNICODE (ISO 10646) characters are supported (see Section 31.5, “Encodings”)
`:LOOP`
  “extended” `LOOP` form is implemented
`:CLOS`
  CLOS is implemented
`:MOP`
  Meta-Object Protocol is implemented
`:WORD-SIZE=64`
  if CLISP was built for a 64-bit CPU. This could be useful on platforms with 64-bit CPUs which have a 32-bit mode emulation (e.g., i386 is emulated on x86_64 and ia64) so that the user can decide which ABI library to load dynamically using “FFI”.
`:WIN32`
  if `hardware` = PC (clone) and `operating system` = Win32 (Windows 95/98/Me/NT/2000/XP)
`:PC386`
  if `hardware` = PC (clone). It can be used as an indicator for the mainstream hardware characteristics (such as the existence of a graphics card with a non-graphics text mode, or the presence of a keyboard with arrows and Insert/Delete keys, or an ISA/VLB/PCI bus) or software characteristics (such as the Control+Alternate+Delete keyboard combination).
`:UNIX`
  if `operating system` = UNIX (in this case the `hardware` is irrelevant!)
`:BEOS`
  if `operating system` = BeOS (in that case `:UNIX` is also present)
`:HAIKU`
  if `operating system` = Haiku (in that case `:UNIX` is also present)
`:CYGWIN`
  if CLISP is using the Cygwin UNIX compatibility layer on top of Win32 (in that case `:UNIX` is also present)
`:MACOS`
  if `operating system` = Mac OS X (in that case `:UNIX` is also present)

Each module should add the appropriate keyword, e.g., `:SYSCALLS`, `:DIRKEY`, `:REGEXP`, `:PCRE`, etc.

## 24.6. Function `EXT:FEATUREP` [CLRFI-1]

`(EXT:FEATUREP `form`)` provides run-time access to the read-time conditionals `#+` and `#-`. `form` is a feature exression.

## 24.7. Function `EXT:COMPILED-FILE-P` [CLRFI-2]

`(`EXT:COMPILED-FILE-P` `filename`)` returns non-`NIL` when the file `filename` exists, is readable, and appears to be a CLISP-compiled `#P".fas"` file compatible with the currently used bytecode format.

System definition facilities (such as `asdf` or `defsystem`) can use it to determine whether the file needs to be recompiled.

## Chapter 25. Environment [chap-25]

## 25.1. Top Level Loop [sec_25-1-1]

The debugger may be invoked through the functions `INVOKE-DEBUGGER`, `BREAK`, `SIGNAL`, `ERROR`, `CERROR`, `WARN`. The stepper is invoked through the macro `STEP`. Debugger and stepper execute subordinate read-eval-print loop (called break loops) which are similar to the main read-eval-print loop except for the prompt and the set of available commands. Commands must be typed literally, in any case, without surrounding quotes or whitespace. Each command has a keyword abbreviation, indicated in the second column.

Table 25.1. Commands common to the main loop, the debugger and the stepper

command | abbreviation | operation
--- | --- | ---
help | :h | print a list of available commands
LocalSymbols | :ls | print the list of `SYMBOL`s `INTERN`ed in a given `PACKAGE`.

Table 25.2. Commands common to the debugger and the stepper

command | abbreviation | operation
--- | --- | ---
Abort | :a | abort to the next most recent read-eval-print loop
Unwind | :uw | abort to the next most recent read-eval-print loop
Quit | :q | quit to the top read-eval-print loop

The stack is organized into frames and other stack elements. Usually every invocation of an interpreted function and every evaluation of an interpreted form corresponds to one stack frame. Special forms such as `LET`, `LET*`, `UNWIND-PROTECT` and `CATCH` produce special kinds of stack frames.

In a break loop there is a current stack frame, which is initially the most recent stack frame but can be moved using the debugger commands Up and Down.

Evaluation of forms in a break loop occurs in the lexical environment of the current stack frame and at the same time in the dynamic environment of the debugger's caller. This means that to inspect or modify a lexical variable all you have to do is to move the current stack frame to be just below the frame that corresponds to the form or the function call that binds that variable.

Stack Printing Mode. There is a current stack mode which defines in how much detail the stack is shown by the stack-related debugger commands (backtrace et al):

1. All the stack elements are considered. This mode works fine for debugging compiled functions.
2. All the frames are considered.
3. Only lexical frames (frames that correspond to special forms that modify the lexical environment) are considered.
4. Only `EVAL` and `APPLY` frames are considered. Every evaluation of a form in the interpreter corresponds to an `EVAL` frame. This is the default.
5. Only `APPLY` frames are considered. Every invocation of an interpreted function corresponds to one `APPLY` frame.

Table 25.3. Commands common to the debugger and the stepper

command | abbreviation | operation
--- | --- | ---
Error | :e | print the last error object.
Inspect | :i | `INSPECT` the last error object.
Where | :w | show the current stack frame.
Up | :u | go up one frame, i.e., to the caller if in mode-5
Down | :d | do down one frame, i.e., to the callee if in mode-5
Top | :t | go to top frame, i.e., to the top-level form if in mode-4
Bottom | :b | go to bottom (most recent) frame, i.e., most probably to the form or function that caused the debugger to be entered.
Mode `stack-mode` | :m `stack-mode` | set the current stack printing mode
Frame-limit `l` | :fl | set the `frame-limit`: this many frames will be printed by backtrace at most.
backtrace [`stack-mode` [`l`]] | :bt [`stack-mode` [`l`]] | list the stack in the given `stack-mode`, bottom frame first, top frame last; at most `l` frames are printed; calls `EXT:SHOW-STACK`.

If the current stack frame is an `EVAL` or `APPLY` frame, the following commands are available as well:

Table 25.4. Commands specific to `EVAL`/`APPLY`

command | abbreviation | operation
--- | --- | ---
Break+ | :br+ | set a breakpoint in the current frame. When the corresponding form or function will be left, the debugger will be entered again, with the variable `EXT:*TRACE-VALUES*` containing a list of its values.
Break- | :br- | remove a breakpoint from the current frame.
Redo | :rd | re-evaluate the corresponding form or function call. This command can be used to restart parts of a computation without aborting it entirely.
Return `value` | :rt `value` | leave the current frame, returning the given value.

Table 25.5. Commands specific to the debugger

command | abbreviation | operation
--- | --- | ---
Continue | :c | continue evaluation of the program.

Table 25.6. Commands specific to the stepper

command | abbreviation | operation
--- | --- | ---
Step | :s | step into a form: evaluate this form in single step mode
Next | :n | step over a form: evaluate this form at once
Over | :o | step over this level: evaluate at once up to the next return
Continue | :c | switch off single step mode, continue evaluation

The stepper is usually used like this: If some form returns a strange value or results in an error, call `(`STEP` `form`)` and navigate using the commands Step and Next until you reach the form you regard as responsible. If you are too fast (execute Next once and get the error), there is no way back; you have to restart the entire stepper session. If you are too slow (stepped into a function or a form which certainly is OK), a couple of Next commands or one Over command will help.

### 25.1.1. User-defined Commands

You can set `CUSTOM:*USER-COMMANDS*` to a list of `FUNCTION`s, each returning a `LIST` of bindings, i.e., either a

`STRING`
  the help string printed by help in addition to the standard CLISP help
`CONS` `(`STRING` . `FUNCTION`)`
  the actual binding: when the user types the string, the function is called on the remainder of the string, i.e., the part of the string after the command.

E.g.,

    (setq CUSTOM:*USER-COMMANDS*
          (list (lambda () (list (format nil "~2%User-defined commands:")))
                (lambda ()
                  (flet ((panic (argline)
                           (format t "don't panic~@[ because of ~A~], ~D~%"
                                   (and (plusp (length argline)) argline)
                                   (random 42))))
                    (list (format nil "~%panic   :p    hit the panic button!")
                          (cons "panic" #'panic)
                          (cons ":p" #'panic))))
                (lambda ()
                  (let ((curses #("ouch" "yuk" "bletch")))
                    (flet ((swear (argline)
                             (format t "~A: ~A!~%" argline
                                     (aref curses (random (length curses))))))
                      (list (format nil "~%swear   :e    curse")
                            (cons "swear" #'swear)
                            (cons ":e" #'swear)))))))

## 25.2. Debugging Utilities [sec_25-1-2]

List of Examples

25.1. Identifying Individual Calls in `TRACE`

### 25.2.1. Function `DISASSEMBLE`

Platform Dependent: UNIX platform only.
  `DISASSEMBLE` can disassemble to machine code, provided that GNU gdb is present. In that case the argument may be a `EXT:SYSTEM-FUNCTION`, a `FFI:FOREIGN-FUNCTION`, a special operator handler, a `SYMBOL` denoting one of these, an `INTEGER` (address), or a `STRING`.

### 25.2.2. Function `EXT:UNCOMPILE`

The function `EXT:UNCOMPILE` does the converse of `COMPILE`: `(`EXT:UNCOMPILE` `function`)` reverts a compiled `function` (name), that has been entered or loaded in the same session and then compiled, back to its interpreted form.

### 25.2.3. Function `EXT:SHOW-STACK`

The function `EXT:SHOW-STACK` is called by the backtrace command.

It prints to `*STANDARD-OUTPUT*` and accepts 3 optional arguments:

1. `stack-mode`
2. `frame-limit`
3. `start-frame`

It can used to find out what all the threads are up to:

    (LOOP :with out = *STANDARD-OUTPUT* :for thread :in (MT:LIST-THREADS) :do
       (FORMAT out "===~A===~;" thread)
       (MT:THREAD-INTERRUPT thread :function
         (LAMBDA () (LET ((*STANDARD-OUTPUT* out)) (EXT:SHOW-STACK 1 3)))))

### 25.2.4. Function `DOCUMENTATION`

No on-line documentation is available for the system functions (yet), but see Section 25.2.5, “Function `DESCRIBE`”.

### 25.2.5. Function `DESCRIBE`

When `CUSTOM:*BROWSER*` is non-`NIL`, and `CUSTOM:CLHS-ROOT` returns a valid URL, `DESCRIBE` on a standard Common Lisp symbol will point your web browser to the appropriate [Common Lisp HyperSpec] page.

Also, when `CUSTOM:*BROWSER*` is non-`NIL`, and `CUSTOM:IMPNOTES-ROOT` returns a valid URL, `DESCRIBE` on symbols and packages documented in these implementation notes will point your web browser to the appropriate page.

To do this, `DESCRIBE` will retrieve the appropriate tables from `CUSTOM:CLHS-ROOT` and `CUSTOM:IMPNOTES-ROOT` on the first relevant invocation. These operations are logged to `CUSTOM:*HTTP-LOG-STREAM*`.

Function `CUSTOM:CLHS-ROOT`. Function `CUSTOM:CLHS-ROOT` is defined in `config.lisp`. By default it looks at `(`EXT:GETENV` "CLHSROOT")` and `CUSTOM:*CLHS-ROOT-DEFAULT*`, but you may redefine it in `config.lisp` or RC file. The return value should be a `STRING` terminated with a `"/"`, e.g., http://www.ai.mit.edu/projects/iiip/doc/CommonLISP/HyperSpec/ or `/usr/doc/HyperSpec/`. If the return value is `NIL`, the feature is completely disabled. `CUSTOM:*CLHS-ROOT-DEFAULT*` is initialized in `config.lisp` based on the `--hyperspec` passed to the top-level configure script when CLISP was built.

Function `CUSTOM:IMPNOTES-ROOT`. Function `CUSTOM:IMPNOTES-ROOT` is defined in `config.lisp`. By default it looks at `(`EXT:GETENV` "IMPNOTES")` and `CUSTOM:*IMPNOTES-ROOT-DEFAULT*`, but you may redefine it in `config.lisp` or RC file. The return value should be a `STRING` terminated with a `"/"`, e.g., http://clisp.org/impnotes/, or the path to the monolithic page, e.g., http://clisp.org/impnotes.html or `/usr/doc/clisp/impnotes.html`. If the return value is `NIL`, the feature is completely disabled.

### 25.2.6. Macro `TRACE`

List of Examples

25.1. Identifying Individual Calls in `TRACE`

`(`TRACE` `function-name` ...)` makes the functions `function-name`, ... traced. Each `function-name` should be either a function name or a `LIST` `(`function-name` `&KEY` `:SUPPRESS-IF` `:MAX-DEPTH` `:STEP-IF` `:BINDINGS` `:PRE` `:POST` `:PRE-BREAK-IF` `:POST-BREAK-IF` `:PRE-PRINT` `:POST-PRINT` `:PRINT`)`, where

`:SUPPRESS-IF` `form`
  no trace output as long as `form` is true
`:MAX-DEPTH` `form`
  no trace output as long as `(> *trace-level* `form`)`. This is useful for tracing functions that are use by the tracer itself, such as `PRINT-OBJECT`, or otherwise when tracing would lead to an infinite recursion.
`:STEP-IF` `form`
  invokes the stepper as soon as `form` is true
`:BINDINGS` ((`variable` `form`)...)
  binds `variable`s to the result of evaluation of `form`s around evaluation of all of the following forms
`:PRE` `form`
  evaluates `form` before calling the function
`:POST` `form`
  evaluates `form` after return from the function
`:PRE-BREAK-IF` `form`
  goes into the break loop before calling the function if `form` is true
`:POST-BREAK-IF` `form`
  goes into the break loop after return from the function if `form` is true
`:PRE-PRINT` `form`
  prints the values of `form` before calling the function
`:POST-PRINT` `form`
  prints the values of `form` after return from the function
`:PRINT` `form`
  prints the values of `form` both before calling and after return from the function

In all these forms you can access the following variables:

`EXT:*TRACE-FUNCTION*`
  the traced function itself
`EXT:*TRACE-ARGS*`
  the arguments to the function
`EXT:*TRACE-FORM*`
  the function/macro call as form
`EXT:*TRACE-VALUES*`
  after return from the function: the list of return values from the function call

and you can leave the function call with specified values by using `RETURN`.

`TRACE` and `UNTRACE` are also applicable to functions `(`SETF` `symbol`)` and to macros, but not to locally defined functions and macros.

#### Trace output

`TRACE` prints this line before evaluating the form: ``trace level`. Trace: `form`` and after evaluating the form it prints: ``trace level`. Trace: `function-name` ==> `result`` where “trace level” is the total nesting level.

#### Variable `CUSTOM:*TRACE-INDENT*`

If you want the `TRACE` level to be indicated by the indentation in addition to the printed numbers, set `CUSTOM:*TRACE-INDENT*` to non-`NIL`. Initially it is `NIL` since many nested traced calls will easily exhaust the available line length.

#### Examples

Example 25.1. Identifying Individual Calls in `TRACE`

Suppose the trace level above is not enough for you to identify individual calls. You can give each call a unique id and print it:

    (defun f0 (x)
      (cond ((zerop x) 1)
            ((zerop (random 2)) (* x (f0 (1- x))))
            (t (* x (f1 (1- x))))))
    ⇒ F0
    (defun f1 (x)
      (cond ((zerop x) 1)
            ((zerop (random 2)) (* x (f0 (1- x))))
            (t (* x (f1 (1- x))))))
    ⇒ F1
    (defvar *f0-call-count* 0)
    ⇒ *F0-CALL-COUNT*
    (defvar *id0*)
    ⇒ *ID0*
    (defvar *cc0*)
    ⇒ *CC0*
    (defvar *f1-call-count* 0)
    ⇒ *F1-CALL-COUNT*
    (defvar *id1*)
    ⇒ *ID1*
    (defvar *cc1*)
    ⇒ *CC1*
    (trace (f0 :bindings ((*cc0* (incf *f0-call-count*))
                          (*id0* (gensym "F0-")))
               :pre-print (list 'enter *id0* *cc0*)
               :post-print (list 'exit *id0* *cc0*))
           (f1 :bindings ((*cc1* (incf *f1-call-count*))
                          (*id1* (gensym "F1-")))
               :pre-print (list 'enter *id1* *cc1*)
               :post-print (list 'exit *id1* *cc1*)))
    ;; Tracing function F0.
    ;; Tracing function F1.
    ⇒ (F0 F1)
    (f0 10)
    1. Trace: (F0 '10)
    (ENTER #:F0-2926 1)
    2. Trace: (F1 '9)
    (ENTER #:F1-2927 1)
    3. Trace: (F0 '8)
    (ENTER #:F0-2928 2)
    4. Trace: (F1 '7)
    (ENTER #:F1-2929 2)
    5. Trace: (F1 '6)
    (ENTER #:F1-2930 3)
    6. Trace: (F1 '5)
    (ENTER #:F1-2931 4)
    7. Trace: (F1 '4)
    (ENTER #:F1-2932 5)
    8. Trace: (F0 '3)
    (ENTER #:F0-2933 3)
    9. Trace: (F1 '2)
    (ENTER #:F1-2934 6)
    10. Trace: (F0 '1)
    (ENTER #:F0-2935 4)
    11. Trace: (F1 '0)
    (ENTER #:F1-2936 7)
    (EXIT #:F1-2936 7)
    11. Trace: F1 ==> 1
    (EXIT #:F0-2935 4)
    10. Trace: F0 ==> 1
    (EXIT #:F1-2934 6)
    9. Trace: F1 ==> 2
    (EXIT #:F0-2933 3)
    8. Trace: F0 ==> 6
    (EXIT #:F1-2932 5)
    7. Trace: F1 ==> 24
    (EXIT #:F1-2931 4)
    6. Trace: F1 ==> 120
    (EXIT #:F1-2930 3)
    5. Trace: F1 ==> 720
    (EXIT #:F1-2929 2)
    4. Trace: F1 ==> 5040
    (EXIT #:F0-2928 2)
    3. Trace: F0 ==> 40320
    (EXIT #:F1-2927 1)
    2. Trace: F1 ==> 362880
    (EXIT #:F0-2926 1)
    1. Trace: F0 ==> 3628800
    ⇒ 3628800
    *f0-call-count*
    ⇒ 4
    *f1-call-count*
    ⇒ 7

### 25.2.7. Function `INSPECT`

The function `INSPECT` accepts a keyword argument `:FRONTEND`, which specifies the way CLISP will interact with the user, and defaults to `CUSTOM:*INSPECT-FRONTEND*`.

Available `:FRONTEND`s for `INSPECT` in CLISP

`:TTY`
  The interaction is conducted via the `*TERMINAL-IO*` stream. Please use the help command to get the list of all available commands.
`:HTTP`

  A window in your Web browser (specified by the `:BROWSER` keyword argument) is opened and it is controlled by CLISP via a `SOCKET:SOCKET-STREAM`, using the HTTP protocol. You should be able to use all the standard browser features.

  Since CLISP is not multitasking at this time, you will not be able to do anything else during an `INSPECT` session. Please click on the `quit` link to terminate the session.

  Please be aware though, that once you terminate an `INSPECT` session, all links in all `INSPECT` windows in your browser will become obsolete and using them in a new `INSPECT` session will result in unpredictable behavior.

The function `INSPECT` also accepts a keyword argument `:BROWSER`, which specifies the browser used by the `:HTTP` front-end and defaults to `CUSTOM:*INSPECT-BROWSER*`.

The function `INSPECT` binds some pretty-printer variables:

Variable | Bound to
--- | ---
`*PRINT-LENGTH*` | `CUSTOM:*INSPECT-PRINT-LENGTH*`
`*PRINT-LEVEL*` | `CUSTOM:*INSPECT-PRINT-LEVEL*`
`*PRINT-LINES*` | `CUSTOM:*INSPECT-PRINT-LINES*`

User variable `CUSTOM:*INSPECT-LENGTH*` specifies the number of sequence elements or slots printed in detail when a sequence or a structure or a CLOS object is inspected.

### 25.2.8. Macro `TIME`

The timing data printed by the macro `TIME` includes:

- the real time (“wall” time, `GET-INTERNAL-REAL-TIME`),
- the run time (processor time for this process, `GET-INTERNAL-RUN-TIME`),
- the number of bytes allocated, and
- the number of garbage-collections performed, if any.

The macro `EXT:TIMES` (mnemonic: “TIME and Space”) is like the macro `TIME`: `(`EXT:TIMES` `form`)` evaluates the `form`, and, as a side effect, outputs detailed information about the memory allocations caused by this evaluation. It also prints everything printed by `TIME`.

### 25.2.9. Function `ED`

The function `ED` calls the external editor specified by the value of `(`EXT:GETENV` "EDITOR")` or, failing that, the value of the variable `CUSTOM:*EDITOR*` (set in `config.lisp`). If the argument is a function name which was defined in the current session (not loaded from a file), the program text to be edited is a pretty-printed version (without comments) of the text which was used to define the function.

### 25.2.10. Functions `APROPOS` & `APROPOS-LIST`

The search performed by `APROPOS` and `APROPOS-LIST` is case-insensitive.

Variable `CUSTOM:*APROPOS-DO-MORE*`. You can make `APROPOS` print more information about the symbols it found by setting `CUSTOM:*APROPOS-DO-MORE*` to a list containing some of `:FUNCTION`, `:VARIABLE`, `:TYPE`, and `:CLASS` or just set it to `T` to get all of the values.

Variable `CUSTOM:*APROPOS-MATCHER*`. You can make `APROPOS` and `APROPOS-LIST` be more flexible in their search by setting `CUSTOM:*APROPOS-MATCHER*` to a `FUNCTION` of one argument, a pattern (a `STRING`), returning a new `FUNCTION` of one argument, a `SYMBOL` name (also a `STRING`), which returns non-`NIL` when the symbol name matches the pattern for the purposes of `APROPOS`. When `CUSTOM:*APROPOS-MATCHER*` is `NIL`, `SEARCH` is used. Some modules come with functions which can be used for `CUSTOM:*APROPOS-MATCHER*`, e.g., `REGEXP:REGEXP-MATCHER`, `POSIX:FNMATCH-MATCHER`, `PCRE:PCRE-MATCHER`.

### 25.2.11. Function `DRIBBLE`

If `DRIBBLE` is called with an argument, and dribbling is already enabled, a warning is printed, and the new dribbling request is ignored.

Dribbling is implemented via a kind (but not a recognizable subtype) of `TWO-WAY-STREAM`, named `EXT:DRIBBLE-STREAM`. If you have a `source` bidirectional `STREAM` `x` and you want all transactions (input and output) on `x` to be copied to the `target` output `STREAM` `y`, you can do

    (DEFVAR *loggable* x)
    (SETQ x (MAKE-SYNONYM-STREAM '*loggable*))
    (DEFUN toggle-logging (&OPTIONAL s)
      (MULTIPLE-VALUE-BIND (source target) (dribble-toggle *loggable* s)
        (WHEN (STREAMP source) (SETQ *loggable* source))
        target))
    (toggle-logging y)	; start logging
    ...
    (toggle-logging)	; finish logging
    ...
    (toggle-logging y)	; restart logging
    ...
    (toggle-logging)	; finish logging
    (CLOSE y)

`(`EXT:DRIBBLE-STREAM` `stream`)`
  When `stream` is a `EXT:DRIBBLE-STREAM`, returns two values: the `source` and the `target` streams. Otherwise returns `NIL`.
`(`EXT:DRIBBLE-STREAM-P` `stream`)`
  When `stream` is a `EXT:DRIBBLE-STREAM`, returns `T`, otherwise returns `NIL`.
`(`EXT:DRIBBLE-STREAM-SOURCE` `stream`)`
  When `stream` is a `EXT:DRIBBLE-STREAM`, returns its `source` stream, otherwise signals a `TYPE-ERROR`.
`(`EXT:DRIBBLE-STREAM-TARGET` `stream`)`
  When `stream` is a `EXT:DRIBBLE-STREAM`, returns its `target` stream, otherwise signals a `TYPE-ERROR`.
`(`EXT:MAKE-DRIBBLE-STREAM` `source` `target`)`
  Create a new `EXT:DRIBBLE-STREAM`.
`(`EXT:DRIBBLE-TOGGLE` `stream` `&OPTIONAL` `pathname`)`
  When `stream` is a `EXT:DRIBBLE-STREAM` and `pathname` is `NIL`, writes a dribble termination note to the `stream`'s `target` `STREAM` and returns `stream`'s `source` and `target` `STREAM`s; when `stream` is not a `EXT:DRIBBLE-STREAM` and `pathname` is non-`NIL`, creates a new `EXT:DRIBBLE-STREAM`, dribbling from `stream` to `pathname`, writes a dribble initialization note to `pathname`, and return the `EXT:DRIBBLE-STREAM` (the second value is the `target` `STREAM`); otherwise `WARN` that no appropriate action may be taken. `pathname` may be an open output `STREAM` or a pathname designator. See above for the sample usage. See also `src/dribble.lisp` in the CLISP source tree.

#### 25.2.11.1. Scripting and `DRIBBLE`

`DRIBBLE` works by operating on `*TERMINAL-IO*`, thus is does not work when CLISP acts as a script interpreter (see Section 32.6.2, “Scripting with CLISP”).

Traditionally, Common Lisp implementations set `*STANDARD-INPUT*`, `*STANDARD-OUTPUT*`, and `*ERROR-OUTPUT*` to a `SYNONYM-STREAM` pointing to `*TERMINAL-IO*`, and CLISP is no exception. Thus changing `*TERMINAL-IO*` to a dribble stream affects all standard i/o.

On the other hand, when CLISP acts as a script interpreter, it adheres to the UNIX <`stdio.h`> conventions, thus `*STANDARD-INPUT*`, `*STANDARD-OUTPUT*`, and `*ERROR-OUTPUT*` are normal `FILE-STREAM`s, and thus are not affected by `DRIBBLE` (`*TERMINAL-IO*` - and thus `(`PRINT` ... `T`)` - is still affected). The [ANSI CL standard] explicitly permits this behavior by stating

> `DRIBBLE` is intended primarily for interactive debugging; its effect cannot be relied upon when used in a program.

## 25.3. Environment Inquiry [sec_25-1-3]

### 25.3.1. Function `ROOM`

The function `ROOM` returns five values:

1. space occupied by Lisp objects (in bytes)
2. space available for allocating Lisp objects until the next garbage-collection is triggered (in bytes)
3. space permanently allocated (in bytes)
4. the number of times garbage-collection was done in this CLISP session
5. the cumulative space freed by all the garbage-collections in this CLISP session (in bytes)
6. the total time (in `INTERNAL-TIME-UNITS-PER-SECOND`) spent collecting garbage

### 25.3.2. Function `EXT:GC`

This function starts a global garbage-collection and returns the same values as `ROOM`.

When the optional parameter is non-`NIL` also invalidates just-in-time compiled objects.

### 25.3.3. Machine

Platform Dependent: UNIX platform only.
  The functions `SHORT-SITE-NAME`, `LONG-SITE-NAME` should be defined in a site-specific `config.lisp` file. The default implementations try to read the value of the environment variable `ORGANIZATION`, and, failing that, call `uname`.
Platform Dependent: Win32 platform only.
  The functions `SHORT-SITE-NAME`, `LONG-SITE-NAME` should be defined in a site-specific `config.lisp` file. The default implementations try to read the registry.

### 25.3.4. Function `LISP-IMPLEMENTATION-VERSION`

`LISP-IMPLEMENTATION-VERSION` returns the numeric version (like `3.14`), and the release date (like `"1999-07-21"`). When running on the same machine on which CLISP was built, it appends the binary build and memory image dump date in universal time (like `3141592654`). When running on a different machine, it appends the `MACHINE-INSTANCE` of the machine on which it was built.

### 25.3.5. Function `EXT:ARGV`

This function will return a fresh `SIMPLE-VECTOR` of `STRING` command line arguments passed to the runtime, including those already processed by CLISP. Use `EXT:*ARGS*` instead of this function to get the arguments for your program.

## 25.4. Time [sec_25-1-4]

Default Time Zone

Platform Dependent: No platform supports this currently
  The variable `CUSTOM:*DEFAULT-TIME-ZONE*` contains the default time zone used by `ENCODE-UNIVERSAL-TIME` and `DECODE-UNIVERSAL-TIME`. It is initially set to -1 (which means 1 hour east of Greenwich, i.e., Mid European Time).

The time zone in a decoded time does not necessarily have be an `INTEGER`, but (as `FLOAT` or `RATIONAL` number) it should be a multiple of `1/3600`.

Table 25.7. Time granularity

platform | UNIX | Win32
--- | --- | ---
`INTERNAL-TIME-UNITS-PER-SECOND` | 1,000,000 | 10,000,000

`GET-INTERNAL-RUN-TIME` returns the amount of run time consumed by the current CLISP process since its startup.

## Chapter 26. Glossary [chap-26]

No notes.

## Chapter 27. Appendix [chap-a]

No notes.

## Chapter 28. X3J13 Issue Index [CLHS-ic]

This is the list of [ANSI CL standard] issues and their current status in CLISP, i.e., whether CLISP supports code that makes use of the functionality specified by the vote.

X3J13 Issues

&ENVIRONMENT-BINDING-ORDER:FIRST
  yes
ACCESS-ERROR-NAME
  yes
ADJUST-ARRAY-DISPLACEMENT
  yes
ADJUST-ARRAY-FILL-POINTER
  yes
ADJUST-ARRAY-NOT-ADJUSTABLE:IMPLICIT-COPY
  yes
ALLOCATE-INSTANCE:ADD
  yes
ALLOW-LOCAL-INLINE:INLINE-NOTINLINE
  yes
ALLOW-OTHER-KEYS-NIL:PERMIT
  yes
AREF-1D
  yes
ARGUMENT-MISMATCH-ERROR-AGAIN:CONSISTENT
  yes
ARGUMENT-MISMATCH-ERROR-MOON:FIX
  yes
ARGUMENT-MISMATCH-ERROR:MORE-CLARIFICATIONS
  yes, except for argument list checking in `CALL-NEXT-METHOD` in compiled code (items 11,12)
ARGUMENTS-UNDERSPECIFIED:SPECIFY
  yes
ARRAY-DIMENSION-LIMIT-IMPLICATIONS:ALL-FIXNUM
  yes
ARRAY-TYPE-ELEMENT-TYPE-SEMANTICS:UNIFY-UPGRADING
  yes
ASSERT-ERROR-TYPE:ERROR
  yes
ASSOC-RASSOC-IF-KEY
  yes
ASSOC-RASSOC-IF-KEY:YES
  yes
BOA-AUX-INITIALIZATION:ERROR-ON-READ
  yes
BREAK-ON-WARNINGS-OBSOLETE:REMOVE
  yes
BROADCAST-STREAM-RETURN-VALUES:CLARIFY-MINIMALLY
  yes
BUTLAST-NEGATIVE:SHOULD-SIGNAL
  yes
CHANGE-CLASS-INITARGS:PERMIT
  yes
CHAR-NAME-CASE:X3J13-MAR-91
  yes
CHARACTER-LOOSE-ENDS:FIX
  yes
CHARACTER-PROPOSAL:2
  yes
CHARACTER-PROPOSAL:2-1-1
  yes
CHARACTER-PROPOSAL:2-1-2
  yes
CHARACTER-PROPOSAL:2-2-1
  yes
CHARACTER-PROPOSAL:2-3-1
  yes
CHARACTER-PROPOSAL:2-3-2
  yes
CHARACTER-PROPOSAL:2-3-3
  yes
CHARACTER-PROPOSAL:2-3-4
  yes
CHARACTER-PROPOSAL:2-3-5
  yes
CHARACTER-PROPOSAL:2-3-6
  yes
CHARACTER-PROPOSAL:2-4-1
  yes
CHARACTER-PROPOSAL:2-4-2
  yes
CHARACTER-PROPOSAL:2-4-3
  yes
CHARACTER-PROPOSAL:2-5-2
  yes
CHARACTER-PROPOSAL:2-5-6
  yes
CHARACTER-PROPOSAL:2-5-7
  yes
CHARACTER-PROPOSAL:2-6-1
  yes
CHARACTER-PROPOSAL:2-6-2
  yes
CHARACTER-PROPOSAL:2-6-3
  yes
CHARACTER-PROPOSAL:2-6-5
  yes
CHARACTER-VS-CHAR:LESS-INCONSISTENT-SHORT
  yes
CLASS-OBJECT-SPECIALIZER:AFFIRM
  yes
CLOS-CONDITIONS-AGAIN:ALLOW-SUBSET
  yes
CLOS-CONDITIONS:INTEGRATE
  yes
CLOS-ERROR-CHECKING-ORDER:NO-APPLICABLE-METHOD-FIRST
  yes
CLOS-MACRO-COMPILATION:MINIMAL
  yes
CLOSE-CONSTRUCTED-STREAM:ARGUMENT-STREAM-ONLY
  yes
CLOSED-STREAM-OPERATIONS:ALLOW-INQUIRY
  yes
COERCING-SETF-NAME-TO-FUNCTION:ALL-FUNCTION-NAMES
  yes
COLON-NUMBER
  yes
COMMON-FEATURES:SPECIFY
  yes
COMMON-TYPE:REMOVE
  yes
COMPILE-ARGUMENT-PROBLEMS-AGAIN:FIX
  yes
COMPILE-FILE-HANDLING-OF-TOP-LEVEL-FORMS:CLARIFY
  yes
COMPILE-FILE-OUTPUT-FILE-DEFAULTS:INPUT-FILE
  yes
COMPILE-FILE-PACKAGE
  yes
COMPILE-FILE-PATHNAME-ARGUMENTS:MAKE-CONSISTENT
  yes
COMPILE-FILE-SYMBOL-HANDLING:NEW-REQUIRE-CONSISTENCY
  yes
COMPILED-FUNCTION-REQUIREMENTS:TIGHTEN
  yes
COMPILER-DIAGNOSTICS:USE-HANDLER
  yes
COMPILER-LET-CONFUSION:ELIMINATE
  yes
COMPILER-VERBOSITY:LIKE-LOAD
  yes
COMPILER-WARNING-STREAM
  yes
COMPLEX-ATAN-BRANCH-CUT:TWEAK
  yes
COMPLEX-ATANH-BOGUS-FORMULA:TWEAK-MORE
  yes
COMPLEX-RATIONAL-RESULT:EXTEND
  yes
COMPUTE-APPLICABLE-METHODS:GENERIC
  yes
CONCATENATE-SEQUENCE:SIGNAL-ERROR
  yes
CONDITION-ACCESSORS-SETFABLE:NO
  yes
CONDITION-RESTARTS:BUGGY
  yes
CONDITION-RESTARTS:PERMIT-ASSOCIATION
  yes
CONDITION-SLOTS:HIDDEN
  yes
CONS-TYPE-SPECIFIER:ADD
  yes
CONSTANT-CIRCULAR-COMPILATION:YES
  yes
CONSTANT-COLLAPSING:GENERALIZE
  yes
CONSTANT-COMPILABLE-TYPES:SPECIFY
  yes
CONSTANT-FUNCTION-COMPILATION:NO
  CLISP can dump compiled functions defined in the global lexical environment. Interpreted functions can not be dumped; this should not be a problem, because an interpreted function in a compiled file usually indicate a programmer error (often an extra `QUOTE`).
CONSTANT-MODIFICATION:DISALLOW
  yes
CONSTANTP-DEFINITION:INTENTIONAL
  yes
CONSTANTP-ENVIRONMENT:ADD-ARG
  yes
CONTAGION-ON-NUMERICAL-COMPARISONS:TRANSITIVE
  yes
COPY-SYMBOL-COPY-PLIST:COPY-LIST
  yes
COPY-SYMBOL-PRINT-NAME:EQUAL
  yes
DATA-IO:ADD-SUPPORT
  yes
DATA-TYPES-HIERARCHY-UNDERSPECIFIED
  yes
DEBUGGER-HOOK-VS-BREAK:CLARIFY
  yes
DECLARATION-SCOPE:NO-HOISTING
  yes
DECLARE-ARRAY-TYPE-ELEMENT-REFERENCES:RESTRICTIVE
  yes
DECLARE-FUNCTION-AMBIGUITY:DELETE-FTYPE-ABBREVIATION
  yes
DECLARE-MACROS:FLUSH
  yes
DECLARE-TYPE-FREE:LEXICAL
  yes
DECLS-AND-DOC
  there is no writeup, but all affected operators are fully implemented as specified
DECODE-UNIVERSAL-TIME-DAYLIGHT:LIKE-ENCODE
  yes
DEFCONSTANT-SPECIAL:NO
  yes
DEFGENERIC-DECLARE:ALLOW-MULTIPLE
  yes
DEFINE-COMPILER-MACRO:X3J13-NOV89
  yes
DEFINE-CONDITION-SYNTAX:INCOMPATIBLY-MORE-LIKE-DEFCLASS+EMPHASIZE-READ-ONLY
  yes
DEFINE-METHOD-COMBINATION-BEHAVIOR:CLARIFY
  no
DEFINING-MACROS-NON-TOP-LEVEL:ALLOW
  yes
DEFMACRO-BLOCK-SCOPE:EXCLUDES-BINDINGS
  yes
DEFMACRO-LAMBDA-LIST:TIGHTEN-DESCRIPTION
  yes
DEFMETHOD-DECLARATION-SCOPE:CORRESPONDS-TO-BINDINGS
  yes
DEFPACKAGE:ADDITION
  yes
DEFSTRUCT-CONSTRUCTOR-KEY-MIXTURE:ALLOW-KEY
  yes
DEFSTRUCT-CONSTRUCTOR-OPTIONS:EXPLICIT
  yes
DEFSTRUCT-CONSTRUCTOR-SLOT-VARIABLES:NOT-BOUND
  yes
DEFSTRUCT-COPIER-ARGUMENT-TYPE:RESTRICT
  yes
DEFSTRUCT-COPIER:ARGUMENT-TYPE
  yes
DEFSTRUCT-DEFAULT-VALUE-EVALUATION:IFF-NEEDED
  yes
DEFSTRUCT-INCLUDE-DEFTYPE:EXPLICITLY-UNDEFINED
  yes
DEFSTRUCT-PRINT-FUNCTION-AGAIN:X3J13-MAR-93
  yes
DEFSTRUCT-PRINT-FUNCTION-INHERITANCE:YES
  yes
DEFSTRUCT-REDEFINITION:ERROR
  yes
DEFSTRUCT-SLOTS-CONSTRAINTS-NAME:DUPLICATES-ERROR
  yes
DEFSTRUCT-SLOTS-CONSTRAINTS-NUMBER
  yes
DEFTYPE-DESTRUCTURING:YES
  yes
DEFTYPE-KEY:ALLOW
  yes
DEFVAR-DOCUMENTATION:UNEVALUATED
  yes
DEFVAR-INIT-TIME:NOT-DELAYED
  yes
DEFVAR-INITIALIZATION:CONSERVATIVE
  yes
DEPRECATION-POSITION:LIMITED
  yes
DESCRIBE-INTERACTIVE:NO
  yes
DESCRIBE-UNDERSPECIFIED:DESCRIBE-OBJECT
  yes
DESTRUCTIVE-OPERATIONS:SPECIFY
  yes
DESTRUCTURING-BIND:NEW-MACRO
  yes
DISASSEMBLE-SIDE-EFFECT:DO-NOT-INSTALL
  yes
DISPLACED-ARRAY-PREDICATE:ADD
  yes
DO-SYMBOLS-BLOCK-SCOPE:ENTIRE-FORM
  yes
DO-SYMBOLS-DUPLICATES
  yes
DOCUMENTATION-FUNCTION-BUGS:FIX
  yes
DOCUMENTATION-FUNCTION-TANGLED:REQUIRE-ARGUMENT
  yes
DOTIMES-IGNORE:X3J13-MAR91
  yes
DOTTED-LIST-ARGUMENTS:CLARIFY
  yes
DOTTED-MACRO-FORMS:ALLOW
  yes
DRIBBLE-TECHNIQUE
  yes
DYNAMIC-EXTENT-FUNCTION:EXTEND
  yes
DYNAMIC-EXTENT:NEW-DECLARATION
  yes
EQUAL-STRUCTURE:MAYBE-STATUS-QUO
  yes
ERROR-TERMINOLOGY-WARNING:MIGHT
  yes
EVAL-OTHER:SELF-EVALUATE
  yes
EVAL-TOP-LEVEL:LOAD-LIKE-COMPILE-FILE
  yes
EVAL-WHEN-NON-TOP-LEVEL:GENERALIZE-EVAL-NEW-KEYWORDS
  yes
EVAL-WHEN-OBSOLETE-KEYWORDS:X3J13-MAR-1993
  no
EVALHOOK-STEP-CONFUSION:FIX
  yes
EVALHOOK-STEP-CONFUSION:X3J13-NOV-89
  yes
EXIT-EXTENT-AND-CONDITION-SYSTEM:LIKE-DYNAMIC-BINDINGS
  yes
EXIT-EXTENT:MINIMAL
  yes, actually implement MEDIUM
EXPT-RATIO:P.211
  yes
EXTENSIONS-POSITION:DOCUMENTATION
  yes
EXTERNAL-FORMAT-FOR-EVERY-FILE-CONNECTION:MINIMUM
  yes
EXTRA-RETURN-VALUES:NO
  yes
FILE-OPEN-ERROR:SIGNAL-FILE-ERROR
  yes
FIXNUM-NON-PORTABLE:TIGHTEN-DEFINITION
  yes
FLET-DECLARATIONS
  yes
FLET-DECLARATIONS:ALLOW
  yes
FLET-IMPLICIT-BLOCK:YES
  yes
FLOAT-UNDERFLOW:ADD-VARIABLES
  yes
FLOATING-POINT-CONDITION-NAMES:X3J13-NOV-89
  yes
FORMAT-ATSIGN-COLON
  yes
FORMAT-COLON-UPARROW-SCOPE
  yes
FORMAT-COMMA-INTERVAL
  yes
FORMAT-E-EXPONENT-SIGN:FORCE-SIGN
  yes
FORMAT-OP-C
  yes
FORMAT-PRETTY-PRINT:YES
  yes, except that `~F`, `~E`, `~G`, `~$` also bind `*PRINT-BASE*` to 10 and `*PRINT-RADIX*` to `NIL`
FORMAT-STRING-ARGUMENTS:SPECIFY
  yes
FUNCTION-CALL-EVALUATION-ORDER:MORE-UNSPECIFIED
  yes
FUNCTION-COMPOSITION:JAN89-X3J13
  yes
FUNCTION-DEFINITION:JAN89-X3J13
  yes
FUNCTION-NAME:LARGE
  yes
FUNCTION-TYPE
  yes
FUNCTION-TYPE-ARGUMENT-TYPE-SEMANTICS:RESTRICTIVE
  yes
FUNCTION-TYPE-KEY-NAME:SPECIFY-KEYWORD
  yes
FUNCTION-TYPE-REST-LIST-ELEMENT:USE-ACTUAL-ARGUMENT-TYPE
  yes
FUNCTION-TYPE:X3J13-MARCH-88
  yes
GENERALIZE-PRETTY-PRINTER:UNIFY
  no
GENERIC-FLET-POORLY-DESIGNED:DELETE
  yes
GENSYM-NAME-STICKINESS:LIKE-TEFLON
  yes
GENTEMP-BAD-IDEA:DEPRECATE
  yes
GET-MACRO-CHARACTER-READTABLE:NIL-STANDARD
  yes
GET-SETF-METHOD-ENVIRONMENT:ADD-ARG
  yes
HASH-TABLE-ACCESS:X3J13-MAR-89
  yes
HASH-TABLE-KEY-MODIFICATION:SPECIFY
  yes
HASH-TABLE-PACKAGE-GENERATORS:ADD-WITH-WRAPPER
  yes
HASH-TABLE-REHASH-SIZE-INTEGER
  yes
HASH-TABLE-SIZE:INTENDED-ENTRIES
  yes
HASH-TABLE-TESTS:ADD-EQUALP
  yes
IEEE-ATAN-BRANCH-CUT:SPLIT
  yes
IGNORE-USE-TERMINOLOGY:VALUE-ONLY
  yes
IMPORT-SETF-SYMBOL-PACKAGE
  yes
IN-PACKAGE-FUNCTIONALITY:MAR89-X3J13
  yes
IN-SYNTAX:MINIMAL
  yes
INITIALIZATION-FUNCTION-KEYWORD-CHECKING
  yes
ISO-COMPATIBILITY:ADD-SUBSTRATE
  yes
JUN90-TRIVIAL-ISSUES:11
  yes
JUN90-TRIVIAL-ISSUES:14
  yes
JUN90-TRIVIAL-ISSUES:24
  yes
JUN90-TRIVIAL-ISSUES:25
  yes
JUN90-TRIVIAL-ISSUES:27
  yes for `THE`, no for `APPLY` (spec not clear)
JUN90-TRIVIAL-ISSUES:3
  yes
JUN90-TRIVIAL-ISSUES:4
  yes
JUN90-TRIVIAL-ISSUES:5
  yes
JUN90-TRIVIAL-ISSUES:9
  yes
KEYWORD-ARGUMENT-NAME-PACKAGE:ANY
  yes
LAST-N
  yes
LCM-NO-ARGUMENTS:1
  yes
LEXICAL-CONSTRUCT-GLOBAL-DEFINITION:UNDEFINED
  yes
LISP-PACKAGE-NAME:COMMON-LISP
  yes
LISP-SYMBOL-REDEFINITION-AGAIN:MORE-FIXES
  yes
LISP-SYMBOL-REDEFINITION:MAR89-X3J13
  yes
LOAD-OBJECTS:MAKE-LOAD-FORM
  yes
LOAD-TIME-EVAL:R**2-NEW-SPECIAL-FORM
  obsolete
LOAD-TIME-EVAL:R**3-NEW-SPECIAL-FORM
  yes
LOAD-TRUENAME:NEW-PATHNAME-VARIABLES
  yes
LOCALLY-TOP-LEVEL:SPECIAL-FORM
  yes
LOOP-AND-DISCREPANCY:NO-REITERATION
  yes
LOOP-FOR-AS-ON-TYPO:FIX-TYPO
  yes
LOOP-INITFORM-ENVIRONMENT:PARTIAL-INTERLEAVING-VAGUE
  no
LOOP-MISCELLANEOUS-REPAIRS:FIX
  yes
LOOP-NAMED-BLOCK-NIL:OVERRIDE
  yes
LOOP-PRESENT-SYMBOLS-TYPO:FLUSH-WRONG-WORDS
  yes
LOOP-SYNTAX-OVERHAUL:REPAIR
  yes
MACRO-AS-FUNCTION:DISALLOW
  yes
MACRO-DECLARATIONS:MAKE-EXPLICIT
  yes
MACRO-ENVIRONMENT-EXTENT:DYNAMIC
  yes
MACRO-FUNCTION-ENVIRONMENT
  obsolete
MACRO-FUNCTION-ENVIRONMENT:YES
  yes
MACRO-SUBFORMS-TOP-LEVEL-P:ADD-CONSTRAINTS
  no
MACROEXPAND-HOOK-DEFAULT:EXPLICITLY-VAGUE
  yes
MACROEXPAND-HOOK-INITIAL-VALUE:IMPLEMENTATION-DEPENDENT
  yes
MACROEXPAND-RETURN-VALUE:TRUE
  yes
MAKE-LOAD-FORM-CONFUSION:REWRITE
  yes
MAKE-LOAD-FORM-SAVING-SLOTS:NO-INITFORMS
  yes
MAKE-PACKAGE-USE-DEFAULT:IMPLEMENTATION-DEPENDENT
  yes
MAP-INTO:ADD-FUNCTION
  yes
MAPPING-DESTRUCTIVE-INTERACTION:EXPLICITLY-VAGUE
  yes
METACLASS-OF-SYSTEM-CLASS:UNSPECIFIED
  yes
METHOD-COMBINATION-ARGUMENTS:CLARIFY
  no
METHOD-INITFORM:FORBID-CALL-NEXT-METHOD
  no
MUFFLE-WARNING-CONDITION-ARGUMENT
  yes
MULTIPLE-VALUE-SETQ-ORDER:LIKE-SETF-OF-VALUES
  yes
MULTIPLE-VALUES-LIMIT-ON-VARIABLES:UNDEFINED
  yes
NINTERSECTION-DESTRUCTION
  yes
NINTERSECTION-DESTRUCTION:REVERT
  yes
NOT-AND-NULL-RETURN-VALUE:X3J13-MAR-93
  yes
NTH-VALUE:ADD
  yes
OPTIMIZE-DEBUG-INFO:NEW-QUALITY
  yes
PACKAGE-CLUTTER:REDUCE
  yes
PACKAGE-DELETION:NEW-FUNCTION
  yes
PACKAGE-FUNCTION-CONSISTENCY:MORE-PERMISSIVE
  yes
PARSE-ERROR-STREAM:SPLIT-TYPES
  yes
PATHNAME-COMPONENT-CASE:KEYWORD-ARGUMENT
  yes
PATHNAME-COMPONENT-VALUE:SPECIFY
  no
PATHNAME-HOST-PARSING:RECOGNIZE-LOGICAL-HOST-NAMES
  yes when `CUSTOM:*PARSE-NAMESTRING-ANSI*` is non-`NIL`
PATHNAME-LOGICAL:ADD
  yes
PATHNAME-PRINT-READ:SHARPSIGN-P
  yes
PATHNAME-STREAM
  yes
PATHNAME-STREAM:FILES-OR-SYNONYM
  yes
PATHNAME-SUBDIRECTORY-LIST:NEW-REPRESENTATION
  yes
PATHNAME-SYMBOL
  yes when `CUSTOM:*PARSE-NAMESTRING-ANSI*` is non-`NIL`
PATHNAME-SYNTAX-ERROR-TIME:EXPLICITLY-VAGUE
  yes
PATHNAME-UNSPECIFIC-COMPONENT:NEW-TOKEN
  yes
PATHNAME-WILD:NEW-FUNCTIONS
  yes
PEEK-CHAR-READ-CHAR-ECHO:FIRST-READ-CHAR
  yes
PLIST-DUPLICATES:ALLOW
  yes
PRETTY-PRINT-INTERFACE
  yes
PRINC-READABLY:X3J13-DEC-91
  yes
PRINT-CASE-BEHAVIOR:CLARIFY
  yes
PRINT-CASE-PRINT-ESCAPE-INTERACTION:VERTICAL-BAR-RULE-NO-UPCASE
  yes
PRINT-CIRCLE-SHARED:RESPECT-PRINT-CIRCLE
  yes
PRINT-CIRCLE-STRUCTURE:USER-FUNCTIONS-WORK
  yes
PRINT-READABLY-BEHAVIOR:CLARIFY
  yes
PRINTER-WHITESPACE:JUST-ONE-SPACE
  yes
PROCLAIM-ETC-IN-COMPILE-FILE:NEW-MACRO
  yes
PUSH-EVALUATION-ORDER:FIRST-ITEM
  yes
PUSH-EVALUATION-ORDER:ITEM-FIRST
  yes
PUSHNEW-STORE-REQUIRED:UNSPECIFIED
  yes
QUOTE-SEMANTICS:NO-COPYING
  yes
RANGE-OF-COUNT-KEYWORD:NIL-OR-INTEGER
  yes, when `CUSTOM:*SEQUENCE-COUNT-ANSI*` is non-`NIL`; otherwise negative `:COUNT` values are not allowed.
RANGE-OF-START-AND-END-PARAMETERS:INTEGER-AND-INTEGER-NIL
  yes
READ-AND-WRITE-BYTES:NEW-FUNCTIONS
  yes
READ-CASE-SENSITIVITY:READTABLE-KEYWORDS
  yes
READ-MODIFY-WRITE-EVALUATION-ORDER:DELAYED-ACCESS-STORES
  no
READ-SUPPRESS-CONFUSING:GENERALIZE
  yes, except that `READ-DELIMITED-LIST` still constructs a `LIST`
READER-ERROR:NEW-TYPE
  yes
REAL-NUMBER-TYPE:X3J13-MAR-89
  yes
RECURSIVE-DEFTYPE:EXPLICITLY-VAGUE
  yes
REDUCE-ARGUMENT-EXTRACTION
  yes
REMF-DESTRUCTION-UNSPECIFIED:X3J13-MAR-89
  yes
REQUIRE-PATHNAME-DEFAULTS-AGAIN:X3J13-DEC-91
  yes
REQUIRE-PATHNAME-DEFAULTS-YET-AGAIN:RESTORE-ARGUMENT
  yes
REQUIRE-PATHNAME-DEFAULTS:ELIMINATE
  superseded by REQUIRE-PATHNAME-DEFAULTS-AGAIN:X3J13-DEC-91
REST-LIST-ALLOCATION:MAY-SHARE
  yes
RESULT-LISTS-SHARED:SPECIFY
  yes
RETURN-VALUES-UNSPECIFIED:SPECIFY
  yes
ROOM-DEFAULT-ARGUMENT:NEW-VALUE
  yes
SELF-MODIFYING-CODE:FORBID
  yes
SEQUENCE-TYPE-LENGTH:MUST-MATCH
  yes
SETF-APPLY-EXPANSION:IGNORE-EXPANDER
  yes
SETF-FIND-CLASS:ALLOW-NIL
  yes
SETF-FUNCTIONS-AGAIN:MINIMAL-CHANGES
  yes
SETF-GET-DEFAULT:EVALUATED-BUT-IGNORED
  yes
SETF-MACRO-EXPANSION:LAST
  yes
SETF-METHOD-VS-SETF-METHOD:RENAME-OLD-TERMS
  yes
SETF-MULTIPLE-STORE-VARIABLES:ALLOW
  yes
SETF-OF-APPLY:ONLY-AREF-AND-FRIENDS
  yes
SETF-OF-VALUES:ADD
  yes
SETF-SUB-METHODS:DELAYED-ACCESS-STORES
  yes
SHADOW-ALREADY-PRESENT
  yes
SHADOW-ALREADY-PRESENT:WORKS
  yes
SHARP-COMMA-CONFUSION:REMOVE
  no
SHARP-O-FOOBAR:CONSEQUENCES-UNDEFINED
  yes
SHARP-STAR-DELIMITER:NORMAL-DELIMITER
  yes
SHARPSIGN-PLUS-MINUS-PACKAGE:KEYWORD
  yes
SLOT-MISSING-VALUES:SPECIFY
  yes
SLOT-VALUE-METACLASSES:LESS-MINIMAL
  yes
SPECIAL-FORM-P-MISNOMER:RENAME
  yes
SPECIAL-TYPE-SHADOWING:CLARIFY
  yes
STANDARD-INPUT-INITIAL-BINDING:DEFINED-CONTRACTS
  yes
STANDARD-REPERTOIRE-GRATUITOUS:RENAME
  yes
STEP-ENVIRONMENT:CURRENT
  yes
STEP-MINIMAL:PERMIT-PROGN
  yes
STREAM-ACCESS:ADD-TYPES-ACCESSORS
  yes
STREAM-CAPABILITIES:INTERACTIVE-STREAM-P
  yes
STRING-COERCION:MAKE-CONSISTENT
  yes
STRING-OUTPUT-STREAM-BASHING:UNDEFINED
  yes
STRUCTURE-READ-PRINT-SYNTAX:KEYWORDS
  yes
SUBSEQ-OUT-OF-BOUNDS
  yes
SUBSEQ-OUT-OF-BOUNDS:IS-AN-ERROR
  yes
SUBSETTING-POSITION:NONE
  yes
SUBTYPEP-ENVIRONMENT:ADD-ARG
  yes
SUBTYPEP-TOO-VAGUE:CLARIFY-MORE
  yes
SXHASH-DEFINITION:SIMILAR-FOR-SXHASH
  yes
SYMBOL-MACROLET-DECLARE:ALLOW
  yes
SYMBOL-MACROLET-SEMANTICS:SPECIAL-FORM
  yes
SYMBOL-MACROLET-TYPE-DECLARATION:NO
  yes
SYMBOL-MACROS-AND-PROCLAIMED-SPECIALS:SIGNALS-AN-ERROR
  yes
SYMBOL-PRINT-ESCAPE-BEHAVIOR:CLARIFY
  yes
SYNTACTIC-ENVIRONMENT-ACCESS:RETRACTED-MAR91
  yes
TAGBODY-TAG-EXPANSION:NO
  yes
TAILP-NIL:T
  yes
TEST-NOT-IF-NOT:FLUSH-ALL
  yes, but no warning
THE-AMBIGUITY:FOR-DECLARATION
  yes
THE-VALUES:RETURN-NUMBER-RECEIVED
  yes
TIME-ZONE-NON-INTEGER:ALLOW
  yes
TYPE-DECLARATION-ABBREVIATION:ALLOW-ALL
  no
TYPE-OF-AND-PREDEFINED-CLASSES:TYPE-OF-HANDLES-FLOATS
  yes
TYPE-OF-AND-PREDEFINED-CLASSES:UNIFY-AND-EXTEND
  yes
TYPE-OF-UNDERCONSTRAINED:ADD-CONSTRAINTS
  yes
TYPE-SPECIFIER-ABBREVIATION:X3J13-JUN90-GUESS
  yes
UNDEFINED-VARIABLES-AND-FUNCTIONS:COMPROMISE
  yes
UNINITIALIZED-ELEMENTS:CONSEQUENCES-UNDEFINED
  yes, could add error checking
UNREAD-CHAR-AFTER-PEEK-CHAR:DONT-ALLOW
  yes
UNSOLICITED-MESSAGES:NOT-TO-SYSTEM-USER-STREAMS
  yes
VARIABLE-LIST-ASYMMETRY:SYMMETRIZE
  yes
WITH-ADDED-METHODS:DELETE
  yes
WITH-COMPILATION-UNIT:NEW-MACRO
  yes
WITH-OPEN-FILE-DOES-NOT-EXIST:STREAM-IS-NIL
  yes
WITH-OPEN-FILE-SETQ:EXPLICITLY-VAGUE
  yes
WITH-OPEN-FILE-STREAM-EXTENT:DYNAMIC-EXTENT
  yes
WITH-OUTPUT-TO-STRING-APPEND-STYLE:VECTOR-PUSH-EXTEND
  yes
WITH-STANDARD-IO-SYNTAX-READTABLE:X3J13-MAR-91
  yes

# Part II. Common Portable Extensions

## Chapter 29. Meta-Object Protocol

### Adapted from chapters 5 and 6 of [AMOP]

## 29.1. Introduction

The CLOS specification ([ANSI CL standard] Chanpter 7) describes the standard Programmer Interface for the Common Lisp Object System (CLOS). This document extends that specification by defining a metaobject protocol for CLOS - that is, a description of CLOS itself as an extensible CLOS program. In this description, the fundamental elements of CLOS programs (classes, slot definitions, generic functions, methods, specializers and method combinations) are represented by first-class objects. The behavior of CLOS is provided by these objects, or, more precisely, by methods specialized to the classes of these objects.

Because these objects represent pieces of CLOS programs, and because their behavior provides the behavior of the CLOS language itself, they are considered meta-level objects or metaobjects. The protocol followed by the metaobjects to provide the behavior of CLOS is called the CLOS “Metaobject Protocol” (MOP).

### 29.1.1. Notation

The description of functions follows the same form as used in the CLOS specification. The description of generic functions is similar to that in the CLOS specification, but some minor changes have been made in the way methods are presented.

The following is an example of the format for the syntax description of a generic function:

    (gf1 x y &OPTIONAL v &KEY k)

This description indicates that `gf1` is a generic function with two required parameters, `x` and `y`, an optional parameter `v` and a keyword parameter `k`.

The description of a generic function includes a description of its behavior. This provides the general behavior, or protocol of the generic function. All methods defined on the generic function, both portable and specified, must have behavior consistent with this description.

Every generic function described here is an instance of the class `STANDARD-GENERIC-FUNCTION` and uses the `STANDARD` method combination.

The description of a generic function also includes descriptions of the specified methods for that generic function. In the description of these methods, a method signature is used to describe the parameters and parameter specializers of each method. The following is an example of the format for a method signature:

    (gf1 (x CLASS) y &OPTIONAL v &KEY k)

This signature indicates that this primary method on the generic function `gf1` has two required parameters, named `x` and `y`. In addition, there is an optional parameter `v` and a keyword parameter `k`. This signature also indicates that the method's parameter specializers are the classes `CLASS` and `T`.

The description of each method includes a description of the behavior particular to that method.

An abbreviated syntax is used when referring to a method defined elsewhere in the document. This abbreviated syntax includes the name of the generic function, the qualifiers, and the parameter specializers. A reference to the method with the signature shown above is written as: ``gf1` (`CLASS` `T`)`.

### 29.1.2. Package

The package exporting the Meta-Object Protocol symbols is unspecified.

### Implementation dependent: only in CLISP

The symbols specified by the Meta-Object Protocol are exported from the package “CLOS” and `EXT:RE-EXPORT`ed from the package “EXT”.

The package exporting the Meta-Object Protocol symbols is different in other implementations: In SBCL it is the package “SB-MOP”; in Clozure CL it is the package “OPENMCL-MOP”.

## 29.2. Overview

### 29.2.1. Metaobjects

For each kind of program element there is a corresponding basic metaobject class . These are the classes: `CLASS`, `CLOS:SLOT-DEFINITION`, `GENERIC-FUNCTION`, `METHOD` and `METHOD-COMBINATION`. A metaobject class is a subclass of exactly one of these classes. The results are undefined if an attempt is made to define a `CLASS` that is a subclass of more than one basic metaobject class. A metaobject is an instance of a metaobject class.

Each metaobject represents one program element. Associated with each metaobject is the information required to serve its role. This includes information that might be provided directly in a user interface macro such as `DEFCLASS` or `DEFMETHOD`. It also includes information computed indirectly from other metaobjects such as that computed from class inheritance or the full set of methods associated with a generic function.

Much of the information associated with a metaobject is in the form of connections to other metaobjects. This interconnection means that the role of a metaobject is always based on that of other metaobjects. As an introduction to this interconnected structure, this section presents a partial enumeration of the kinds of information associated with each kind of metaobject. More detailed information is presented later.

#### 29.2.1.1. Classes

A class metaobject determines the structure and the default behavior of its instances. The following information is associated with class metaobjects:

- The name, if there is one, is available as an object.
- The direct subclasses, direct superclasses and class precedence list are available as lists of class metaobjects.
- The slots defined directly in the class are available as a list of direct slot definition metaobjects. The slots which are accessible in instances of the class are available as a list of effective slot definition metaobjects.
- The methods which use the class as a specializer, and the generic functions associated with those methods are available as lists of method and generic function metaobjects respectively.
- The documentation is available as a `STRING` or `NIL`.

See also Section 29.3, “Classes”

#### 29.2.1.2. Slot Definitions

A slot definition metaobject contains information about the definition of a slot. There are two kinds of slot definition metaobjects:

direct slot definition metaobject
  Used to represent the direct definition of a slot in a class. This corresponds roughly to the slot specifiers found in `DEFCLASS` forms.
effective slot definition metaobject
  Used to represent information, including inherited information, about a slot which is accessible in instances of a particular class.

Associated with each class metaobject is a list of direct slot definition metaobjects representing the slots defined directly in the class. Also associated with each class metaobject is a list of effective slot definition metaobjects representing the set of slots accessible in instances of that class.

The following information is associated with both direct and effective slot definitions metaobjects:

- The name, allocation, and type are available as forms that could appear in a `DEFCLASS` form.
- The initialization form, if there is one, is available as a form that could appear in a `DEFCLASS` form. The initialization form together with its lexical environment is available as a function of no arguments which, when called, returns the result of evaluating the initialization form in its lexical environment. This is called the initfunction of the slot.
- The slot filling initialization arguments are available as a list of symbols.
- The documentation is available as a `STRING` or `NIL`.

Certain other information is only associated with direct slot definition metaobjects. This information applies only to the direct definition of the slot in the class (it is not inherited).

- The function names of those generic functions for which there are automatically generated reader and writer methods. This information is available as lists of function names. Any accessors specified in the `DEFCLASS` form are broken down into their equivalent readers and writers in the direct slot definition.

Information, including inherited information, which applies to the definition of a slot in a particular class in which it is accessible is associated only with effective slot definition metaobjects.

- For certain slots, the location of the slot in instances of the class is available.

See also Section 29.4, “Slot Definitions”

#### 29.2.1.3. Generic Functions

A generic function metaobject contains information about a generic function over and above the information associated with each of the generic function's methods.

- The name is available as a function name.
- The methods associated with the generic function are available as a list of method metaobjects.
- The default class for this generic function's method metaobjects is available as a class metaobject.
- The lambda list is available as a `LIST`.
- The method combination is available as a method combination metaobject.
- The argument precedence order is available as a permutation of those symbols from the lambda list which name the required arguments of the generic function.

- The “declarations” are available as a list of declaration specifiers.

  ### Note

  There is a slight misnomer in the naming of functions and options in this document: Where the term “declaration” is used, actually a declaration specifier is meant.

- The documentation is available as a `STRING` or `NIL`.

See also Section 29.5, “Generic Functions”

#### 29.2.1.4. Methods

A method metaobject contains information about a specific `METHOD`.

- The qualifiers are available as a `LIST` of of non-`NIL` atoms.
- The lambda list is available as a `LIST`.
- The specializers are available as a list of specializer metaobjects.
- The function is available as a `FUNCTION`. This function can be applied to arguments and a list of next methods using `APPLY` or `FUNCALL`.
- When the method is associated with a generic function, that generic function metaobject is available. A method can be associated with at most one generic function at a time.
- The documentation is available as a `STRING` or `NIL`.

See also Section 29.6, “Methods”

#### 29.2.1.5. Specializers

A specializer metaobject represents the specializers of a `METHOD`. class metaobjects are themselves specializer metaobjects. A special kind of specializer metaobject is used for `EQL` specializers.

See also Section 29.8, “Specializers”

#### 29.2.1.6. Method Combinations

A method combination metaobject represents the information about the method combination being used by a generic function.

### Note

This document does not specify the structure of method combination metaobjects.

See also Section 29.9, “Method Combinations”

### 29.2.2. Inheritance Structure of Metaobject Classes

Figure 29.1. Inheritance structure of metaobject classes

The inheritance structure of the specified metaobject classes is shown in Table 29.1, “Direct Superclass Relationships Among The Specified Metaobject Classes”. The class of every class shown is `STANDARD-CLASS` except for the classes `T` and `FUNCTION`, which are instances of the class `BUILT-IN-CLASS`, and the classes `GENERIC-FUNCTION` and `STANDARD-GENERIC-FUNCTION`, which are instances of the class `CLOS:FUNCALLABLE-STANDARD-CLASS`.

Table 29.1. Direct Superclass Relationships Among The Specified Metaobject Classes

Metaobject Class | Abstract | Subclassable | Direct Superclasses
--- | --- | --- | ---
`STANDARD-OBJECT` | no | yes | (`T`)
`CLOS:FUNCALLABLE-STANDARD-OBJECT` | no | yes | (`STANDARD-OBJECT` `FUNCTION`)
`CLOS:METAOBJECT` | yes | no | (`STANDARD-OBJECT`)
`GENERIC-FUNCTION` | yes | no | (`CLOS:METAOBJECT` `CLOS:FUNCALLABLE-STANDARD-OBJECT`)
`STANDARD-GENERIC-FUNCTION` | no | yes | (`GENERIC-FUNCTION`)
`METHOD` | yes | no | (`CLOS:METAOBJECT`)
`STANDARD-METHOD` | no | yes | (`METHOD`)
`CLOS:STANDARD-ACCESSOR-METHOD` | yes | no | (`STANDARD-METHOD`)
`CLOS:STANDARD-READER-METHOD` | no | yes | (`CLOS:STANDARD-ACCESSOR-METHOD`)
`CLOS:STANDARD-WRITER-METHOD` | no | yes | (`CLOS:STANDARD-ACCESSOR-METHOD`)
`METHOD-COMBINATION` | yes | no | (`CLOS:METAOBJECT`)
`CLOS:SLOT-DEFINITION` | yes | no | (`CLOS:METAOBJECT`)
`CLOS:DIRECT-SLOT-DEFINITION` | yes | no | (`CLOS:SLOT-DEFINITION`)
`CLOS:EFFECTIVE-SLOT-DEFINITION` | yes | no | (`CLOS:SLOT-DEFINITION`)
`CLOS:STANDARD-SLOT-DEFINITION` | yes | no | (`CLOS:SLOT-DEFINITION`)
`CLOS:STANDARD-DIRECT-SLOT-DEFINITION` | no | yes | (`CLOS:STANDARD-SLOT-DEFINITION` `CLOS:DIRECT-SLOT-DEFINITION`)
`CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION` | no | yes | (`CLOS:STANDARD-SLOT-DEFINITION` `CLOS:EFFECTIVE-SLOT-DEFINITION`)
`CLOS:SPECIALIZER` | yes | no | (`CLOS:METAOBJECT`)
`CLOS:EQL-SPECIALIZER` | no | no | (`CLOS:SPECIALIZER`)
`CLASS` | yes | no | (`CLOS:SPECIALIZER`)
`BUILT-IN-CLASS` | no | no | (`CLASS`)
`CLOS:FORWARD-REFERENCED-CLASS` | no | no | (`CLASS`)
`STANDARD-CLASS` | no | yes | (`CLASS`)
`CLOS:FUNCALLABLE-STANDARD-CLASS` | no | yes | (`CLASS`)

Each class with a “yes” in the “Abstract” column is an abstract class and is not intended to be instantiated. The results are undefined if an attempt is made to make an instance of one of these classes with `MAKE-INSTANCE`.

Each class with a “yes” in the “Subclassable” column can be used as direct superclass for portable programs. It is not meaningful to subclass a class that has a “no” in this column.

### Implementation dependent: only in CLISP

The class `METHOD` is also subclassable: It is possible to create subclasses of `METHOD` that do not inherit from `STANDARD-METHOD`.

### Implementation dependent: only in CLISP and some other implementations

The class `CLOS:FUNCALLABLE-STANDARD-OBJECT`'s class precedence list contains `FUNCTION` before `STANDARD-OBJECT`, not after `STANDARD-OBJECT`. This is the most transparent way to realize the [ANSI CL standard] requirement (see the [ANSI CL standard] section 4.2.2 “Type Relationships”) that `GENERIC-FUNCTION`'s class precedence list contains `FUNCTION` before `STANDARD-OBJECT`.

The classes `STANDARD-CLASS`, `CLOS:STANDARD-DIRECT-SLOT-DEFINITION`, `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`, `STANDARD-METHOD`, `CLOS:STANDARD-READER-METHOD`, `CLOS:STANDARD-WRITER-METHOD` and `STANDARD-GENERIC-FUNCTION` are called standard metaobject classes. For each kind of metaobject, this is the class the user interface macros presented in the CLOS use by default. These are also the classes on which user specializations are normally based.

The classes `BUILT-IN-CLASS`, `CLOS:FUNCALLABLE-STANDARD-CLASS` and `CLOS:FORWARD-REFERENCED-CLASS` are special-purpose class metaobject classes. Built-in classes are instances of the class `BUILT-IN-CLASS`. The class `CLOS:FUNCALLABLE-STANDARD-CLASS` provides a special kind of instances described in Section 29.10.2, “Funcallable Instances”. When the definition of a class references another class which has not yet been defined, an instance of `CLOS:FORWARD-REFERENCED-CLASS` is used as a stand-in until the class is actually defined.

### Implementation of class `CLOS:FORWARD-REFERENCED-CLASS` in CLISP

The class `CLOS:FORWARD-REFERENCED-CLASS` is implemented in a way that fixes several flaws in the [AMOP] specification.

It is not a subclass of `CLASS` and `CLOS:SPECIALIZER`, just a subclass of `CLOS:METAOBJECT`, because forward references to classes are not classes and cannot be used as specializers of methods. An [AMOP] compatibility mode is provided, however, if you set the variable `CUSTOM:*FORWARD-REFERENCED-CLASS-MISDESIGN*` to `T`. In this mode, `CLOS:FORWARD-REFERENCED-CLASS` is formally a subclass of `CLASS` and `CLOS:SPECIALIZER`, but the behaviour of `CLOS:FORWARD-REFERENCED-CLASS` instances is the same.

The [AMOP] says that the first argument of `CLOS:ENSURE-CLASS-USING-CLASS` can be a `CLOS:FORWARD-REFERENCED-CLASS`. But from the description of `CLOS:ENSURE-CLASS`, it is clear that it can only be a class returned by `FIND-CLASS`, and [ANSI CL standard] `FIND-CLASS` cannot return a `CLOS:FORWARD-REFERENCED-CLASS`.

The [AMOP] says that `CLOS:ENSURE-CLASS-USING-CLASS` creates a `CLOS:FORWARD-REFERENCED-CLASS` for not-yet-defined class symbols among the direct-superclasses list. But this leads to many `CLOS:FORWARD-REFERENCED-CLASS` with the same name (since they cannot be stored and retrieved through `FIND-CLASS`), and since `CHANGE-CLASS` preserves the `EQ`-ness, after the class is defined, we have many class objects with the same name.

In the direct-superclasses list of non-finalized classes, `CLOS:FORWARD-REFERENCED-CLASS` instances can occur, denoting classes that have not yet been defined. When or after such a class gets defined, the `CLOS:FORWARD-REFERENCED-CLASS` instance is replaced with the real class. CLISP uses simple object replacement, not `CHANGE-CLASS`, in this process.

The class `STANDARD-OBJECT` is the default direct superclass of the class `STANDARD-CLASS`. When an instance of the class `STANDARD-CLASS` is created, and no direct superclasses are explicitly specified, it defaults to the class `STANDARD-OBJECT`. In this way, any behavior associated with the class `STANDARD-OBJECT` will be inherited, directly or indirectly, by all instances of the class `STANDARD-CLASS`. A subclass of `STANDARD-CLASS` may have a different class as its default direct superclass, but that class must be a subclass of the class `STANDARD-OBJECT`.

The same is true for `CLOS:FUNCALLABLE-STANDARD-CLASS` and `CLOS:FUNCALLABLE-STANDARD-OBJECT`.

The class `CLOS:SPECIALIZER` captures only the most basic behavior of method specializers, and is not itself intended to be instantiated. The class `CLASS` is a direct subclass of `CLOS:SPECIALIZER` reflecting the property that classes by themselves can be used as method specializers. The class `CLOS:EQL-SPECIALIZER` is used for `EQL` specializers.

#### 29.2.2.1. Implementation and User Specialization

The purpose of the Metaobject Protocol is to provide users with a powerful mechanism for extending and customizing the basic behavior of the CLOS. As an object-oriented description of the basic CLOS behavior, the Metaobject Protocol makes it possible to create these extensions by defining specialized subclasses of existing metaobject classes.

The Metaobject Protocol provides this capability without interfering with the implementor's ability to develop high-performance implementations. This balance between user extensibility and implementor freedom is mediated by placing explicit restrictions on each. Some of these restrictions are general---they apply to the entire class graph and the applicability of all methods. These are presented in this section.

The following additional terminology is used to present these restrictions:

- Metaobjects are divided into three categories. Those defined in this document are called specified ; those defined by an implementation but not mentioned in this document are called implementation-specific ; and those defined by a portable program are called portable .
- A class `i` is interposed between two other classes `k1` and `k2` if and only if there is some path, following direct superclasses, from the class `k1` to the class `k2` which includes `i`.
- A method is specialized to a class if and only if that class is in the list of specializers associated with the method; and the method is in the list of methods associated with some generic function.
- In a given implementation, a specified method is said to have been promoted if and only if the specializers of the method, `x1` ... `xn`, are defined in this specification as the classes `k1` ... `kn`, but in the implementation, one or more of the specializers `xl`, is a superclass of the class given in the specification `kl`.

- For a given generic function and set of arguments, a method `k2` extends a method `k1` if and only if:

  1. `k1` and `k2` are both associated with the given generic function
  2. `k1` and `k2` are both applicable to the given arguments,
  3. the specializers and qualifiers of the methods are such that when the generic function is called, `k2` is executed before `k1`,
  4. `k1` will be executed if and only if `CALL-NEXT-METHOD` is invoked from within the body of `k2` and
  5. `CALL-NEXT-METHOD` is invoked from within the body of `k2`, thereby causing `k1` to be executed.

- For a given generic function and set of arguments, a method `k2` overrides a method `k1` if and only if conditions i through iv above hold and, instead of v,

  6. `CALL-NEXT-METHOD` is not invoked from within the body of `k2`, thereby preventing `k1` from being executed.

##### 29.2.2.1.1. Restrictions on Portable Programs

Portable programs are allowed to define subclasses of specified classes, and are permitted to define methods on specified generic functions, with the following restrictions:

- Portable programs must not redefine any specified classes, generic functions, methods or method combinations. Any method defined by a portable program on a specified generic function must have at least one specializer that is neither a specified class nor an `EQL` specializer whose associated value is an instance of a specified class.
- Portable programs may define methods that extend specified methods unless the description of the specified method explicitly prohibits this. Unless there is a specific statement to the contrary, these extending methods must return whatever value was returned by the call to `CALL-NEXT-METHOD`.

- Portable programs may define methods that override specified methods only when the description of the specified method explicitly allows this. Typically, when a method is allowed to be overridden, a small number of related methods will need to be overridden as well.

  An example of this is the specified methods on the generic functions `CLOS:ADD-DEPENDENT`, `CLOS:REMOVE-DEPENDENT` and `CLOS:MAP-DEPENDENTS`. Overriding a specified method on one of these generic functions requires that the corresponding method on the other two generic functions be overridden as well.

- Portable methods on specified generic functions specialized to portable metaobject classes must be defined before any instances of those classes (or any subclasses) are created, either directly or indirectly by a call to `MAKE-INSTANCE`. Methods can be defined after instances are created by `ALLOCATE-INSTANCE` however. Portable metaobject classes cannot be redefined.

  ### Note

  The purpose of this last restriction is to permit implementations to provide performance optimizations by analyzing, at the time the first instance of a metaobject class is initialized, what portable methods will be applicable to it. This can make it possible to optimize calls to those specified generic functions which would have no applicable portable methods.

  ### Implementation dependent: only in CLISP

  When a metaobject class is redefined, CLISP issues a `WARNING` that the redefinition has no effect. To avoid this warning, place all metaobject class definitions in a separate file, compile it in a separate session (because `DEFCLASS` in CLISP is evaluated at compile time too; see Section 29.2.3.2, “Compile-file Processing of Specific User Interface Macros”), and then `LOAD` it only once per session.

The results are undefined if any of these restrictions are violated.

### Note

The specification technology used in this document needs further development. The concepts of object-oriented protocols and subclass specialization are intuitively familiar to programmers of object-oriented systems; the protocols presented here fit quite naturally into this framework. Nonetheless, in preparing this document, we have found it difficult to give specification-quality descriptions of the protocols in a way that makes it clear what extensions users can and cannot write. Object-oriented protocol specification is inherently about specifying leeway, and this seems difficult using current technology.

##### 29.2.2.1.2. Restrictions on Implementations

Implementations are allowed latitude to modify the structure of specified classes and methods. This includes: the interposition of implementation-specific classes; the promotion of specified methods; and the consolidation of two or more specified methods into a single method specialized to interposed classes.

Any such modifications are permitted only so long as for any portable class `k` that is a subclass of one or more specified classes `k1` ... `kn`, the following conditions are met:

- In the actual class precedence list of `k`, the classes `k1` ... `kn` must appear in the same order as they would have if no implementation-specific modifications had been made.
- The method applicability of any specified generic function must be the same in terms of behavior as it would have been had no implementation-specific changes been made. This includes specified generic functions that have had portable methods added. In this context, the expression “the same in terms of behavior” means that methods with the same behavior as those specified are applicable, and in the same order.
- No portable class `k` may inherit, by virtue of being a direct or indirect subclass of a specified class, any slot for which the name is a symbol accessible in the “COMMON-LISP-USER” package or exported by any package defined in the [ANSI CL standard].
- Implementations are free to define implementation-specific before- and after-methods on specified generic functions. Implementations are also free to define implementation-specific around-methods with extending behavior.

### 29.2.3. Processing of the User Interface Macros

A list in which the first element is one of the symbols `DEFCLASS`, `DEFMETHOD`, `DEFGENERIC`, `DEFINE-METHOD-COMBINATION`, `CLOS:GENERIC-FUNCTION`, `CLOS:GENERIC-FLET` or `CLOS:GENERIC-LABELS`, and which has proper syntax for that macro is called a user interface macro form. This document provides an extended specification of the `DEFCLASS`, `DEFMETHOD` and `DEFGENERIC` macros.

The user interface macros `DEFCLASS`, `DEFGENERIC` and `DEFMETHOD` can be used not only to define metaobjects that are instances of the corresponding standard metaobject class, but also to define metaobjects that are instances of appropriate portable metaobject classes. To make it possible for portable metaobject classes to properly process the information appearing in the macro form, this document provides a limited specification of the processing of these macro forms.

User interface macro forms can be evaluated or compiled and later executed. The effect of evaluating or executing a user interface macro form is specified in terms of calls to specified functions and generic functions which provide the actual behavior of the macro. The arguments received by these functions and generic functions are derived in a specified way from the macro form.

Converting a user interface macro form into the arguments to the appropriate functions and generic functions has two major aspects: the conversion of the macro argument syntax into a form more suitable for later processing, and the processing of macro arguments which are forms to be evaluated (including method bodies).

In the syntax of the `DEFCLASS` macro, the `initform` and `default-initarg-initial-value-form` arguments are forms which will be evaluated one or more times after the macro form is evaluated or executed. Special processing must be done on these arguments to ensure that the lexical scope of the forms is captured properly. This is done by building a function of zero arguments which, when called, returns the result of evaluating the form in the proper lexical environment.

In the syntax of the `DEFMETHOD` macro the `forms` argument is a list of forms that comprise the body of the method definition. This list of forms must be processed specially to capture the lexical scope of the macro form. In addition, the lexical functions available only in the body of methods must be introduced. To allow this and any other special processing (such as slot access optimization), a specializable protocol is used for processing the body of methods. This is discussed in Section 29.6.3.1.1, “Processing Method Bodies”.

#### 29.2.3.1. Compile-file Processing of the User Interface Macros

It is a common practice for Common Lisp compilers, while processing a file or set of files, to maintain information about the definitions that have been compiled so far. Among other things, this makes it possible to ensure that a global macro definition (`DEFMACRO` form) which appears in a file will affect uses of the macro later in that file. This information about the state of the compilation is called the `COMPILE-FILE` environment.

When compiling files containing CLOS definitions, it is useful to maintain certain additional information in the `COMPILE-FILE` environment. This can make it possible to issue various kinds of warnings (e.g., lambda list congruence) and to do various performance optimizations that would not otherwise be possible.

At this time, there is such significant variance in the way existing Common Lisp implementations handle `COMPILE-FILE` environments that it would be premature to specify this mechanism. Consequently, this document specifies only the behavior of evaluating or executing user interface macro forms. What functions and generic functions are called during `COMPILE-FILE` processing of a user interface macro form is not specified. Implementations are free to define and document their own behavior. Users may need to check implementation-specific behavior before attempting to compile certain portable programs.

#### 29.2.3.2. Compile-file Processing of Specific User Interface Macros

`DEFCLASS`

  Section 29.3.1, “Macro `DEFCLASS`”

  ### Implementation dependent: only in CLISP

  CLISP evaluates `DEFCLASS` forms also at compile time.

`DEFMETHOD`

  Section 29.6.3.1, “Macro `DEFMETHOD`”

  ### Implementation dependent: only in CLISP

  CLISP does not evaluate `DEFMETHOD` forms at compile time except as necessary for signature checking.

`DEFGENERIC`

  Section 29.5.3.1, “Macro `DEFGENERIC`”

  ### Implementation dependent: only in CLISP

  CLISP does not evaluate `DEFGENERIC` forms at compile time except as necessary for signature checking.

### 29.2.4. Metaobject Initialization Protocol

Like other objects, metaobjects can be created by calling `MAKE-INSTANCE`. The initialization arguments passed to `MAKE-INSTANCE` are used to initialize the metaobject in the usual way. The set of legal initialization arguments, and their interpretation, depends on the kind of metaobject being created. Implementations and portable programs are free to extend the set of legal initialization arguments. Detailed information about the initialization of each kind of metaobject are provided in the appropriate sections:

- Section 29.3.5.1, “Initialization of class metaobjects”
- Section 29.3.5.2, “Reinitialization of class metaobjects”
- Section 29.5.3.3, “Initialization of generic function metaobjects”
- Section 29.3.4, “Class Finalization Protocol”
- Section 29.10.1, “Instance Structure Protocol”
- Section 29.10.2, “Funcallable Instances”
- Section 29.5.3.2, “Generic Function Invocation Protocol”
- Section 29.11, “Dependent Maintenance”

## 29.3. Classes

### 29.3.1. Macro `DEFCLASS`

The evaluation or execution of a `DEFCLASS` form results in a call to the `CLOS:ENSURE-CLASS` function. The arguments received by `CLOS:ENSURE-CLASS` are derived from the `DEFCLASS` form in a defined way. The exact macro-expansion of the `DEFCLASS` form is not defined, only the relationship between the arguments to the `DEFCLASS` macro and the arguments received by the `CLOS:ENSURE-CLASS` function. Examples of typical `DEFCLASS` forms and sample expansions are shown in the following two examples:

A `DEFCLASS` form with standard slot and class options and an expansion of it that would result in the proper call to `CLOS:ENSURE-CLASS`.

    (defclass plane (moving-object graphics-object)
      ((altitude :initform 0 :accessor plane-altitude)
       (speed))
      (:default-initargs :engine *jet*))

    (ensure-class 'plane
      ':direct-superclasses '(moving-object graphics-object)
      ':direct-slots (list (list ':name 'altitude
                                 ':initform '0
                                 ':initfunction #'(lambda () 0)
                                 ':readers '(plane-altitude)
                                 ':writers '((setf plane-altitude)))
                           (list ':name 'speed))
      ':direct-default-initargs (list (list ':engine
                                            '*jet*
                                            #'(lambda () *jet*))))

A `DEFCLASS` form with non-standard class and slot options, and an expansion of it which results in the proper call to `CLOS:ENSURE-CLASS`. Note that the order of the slot options has not affected the order of the properties in the canonicalized slot specification, but has affected the order of the elements in the lists which are the values of those properties.

    (defclass sst (plane)
      ((mach mag-step 2
             locator sst-mach
             locator mach-location
             :reader mach-speed
             :reader mach))
      (:metaclass faster-class)
      (another-option foo bar))

    (ensure-class 'sst
      ':direct-superclasses '(plane)
      ':direct-slots (list (list ':name 'mach
                                 ':readers '(mach-speed mach)
                                 'mag-step '2
                                 'locator '(sst-mach mach-location)))
      ':metaclass 'faster-class
      'another-option '(foo bar))

- The `name` argument to `DEFCLASS` becomes the value of the first argument to `CLOS:ENSURE-CLASS`. This is the only positional argument accepted by `CLOS:ENSURE-CLASS`; all other arguments are keyword arguments.
- The `:DIRECT-SUPERCLASSES` argument to `DEFCLASS` becomes the value of the `:DIRECT-SUPERCLASSES` keyword argument to `CLOS:ENSURE-CLASS`.

- The `:DIRECT-SLOTS` argument to `DEFCLASS` becomes the value of the `:DIRECT-SLOTS` keyword argument to `CLOS:ENSURE-CLASS`. Special processing of this value is done to regularize the form of each slot specification and to properly capture the lexical scope of the initialization forms. This is done by converting each slot specification to a property list called a canonicalized slot specification. The resulting list of canonicalized slot specifications is the value of the `:DIRECT-SLOTS` keyword argument.

  Canonicalized slot specifications are later used as the keyword arguments to a generic function which will, in turn, pass them to `MAKE-INSTANCE` for use as a set of initialization arguments. Each canonicalized slot specification is formed from the corresponding slot specification as follows:

  - The name of the slot is the value of the `:NAME` property. This property appears in every canonicalized slot specification.
  - When the `:INITFORM` slot option is present in the slot specification, then both the `:INITFORM` and `:INITFUNCTION` properties are present in the canonicalized slot specification. The value of the `:INITFORM` property is the initialization form. The value of the `:INITFUNCTION` property is a function of zero arguments which, when called, returns the result of evaluating the initialization form in its proper lexical environment.
  - If the `:INITFORM` slot option is not present in the slot specification, then either the `:INITFUNCTION` property will not appear, or its value will be false. In such cases, the value of the `:INITFORM` property, or whether it appears, is unspecified.
  - The value of the `:INITARGS` property is a list of the values of each `:INITARG` slot option. If there are no `:INITARG` slot options, then either the `:INITARGS` property will not appear or its value will be the empty list.
  - The value of the `:READERS` property is a list of the values of each `:READER` and `:ACCESSOR` slot option. If there are no `:READER` or `:ACCESSOR` slot options, then either the `:READERS` property will not appear or its value will be the empty list.
  - The value of the `:WRITERS` property is a list of the values specified by each `:WRITER` and `:ACCESSOR` slot option. The value specified by a `:WRITER` slot option is just the value of the slot option. The value specified by an `:ACCESSOR` slot option is a two element list: the first element is the symbol `SETF`, the second element is the value of the slot option. If there are no `:WRITER` or `:ACCESSOR` slot options, then either the `:WRITERS` property will not appear or its value will be the empty list.
  - The value of the `:DOCUMENTATION` property is the value of the `:DOCUMENTATION` slot option. If there is no `:DOCUMENTATION` slot option, then either the `:DOCUMENTATION` property will not appear or its value will be false.
  - All other slot options appear as the values of properties with the same name as the slot option. Note that this includes not only the remaining standard slot options (`:ALLOCATION` and `:TYPE`), but also any other options and values appearing in the slot specification. If one of these slot options appears more than once, the value of the property will be a list of the specified values.
  - An implementation is free to add additional properties to the canonicalized slot specification provided these are not symbols accessible in the “COMMON-LISP-USER” package, or exported by any package defined in the [ANSI CL standard].

- The `:DEFAULT-INITARGS` class option, if it is present in the `DEFCLASS` form, becomes the value of the `:DIRECT-DEFAULT-INITARGS` keyword argument to `CLOS:ENSURE-CLASS`. Special processing of this value is done to properly capture the lexical scope of the default value forms. This is done by converting each default initarg in the class option into a canonicalized default initialization argument. The resulting list of canonicalized default initialization arguments is the value of the `:DIRECT-DEFAULT-INITARGS` keyword argument to `CLOS:ENSURE-CLASS`.

  A canonicalized default initarg is a list of three elements. The first element is the name; the second is the actual form itself; and the third is a function of zero arguments which, when called, returns the result of evaluating the default value form in its proper lexical environment.

  ### Implementation dependent: only in CLISP

  If a `:DEFAULT-INITARGS` class option is not present in the `DEFCLASS` form, `:DIRECT-DEFAULT-INITARGS` `NIL` is passed to `CLOS:ENSURE-CLASS`.

  This is needed to fulfill the [ANSI CL standard] requirement (see Section 4.6, “Redefining Classes sec_4-3-6”) that the resulting `CLASS` object reflects the `DEFCLASS` form.

- The `:METACLASS` class option, if it is present in the `DEFCLASS` form, becomes the value of the `:METACLASS` keyword argument to `CLOS:ENSURE-CLASS`.

  ### Implementation dependent: only in CLISP

  If a `:METACLASS` class option is not present in the `DEFCLASS` form, `:METACLASS` `STANDARD-CLASS` is passed to `CLOS:ENSURE-CLASS`.

  This is needed to fulfill the [ANSI CL standard] requirement (see Section 4.6, “Redefining Classes sec_4-3-6”) that the resulting `CLASS` object reflects the `DEFCLASS` form.

- The `:DOCUMENTATION` class option, if it is present in the `DEFCLASS` form, becomes the value of the `:DOCUMENTATION` keyword argument to `CLOS:ENSURE-CLASS`.

  ### Implementation dependent: only in CLISP

  If a `:DOCUMENTATION` class option is not present in the `DEFCLASS` form, `:DIRECT-DEFAULT-INITARGS` `NIL` is passed to `CLOS:ENSURE-CLASS`.

  This is needed to fulfill the [ANSI CL standard] requirement (see Section 4.6, “Redefining Classes sec_4-3-6”) that the resulting `CLASS` object reflects the `DEFCLASS` form.

- Any other class options become the value of keyword arguments with the same name. The value of the keyword argument is the tail of the class option. An `ERROR` is `SIGNAL`ed if any class option appears more than once in the `DEFCLASS` form.

  ### Implementation dependent: only in CLISP

  The default initargs of the `:METACLASS` are added at the end of the list of arguments to pass to `CLOS:ENSURE-CLASS`.

  This is needed to fulfill the [ANSI CL standard] requirement (see Section 4.6, “Redefining Classes sec_4-3-6”) that the resulting `CLASS` object reflects the `DEFCLASS` form.

In the call to `CLOS:ENSURE-CLASS`, every element of its arguments appears in the same left-to-right order as the corresponding element of the `DEFCLASS` form, except that the order of the properties of canonicalized slot specifications is unspecified. The values of properties in canonicalized slot specifications do follow this ordering requirement. Other ordering relationships in the keyword arguments to `CLOS:ENSURE-CLASS` are unspecified.

The result of the call to `CLOS:ENSURE-CLASS` is returned as the result of evaluating or executing the `DEFCLASS` form.

### 29.3.2. Inheritance Structure of class metaobject Classes

Figure 29.2. Inheritance structure of class metaobject classes

### 29.3.3. Introspection: Readers for class metaobjects

In this and the following sections, the “reader” generic functions which simply return information associated with a particular kind of metaobject are presented together. General information is presented first, followed by a description of the purpose of each, and ending with the specified methods for these generic functions.

The reader generic functions which simply return information associated with class metaobjects are presented together in this section.

Each of the reader generic functions for class metaobjects has the same syntax, accepting one required argument called `class`, which must be a class metaobject; otherwise, an `ERROR` is `SIGNAL`ed. An `ERROR` is also `SIGNAL`ed if the class metaobject has not been initialized.

These generic functions can be called by the user or the implementation.

For any of these generic functions which returns a list, such lists will not be mutated by the implementation. The results are undefined if a portable program allows such a list to be mutated.

#### 29.3.3.1. Generic Function `CLASS-NAME`

##### `(`CLASS-NAME` `class`)`

Returns the name of `class`. This value can be any Lisp object, but is usually a symbol, or `NIL` if the class has no name. This is the defaulted value of the `:NAME` initialization argument that was associated with the class during initialization or reinitialization. (Also see `(SETF CLASS-NAME)`.)

#### 29.3.3.2. Generic Function `CLOS:CLASS-DIRECT-SUPERCLASSES`

##### `(`CLOS:CLASS-DIRECT-SUPERCLASSES` `class`)`

Returns a list of the direct superclasses of `class`. The elements of this list are class metaobjects. The empty list is returned if `class` has no direct superclasses. This is the defaulted value of the `:DIRECT-SUPERCLASSES` initialization argument that was associated with the class during initialization or reinitialization.

### Implementation dependent: only in CLISP

For a class that has not yet been finalized, the returned list may contain `CLOS:FORWARD-REFERENCED-CLASS` instances as placeholder for classes that were not yet defined when finalization of the class was last attempted.

#### 29.3.3.3. Generic Function `CLOS:CLASS-DIRECT-SLOTS`

##### `(`CLOS:CLASS-DIRECT-SLOTS` `class`)`

Returns a set of the direct slots of `class`. The elements of this set are direct slot definition metaobjects. If the class has no direct slots, the empty set is returned. This is the defaulted value of the `:DIRECT-SLOTS` initialization argument that was associated with the class during initialization and reinitialization.

#### 29.3.3.4. Generic Function `CLOS:CLASS-DIRECT-DEFAULT-INITARGS`

##### `(`CLOS:CLASS-DIRECT-DEFAULT-INITARGS` `class`)`

Returns a list of the direct default initialization arguments for `class`. Each element of this list is a canonicalized default initialization argument. The empty list is returned if `class` has no direct default initialization arguments. This is the defaulted value of the `:DIRECT-DEFAULT-INITARGS` initialization argument that was associated with the class during initialization or reinitialization.

#### 29.3.3.5. Generic Function `CLOS:CLASS-PRECEDENCE-LIST`

##### `(`CLOS:CLASS-PRECEDENCE-LIST` `class`)`

Returns the class precedence list of `class`. The elements of this list are class metaobjects.

During class finalization `CLOS:FINALIZE-INHERITANCE` calls `CLOS:COMPUTE-CLASS-PRECEDENCE-LIST` to compute the class precedence list of the class. That value is associated with the class metaobject and is returned by `CLOS:CLASS-PRECEDENCE-LIST`.

This generic function `SIGNAL`s an `ERROR` if `class` has not been finalized.

#### 29.3.3.6. Generic Function `CLOS:CLASS-DIRECT-SUBCLASSES`

##### `(`CLOS:CLASS-DIRECT-SUBCLASSES` `class`)`

Returns a set of the direct subclasses of `class`. The elements of this set are class metaobjects that all mention this class among their direct superclasses. The empty set is returned if `class` has no direct subclasses. This value is maintained by the generic functions `CLOS:ADD-DIRECT-SUBCLASS` and `CLOS:REMOVE-DIRECT-SUBCLASS`.

### Implementation dependent: only in CLISP

The set of direct subclasses of a class is internally managed as a `EXT:WEAK-LIST`. Therefore the existence of the `CLOS:CLASS-DIRECT-SUBCLASSES` function does not prevent otherwise unreferenced classes from being garbage-collected.

#### 29.3.3.7. Generic Function `CLOS:CLASS-SLOTS`

##### `(`CLOS:CLASS-SLOTS` `class`)`

Returns a possibly empty set of the slots accessible in instances of `class`. The elements of this set are effective slot definition metaobjects.

During class finalization `CLOS:FINALIZE-INHERITANCE` calls `CLOS:COMPUTE-SLOTS` to compute the slots of the class. That value is associated with the class metaobject and is returned by `CLOS:CLASS-SLOTS`.

This generic function `SIGNAL`s an `ERROR` if `class` has not been finalized.

#### 29.3.3.8. Generic Function `CLOS:CLASS-DEFAULT-INITARGS`

##### `(`CLOS:CLASS-DEFAULT-INITARGS` `class`)`

Returns a list of the default initialization arguments for `class`. Each element of this list is a canonicalized default initialization argument. The empty list is returned if `class` has no default initialization arguments.

During finalization `CLOS:FINALIZE-INHERITANCE` calls `CLOS:COMPUTE-DEFAULT-INITARGS` to compute the default initialization arguments for the class. That value is associated with the class metaobject and is returned by `CLOS:CLASS-DEFAULT-INITARGS`.

This generic function `SIGNAL`s an `ERROR` if `class` has not been finalized.

#### 29.3.3.9. Generic Function `CLOS:CLASS-FINALIZED-P`

##### `(`CLOS:CLASS-FINALIZED-P` `class`)`

Returns true if `class` has been finalized. Returns false otherwise. Also returns false if the `class` has not been initialized.

#### 29.3.3.10. Generic Function `CLOS:CLASS-PROTOTYPE`

##### `(`CLOS:CLASS-PROTOTYPE` `class`)`

Returns a prototype instance of `class`. Whether the instance is initialized is not specified. The results are undefined if a portable program modifies the binding of any slot of a prototype instance.

This generic function `SIGNAL`s an `ERROR` if `class` has not been finalized.

This allows non-consing[3] access to slots with allocation `:CLASS`:

    (defclass counter ()
      ((count :allocation :class :initform 0 :reader how-many)))
    (defmethod initialize-instance :after ((obj counter) &rest args)
      (incf (slot-value obj 'count)))
    (defclass counted-object (counter) ((name :initarg :name)))

Now one can find out how many `COUNTED-OBJECT`s have been created by using `(HOW-MANY (`CLOS:CLASS-PROTOTYPE` (`FIND-CLASS` 'COUNTER)))`:

    (MAKE-INSTANCE 'counted-object :name 'foo)
    ⇒ #<COUNTED-OBJECT #x203028C9>
    (HOW-MANY (CLOS:CLASS-PROTOTYPE (FIND-CLASS 'counter)))
    ⇒ 1
    (MAKE-INSTANCE 'counted-object :name 'bar)
    ⇒ #<COUNTED-OBJECT #x20306CB1>
    (HOW-MANY (CLOS:CLASS-PROTOTYPE (FIND-CLASS 'counter)))
    ⇒ 2

#### 29.3.3.11. Methods

The specified methods for the class metaobject reader generic functions are presented below.

Each entry in the table indicates a method on one of the reader generic functions, specialized to a specified class. The number in each entry is a reference to the full description of the method. The full descriptions appear after the table.

Generic Function | `STANDARD-CLASS`, `CLOS:FUNCALLABLE-STANDARD-CLASS` | `CLOS:FORWARD-REFERENCED-CLASS` | `BUILT-IN-CLASS`
--- | --- | --- | ---
`CLASS-NAME` | 1 | 1 | 8
`CLOS:CLASS-DIRECT-SUPERCLASSES` | 1 | 4 | 7
`CLOS:CLASS-DIRECT-SLOTS` | 1 | 4 | 4
`CLOS:CLASS-DIRECT-DEFAULT-INITARGS` | 1 | 4 | 4
`CLOS:CLASS-PRECEDENCE-LIST` | 2 | 3 | 7
`CLOS:CLASS-DIRECT-SUBCLASSES` | 9 | 9 | 7
`CLOS:CLASS-SLOTS` | 2 | 3 | 4
`CLOS:CLASS-DEFAULT-INITARGS` | 2 | 3 | 4
`CLOS:CLASS-FINALIZED-P` | 2 | 6 | 5
`CLOS:CLASS-PROTOTYPE` | 10 | 10 | 10

Class Reader Methods

1. This method returns the value which was associated with the class metaobject during initialization or reinitialization.
2. This method returns the value associated with the class metaobject by ``CLOS:FINALIZE-INHERITANCE` (`STANDARD-CLASS`)` or ``CLOS:FINALIZE-INHERITANCE` (`CLOS:FUNCALLABLE-STANDARD-CLASS`)`
3. This method `SIGNAL`s an `ERROR`.
4. This method returns the empty list.
5. This method returns true.
6. This method returns false.
7. This method returns a value derived from the information in Table 29.1, “Direct Superclass Relationships Among The Specified Metaobject Classes”, except that implementation-specific modifications are permitted as described in Section 29.2.2.1, “Implementation and User Specialization”.
8. This method returns the name of the built-in class.
9. This method returns a value which is maintained by ``CLOS:ADD-DIRECT-SUBCLASS`(`CLASS` `CLASS`)` and ``CLOS:REMOVE-DIRECT-SUBCLASS` (`CLASS` `CLASS`)`. This method can be overridden only if those methods are overridden as well.
10. No behavior is specified for this method beyond that which is specified for the generic function.

### 29.3.4. Class Finalization Protocol

Class finalization is the process of computing the information a class inherits from its superclasses and preparing to actually allocate instances of the class. The class finalization process includes computing the class's class precedence list, the full set of slots accessible in instances of the class and the full set of default initialization arguments for the class. These values are associated with the class metaobject and can be accessed by calling the appropriate reader. In addition, the class finalization process makes decisions about how instances of the class will be implemented.

To support forward-referenced superclasses, and to account for the fact that not all classes are actually instantiated, class finalization is not done as part of the initialization of the class metaobject. Instead, finalization is done as a separate protocol, invoked by calling the generic function `CLOS:FINALIZE-INHERITANCE`. The exact point at which `CLOS:FINALIZE-INHERITANCE` is called depends on the class of the class metaobject; for `STANDARD-CLASS` it is called sometime after all the classes superclasses are defined, but no later than when the first instance of the class is allocated (by `ALLOCATE-INSTANCE`).

The first step of class finalization is computing the class precedence list. Doing this first allows subsequent steps to access the class precedence list. This step is performed by calling the generic function `CLOS:COMPUTE-CLASS-PRECEDENCE-LIST`. The value returned from this call is associated with the class metaobject and can be accessed by calling the `CLOS:CLASS-PRECEDENCE-LIST` generic function.

The second step is computing the full set of slots that will be accessible in instances of the class. This step is performed by calling the generic function `CLOS:COMPUTE-SLOTS`. The result of this call is a list of effective slot definition metaobjects. This value is associated with the class metaobject and can be accessed by calling the `CLOS:CLASS-SLOTS` generic function.

The behavior of `CLOS:COMPUTE-SLOTS` is itself layered, consisting of calls to `CLOS:EFFECTIVE-SLOT-DEFINITION-CLASS` and `CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION`.

The final step of class finalization is computing the full set of initialization arguments for the class. This is done by calling the generic function `CLOS:COMPUTE-DEFAULT-INITARGS`. The value returned by this generic function is associated with the class metaobject and can be accessed by calling `CLOS:CLASS-DEFAULT-INITARGS`.

If the class was previously finalized, `CLOS:FINALIZE-INHERITANCE` may call `MAKE-INSTANCES-OBSOLETE`. The circumstances under which this happens are described in the [ANSI CL standard] section Section 4.6, “Redefining Classes sec_4-3-6”.

Forward-referenced classes, which provide a temporary definition for a class which has been referenced but not yet defined, can never be finalized. An `ERROR` is `SIGNAL`ed if `CLOS:FINALIZE-INHERITANCE` is called on a forward-referenced class.

### 29.3.5. Class Initialization

#### 29.3.5.1. Initialization of class metaobjects

A class metaobject can be created by calling `MAKE-INSTANCE`. The initialization arguments establish the definition of the class. A class metaobject can be redefined by calling `REINITIALIZE-INSTANCE`. Some classes of class metaobject do not support redefinition; in these cases, `REINITIALIZE-INSTANCE` `SIGNAL`s an `ERROR`.

Initialization of a class metaobject must be done by calling `MAKE-INSTANCE` and allowing it to call `INITIALIZE-INSTANCE`. Reinitialization of a class metaobject must be done by calling `REINITIALIZE-INSTANCE`. Portable programs must not

- ... call `INITIALIZE-INSTANCE` directly to initialize a class metaobject;
- ... call `SHARED-INITIALIZE` directly to initialize or reinitialize a class metaobject;
- ... call `CHANGE-CLASS` to change the class of any class metaobject or to turn a non-class object into a class metaobject.

Since metaobject classes may not be redefined, no behavior is specified for the result of calls to `UPDATE-INSTANCE-FOR-REDEFINED-CLASS` on class metaobjects. Since the class of class metaobjects may not be changed, no behavior is specified for the result of calls to `UPDATE-INSTANCE-FOR-DIFFERENT-CLASS` on class metaobjects.

During initialization or reinitialization, each initialization argument is checked for errors and then associated with the class metaobject. The value can then be accessed by calling the appropriate accessor as shown in Table 29.2, “Initialization arguments and accessors for class metaobjects”.

This section begins with a description of the error checking and processing of each initialization argument. This is followed by a table showing the generic functions that can be used to access the stored initialization arguments. Initialization behavior specific to the different specified class metaobject classes comes next. The section ends with a set of restrictions on portable methods affecting class metaobject initialization and reinitialization.

In these descriptions, the phrase “this argument defaults to `value`” means that when that initialization argument is not supplied, initialization or reinitialization is performed as if `value` had been supplied. For some initialization arguments this could be done by the use of default initialization arguments, but whether it is done this way is not specified. Implementations are free to define default initialization arguments for specified class metaobject classes. Portable programs are free to define default initialization arguments for portable subclasses of the class `CLASS`.

Unless there is a specific note to the contrary, then during reinitialization, if an initialization argument is not supplied, the previously stored value is left unchanged.

- The `:DIRECT-DEFAULT-INITARGS` argument is a list of canonicalized default initialization arguments.

  An `ERROR` is `SIGNAL`ed if this value is not a proper list, or if any element of the list is not a canonicalized default initialization argument.

  If the class metaobject is being initialized, this argument defaults to the empty list.

- The `:DIRECT-SLOTS` argument is a list of canonicalized slot specifications.

  An `ERROR` is `SIGNAL`ed if this value is not a proper list or if any element of the list is not a canonicalized slot specification.

  After error checking, this value is converted to a list of direct slot definition metaobjects before it is associated with the class metaobject. Conversion of each canonicalized slot specification to a direct slot definition metaobject is a two-step process. First, the generic function `CLOS:DIRECT-SLOT-DEFINITION-CLASS` is called with the class metaobject and the canonicalized slot specification to determine the class of the new direct slot definition metaobject; this permits both the class metaobject and the canonicalized slot specification to control the resulting direct slot definition metaobject class. Second, `MAKE-INSTANCE` is applied to the direct slot definition metaobject class and the canonicalized slot specification. This conversion could be implemented as shown in the following code:

      (DEFUN convert-to-direct-slot-definition (class canonicalized-slot)
        (APPLY #'MAKE-INSTANCE
               (APPLY #'CLOS:DIRECT-SLOT-DEFINITION-CLASS
                      class canonicalized-slot)
               canonicalized-slot))

  If the class metaobject is being initialized, this argument defaults to the empty list.

  Once the direct slot definition metaobjects have been created, the specified reader and writer methods are created. The generic functions `CLOS:READER-METHOD-CLASS` and `CLOS:WRITER-METHOD-CLASS` are called to determine the classes of the method metaobjects created.

- The `:DIRECT-SUPERCLASSES` argument is a list of class metaobjects. Classes which do not support multiple inheritance signal an error if the list contains more than one element.

  An `ERROR` is `SIGNAL`ed if this value is not a proper list or if `CLOS:VALIDATE-SUPERCLASS` applied to `class` and any element of this list returns false.

  When the class metaobject is being initialized, and this argument is either not supplied or is the empty list, this argument defaults as follows: if the class is an instance of `STANDARD-CLASS` or one of its subclasses the default value is a list of the class `STANDARD-OBJECT`; if the class is an instance of `CLOS:FUNCALLABLE-STANDARD-CLASS` or one of its subclasses the default value is a list of the class `CLOS:FUNCALLABLE-STANDARD-OBJECT`.

  ### Implementation dependent: only in CLISP

  If the class is an instance of `STRUCTURE-CLASS` or one of its subclasses the default value is a list of the class `STRUCTURE-OBJECT`

  After any defaulting of the value, the generic function `CLOS:ADD-DIRECT-SUBCLASS` is called once for each element of the list.

  When the class metaobject is being reinitialized and this argument is supplied, the generic function `CLOS:REMOVE-DIRECT-SUBCLASS` is called once for each class metaobject in the previously stored value but not in the new value; the generic function `CLOS:ADD-DIRECT-SUBCLASS` is called once for each class metaobject in the new value but not in the previously stored value.

- The `:DOCUMENTATION` argument is a `STRING` or `NIL`. An `ERROR` is `SIGNAL`ed if it is not. This argument default to `NIL` during initialization.

- The `:NAME` argument is an object.

  If the class is being initialized, this argument defaults to `NIL`.

After the processing and defaulting of initialization arguments described above, the value of each initialization argument is associated with the class metaobject. These values can then be accessed by calling the corresponding generic function. The correspondences are as follows:

Table 29.2. Initialization arguments and accessors for class metaobjects

Initialization Argument | Generic Function
--- | ---
`:DIRECT-DEFAULT-INITARGS` | `CLOS:CLASS-DIRECT-DEFAULT-INITARGS`
`:DIRECT-SLOTS` | `CLOS:CLASS-DIRECT-SLOTS`
`:DIRECT-SUPERCLASSES` | `CLOS:CLASS-DIRECT-SUPERCLASSES`
`:DOCUMENTATION` | `DOCUMENTATION`
`:NAME` | `CLASS-NAME`

Instances of the class `STANDARD-CLASS` support multiple inheritance and reinitialization. Instances of the class `CLOS:FUNCALLABLE-STANDARD-CLASS` support multiple inheritance and reinitialization. For `CLOS:FORWARD-REFERENCED-CLASS`es, all of the initialization arguments default to `NIL`.

### Implementation dependent: only in CLISP

Instances of the class `STRUCTURE-CLASS` do not support multiple inheritance and reinitialization.

Since built-in classes cannot be created or reinitialized by the user, an `ERROR` is `SIGNAL`ed if `INITIALIZE-INSTANCE` or `REINITIALIZE-INSTANCE` are called to initialize or reinitialize a derived instance of the class `BUILT-IN-CLASS`.

##### 29.3.5.1.1. Methods

It is not specified which methods provide the initialization and reinitialization behavior described above. Instead, the information needed to allow portable programs to specialize this behavior is presented as a set of restrictions on the methods a portable program can define. The model is that portable initialization methods have access to the class metaobject when either all or none of the specified initialization has taken effect.

These restrictions govern the methods that a portable program can define on the generic functions `INITIALIZE-INSTANCE`, `REINITIALIZE-INSTANCE`, and `SHARED-INITIALIZE`. These restrictions apply only to methods on these generic functions for which the first specializer is a subclass of the class `CLASS`. Other portable methods on these generic functions are not affected by these restrictions.

- Portable programs must not define methods on `SHARED-INITIALIZE`.

- For `INITIALIZE-INSTANCE` and `REINITIALIZE-INSTANCE`:

  - Portable programs must not define primary methods.
  - Portable programs may define around-methods, but these must be extending, not overriding methods.
  - Portable before-methods must assume that when they are run, none of the initialization behavior described above has been completed.
  - Portable after-methods must assume that when they are run, all of the initialization behavior described above has been completed.

The results are undefined if any of these restrictions are violated.

##### 29.3.5.1.2. Initialization of Anonymous Classes

class metaobjects created with `MAKE-INSTANCE` are usually anonymous ; that is, they have no proper name. An anonymous class metaobject can be given a proper name using `(`SETF` `FIND-CLASS`)` and `(`SETF` `CLASS-NAME`)`.

When a class metaobject is created with `MAKE-INSTANCE`, it is initialized in the usual way. The initialization arguments passed to `MAKE-INSTANCE` are use to establish the definition of the class. Each initialization argument is checked for errors and associated with the class metaobject. The initialization arguments correspond roughly to the arguments accepted by the `DEFCLASS` macro, and more closely to the arguments accepted by the `CLOS:ENSURE-CLASS` function.

Some class metaobject classes allow their instances to be redefined. When permissible, this is done by calling `REINITIALIZE-INSTANCE`. This is discussed in the next section.

An example of creating an anonymous class directly using `MAKE-INSTANCE` follows:

    (flet ((zero () 0)
           (propellor () *propellor*))
      (make-instance 'standard-class
        :name '(my-class foo)
        :direct-superclasses (list (find-class 'plane)
                                   another-anonymous-class)
        :direct-slots `((:name x
                         :initform 0
                         :initfunction ,#'zero
                         :initargs (:x)
                         :readers (position-x)
                         :writers ((setf position-x)))
                        (:name y
                         :initform 0
                         :initfunction ,#'zero
                         :initargs (:y)
                         :readers (position-y)
                         :writers ((setf position-y))))
        :direct-default-initargs `((:engine *propellor* ,#'propellor))))

#### 29.3.5.2. Reinitialization of class metaobjects

Some class metaobject classes allow their instances to be reinitialized. This is done by calling `REINITIALIZE-INSTANCE`. The initialization arguments have the same interpretation as in class initialization.

If the class metaobject was finalized before the call to `REINITIALIZE-INSTANCE`, `CLOS:FINALIZE-INHERITANCE` will be called again once all the initialization arguments have been processed and associated with the class metaobject. In addition, once finalization is complete, any dependents of the class metaobject will be updated by calling `CLOS:UPDATE-DEPENDENT`.

### 29.3.6. Customization

#### 29.3.6.1. Generic Function `(SETF CLASS-NAME)`

Syntax
  `(`(SETF CLASS-NAME)` `new-name` `class`)`
Arguments
  `class`
    a class metaobject.
  `new-name`
    any Lisp object.
Value
  The `new-name` argument.
Purpose

  This function changes the name of `class` to `new-name`. This value is usually a symbol, or `NIL` if the class has no name.

  This function works by calling `REINITIALIZE-INSTANCE` with `class` as its first argument, the symbol `:NAME` as its second argument and `new-name` as its third argument.

#### 29.3.6.2. Generic Function `CLOS:ENSURE-CLASS`

Syntax
  `(`CLOS:ENSURE-CLASS` `name` `&KEY` `&ALLOW-OTHER-KEYS`)`
Arguments
  `name`
    a `SYMBOL`.
  keyword arguments
    Some of the keyword arguments accepted by this function are actually processed by `CLOS:ENSURE-CLASS-USING-CLASS`, others are processed during initialization of the class metaobject (as described in Section 29.3.5.1, “Initialization of class metaobjects”).
Value
  a class metaobject.
Purpose

  This function is called to define or redefine a class with the specified name, and can be called by the user or the implementation. It is the functional equivalent of `DEFCLASS`, and is called by the expansion of the `DEFCLASS` macro.

  The behavior of this function is actually implemented by the generic function `CLOS:ENSURE-CLASS-USING-CLASS`. When `CLOS:ENSURE-CLASS` is called, it immediately calls `CLOS:ENSURE-CLASS-USING-CLASS` and returns that result as its own.

  The first argument to `CLOS:ENSURE-CLASS-USING-CLASS` is computed as follows:

  - If `name` names a class (`FIND-CLASS` returns a class when called with `name`) use that class.
  - Otherwise use `NIL`.

  The second argument is `name`. The remaining arguments are the complete set of keyword arguments received by the `CLOS:ENSURE-CLASS` function.

#### 29.3.6.3. Generic Function `CLOS:ENSURE-CLASS-USING-CLASS`

Syntax
  `(`CLOS:ENSURE-CLASS-USING-CLASS` `class` `name` `&KEY` `:DIRECT-DEFAULT-INITARGS` `:DIRECT-SLOTS` `:DIRECT-SUPERCLASSES` `:NAME` `:METACLASS` `&ALLOW-OTHER-KEYS`)`
Arguments
  `class`
    a class metaobject or `NIL`.
  `name`
    a class name.
  `:METACLASS`
    a class metaobject class or a class metaobject class name. If this argument is not supplied, it defaults to the class named `STANDARD-CLASS`. If a class name is supplied, it is interpreted as the class with that name. If a class name is supplied, but there is no such class, an `ERROR` is `SIGNAL`ed.
  `:DIRECT-SUPERCLASSES`
    a list of which each element is a class metaobject or a class name. An `ERROR` is `SIGNAL`ed if this argument is not a proper list.
  additional keyword arguments
    See Section 29.3.5.1, “Initialization of class metaobjects”
Value
  a class metaobject.
Purpose

  This generic function is called to define or modify the definition of a named class. It is called by the `CLOS:ENSURE-CLASS` function. It can also be called directly.

  The first step performed by this generic function is to compute the set of initialization arguments which will be used to create or reinitialize the named class. The initialization arguments are computed from the full set of keyword arguments received by this generic function as follows:

  - The `:METACLASS` argument is not included in the initialization arguments.

  - If the `:DIRECT-SUPERCLASSES` argument was received by this generic function, it is converted into a list of class metaobjects. This conversion does not affect the structure of the supplied `:DIRECT-SUPERCLASSES` argument. For each element in the `:DIRECT-SUPERCLASSES` argument:

    - If the element is a class metaobject, that class metaobject is used.
    - If the element names a class, that class metaobject is used.

    - Otherwise an instance of the class `CLOS:FORWARD-REFERENCED-CLASS` is created and used. The proper name of the newly created forward referenced class metaobject is set to the element.

      ### Implementation dependent: only in CLISP

      A new `CLOS:FORWARD-REFERENCED-CLASS` instance is only created when one for the given class name does not yet exist; otherwise the existing one is reused. See Implementation of class `CLOS:FORWARD-REFERENCED-CLASS` in CLISP.

  - All other keyword arguments are included directly in the initialization arguments.

  If the `class` argument is `NIL`, a new class metaobject is created by calling the `MAKE-INSTANCE` generic function with the value of the `:METACLASS` argument as its first argument, and the previously computed initialization arguments. The proper name of the newly created class metaobject is set to `name`. The newly created class metaobject is returned.

  If the `class` argument is a `CLOS:FORWARD-REFERENCED-CLASS`, `CHANGE-CLASS` is called to change its class to the value specified by the `:METACLASS` argument. The class metaobject is then reinitialized with the previously initialization arguments. (This is a documented violation of the general constraint that `CHANGE-CLASS` may not be used with class metaobjects.)

  ### Implementation dependent: only in CLISP

  The `class` argument cannot be a `CLOS:FORWARD-REFERENCED-CLASS`. See Implementation of class `CLOS:FORWARD-REFERENCED-CLASS` in CLISP.

  If the class of the `class` argument is not the same as the class specified by the `:METACLASS` argument, an `ERROR` is `SIGNAL`ed.

  Otherwise, the class metaobject `class` is redefined by calling the `REINITIALIZE-INSTANCE` generic function with `class` and the initialization arguments. The `class` argument is then returned.

Methods

`(`CLOS:ENSURE-CLASS-USING-CLASS` (`class` `CLASS`) `name` `&KEY` `:METACLASS` `:DIRECT-SUPERCLASSES` `&ALLOW-OTHER-KEYS`)`

  This method implements the behavior of the generic function in the case where the `class` argument is a class.

  This method can be overridden.

`(`CLOS:ENSURE-CLASS-USING-CLASS` (`class` `CLOS:FORWARD-REFERENCED-CLASS`) `name` `&KEY` `:METACLASS` `:DIRECT-SUPERCLASSES` `&ALLOW-OTHER-KEYS`)`

  This method implements the behavior of the generic function in the case where the `class` argument is a forward referenced class.

  ### Implementation dependent: only in CLISP

  This method does not exist. See Implementation of class `CLOS:FORWARD-REFERENCED-CLASS` in CLISP. Use the method specialized on `NULL` instead.

`(`CLOS:ENSURE-CLASS-USING-CLASS` (`class` `NULL`) `name` `&KEY` `:METACLASS` `:DIRECT-SUPERCLASSES` `&ALLOW-OTHER-KEYS`)`
  This method implements the behavior of the generic function in the case where the `class` argument is `NIL`.

#### 29.3.6.4. Generic Function `CLOS:FINALIZE-INHERITANCE`

Syntax
  `(`CLOS:FINALIZE-INHERITANCE` `class`)`
Arguments
  `class`
    a class metaobject.
Values
  The values returned by this generic function are unspecified.
Purpose

  This generic function is called to finalize a class metaobject. This is described in Section 29.3.4, “Class Finalization Protocol”

  After `CLOS:FINALIZE-INHERITANCE` returns, the class metaobject is finalized and the result of calling `CLOS:CLASS-FINALIZED-P` on the class metaobject will be true.

Methods

`(`CLOS:FINALIZE-INHERITANCE` (`class` `STANDARD-CLASS`))`
`(`CLOS:FINALIZE-INHERITANCE` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`))`
  No behavior is specified for these methods beyond that which is specified for their respective generic functions.
`(`CLOS:FINALIZE-INHERITANCE` (`class` `CLOS:FORWARD-REFERENCED-CLASS`))`
  This method `SIGNAL`s an `ERROR`.

#### 29.3.6.5. Generic Function `MAKE-INSTANCE`

Syntax
  `(`MAKE-INSTANCE` `class` `&REST` `initargs`)`
Arguments
  `class`
    a class metaobject or a class name.
  `initargs`
    a list of alternating initialization argument names and values.
Value
  A newly allocated and initialized instance of `class`.
Purpose
  The generic function `MAKE-INSTANCE` creates and returns a new instance of the given class. Its behavior and use is described in the [ANSI CL standard].

Methods

`(`MAKE-INSTANCE` (`class` `SYMBOL`) `&REST` `initargs`)`
  This method simply invokes `MAKE-INSTANCE` recursively on the arguments `(`FIND-CLASS` `class`)` and `initargs`.
`(`MAKE-INSTANCE` (`class` `STANDARD-CLASS`) `&REST` `initargs`)`
`(`MAKE-INSTANCE` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `&REST` `initargs`)`
  These methods implement the behavior of `MAKE-INSTANCE` described in the [ANSI CL standard] section 7.1 “Object Creation and Initialization”.

#### 29.3.6.6. Generic Function `ALLOCATE-INSTANCE`

Syntax
  `(`ALLOCATE-INSTANCE` `class` `&REST` `initargs`)`
Arguments
  `class`
    a class metaobject.
  `initargs`
    alternating initialization argument names and values.
Value
  A newly allocated instance of `class`
Purpose

  This generic function is called to create a new, uninitialized instance of a class. The interpretation of the concept of an uninitialized instance depends on the class metaobject class.

  Before allocating the new instance, `CLOS:CLASS-FINALIZED-P` is called to see if `class` has been finalized. If it has not been finalized, `CLOS:FINALIZE-INHERITANCE` is called before the new instance is allocated.

Methods

`(`ALLOCATE-INSTANCE` (`class` `STANDARD-CLASS`) `&REST` `initargs``
  This method allocates storage in the instance for each slot with allocation `:INSTANCE`. These slots are unbound. Slots with any other allocation are ignored by this method (no `ERROR` is `SIGNAL`ed).
`(`ALLOCATE-INSTANCE` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `&REST` `initargs`)`

  This method allocates storage in the instance for each slot with allocation `:INSTANCE`. These slots are unbound. Slots with any other allocation are ignored by this method (no `ERROR` is `SIGNAL`ed).

  The funcallable instance function of the instance is undefined - the results are undefined if the instance is applied to arguments before `CLOS:SET-FUNCALLABLE-INSTANCE-FUNCTION` has been used to set the funcallable instance function.

`(`ALLOCATE-INSTANCE` (`class` `BUILT-IN-CLASS`) `&REST` `initargs`)`
  This method `SIGNAL`s an `ERROR`.

#### 29.3.6.7. Generic Function `CLOS:VALIDATE-SUPERCLASS`

Syntax
  `(`CLOS:VALIDATE-SUPERCLASS` `class` `superclass`)`
Arguments
  `class`
    a class metaobject.
  `superclass`
    a class metaobject.
Value
  `BOOLEAN`.
Purpose

  This generic function is called to determine whether the class `superclass` is suitable for use as a superclass of `class`.

  This generic function can be be called by the implementation or user code. It is called during class metaobject initialization and reinitialization, before the direct superclasses are stored. If this generic function returns false, the initialization or reinitialization will signal an error.

Methods

`(`CLOS:VALIDATE-SUPERCLASS` (`class` `CLASS`) (`superclass` `CLASS`))`

  This method returns true in three situations:

  1. If the `superclass` argument is the class named `T`,
  2. if the class of the `class` argument is the same as the class of the `superclass` argument, or
  3. if the class of one of the arguments is `STANDARD-CLASS` and the class of the other is `CLOS:FUNCALLABLE-STANDARD-CLASS`.

  In all other cases, this method returns false.

  This method can be overridden.

  ### Implementation dependent: only in CLISP

  This method also returns true in a fourth situation:

  4. If the class of the `class` argument is a subclass of the class of the `superclass` argument.

Remarks. Defining a method on `CLOS:VALIDATE-SUPERCLASS` requires detailed knowledge of of the internal protocol followed by each of the two class metaobject classes. A method on `CLOS:VALIDATE-SUPERCLASS` which returns true for two different class metaobject classes declares that they are compatible.

#### 29.3.6.8. Generic Function `CLOS:COMPUTE-DIRECT-SLOT-DEFINITION-INITARGS`

### Implementation dependent: only in CLISP

Syntax
  `(`CLOS:COMPUTE-DIRECT-SLOT-DEFINITION-INITARGS` `class` `&REST` `slot-spec`)`
Arguments
  `class`
    a class metaobject.
  `slot-spec`
    a canonicalized slot specification.
Value
  A list of initialization arguments for a direct slot definition metaobject.
Purpose

  This generic function determines the initialization arguments for the direct slot definition for a slot in a class. It is called during initialization of a class. The resulting initialization arguments are passed to `CLOS:DIRECT-SLOT-DEFINITION-CLASS` and then to `MAKE-INSTANCE`.

  This generic function uses the supplied canonicalized slot specification. The value of `:NAME` in the returned initargs is the same as the value of `:NAME` in the supplied `slot-spec` argument.

Methods

`(`CLOS:COMPUTE-DIRECT-SLOT-DEFINITION-INITARGS` (`class` `STANDARD-CLASS`) `&REST` `slot-spec`)`
`(`CLOS:COMPUTE-DIRECT-SLOT-DEFINITION-INITARGS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `&REST` `slot-spec`)`

  This method returns `slot-spec` unmodified.

  This method can be overridden.

#### 29.3.6.9. Generic Function `CLOS:DIRECT-SLOT-DEFINITION-CLASS`

Syntax
  `(`CLOS:DIRECT-SLOT-DEFINITION-CLASS` `class` `&REST` `initargs`)`
Arguments
  `class`
    a class metaobject.
  `initargs`
    a set of initialization arguments and values.
Value
  A subclass of the class `CLOS:DIRECT-SLOT-DEFINITION`.
Purpose

  When a class is initialized, each of the canonicalized slot specifications must be converted to a direct slot definition metaobject. This generic function is called to determine the class of that direct slot definition metaobject.

  The `initargs` argument is simply the canonicalized slot specification for the slot.

Methods

`(`CLOS:DIRECT-SLOT-DEFINITION-CLASS` (`class` `STANDARD-CLASS`) `&REST` `initargs`)`
`(`CLOS:DIRECT-SLOT-DEFINITION-CLASS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `&REST` `initargs`)`

  These methods return the class `CLOS:STANDARD-DIRECT-SLOT-DEFINITION`.

  These methods can be overridden.

#### 29.3.6.10. Generic Function `CLOS:COMPUTE-CLASS-PRECEDENCE-LIST`

Syntax
  `(`CLOS:COMPUTE-CLASS-PRECEDENCE-LIST` `class`)`
Arguments
  `class`
    a class metaobject.
Value
  A list of class metaobjects.
Purpose

  This generic-function is called to determine the class precedence list of a class.

  The result is a list which contains each of `class` and its superclasses once and only once. The first element of the list is `class` and the last element is the class named `T`.

  All methods on this generic function must compute the class precedence list as a function of the ordered direct superclasses of the superclasses of `class`. The results are undefined if the rules used to compute the class precedence list depend on any other factors.

  When a class is finalized, `CLOS:FINALIZE-INHERITANCE` calls this generic function and associates the returned value with the class metaobject. The value can then be accessed by calling `CLOS:CLASS-PRECEDENCE-LIST`.

  The list returned by this function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this function.

Methods

`(`CLOS:COMPUTE-CLASS-PRECEDENCE-LIST` (`class` `CLASS`))`

  This method computes the class precedence list according to the rules described in the [ANSI CL standard] section 4.3.5 “Determining the Class Precedence List”.

  This method `SIGNAL`s an `ERROR` if `class` or any of its superclasses is a `CLOS:FORWARD-REFERENCED-CLASS`.

  This method can be overridden.

#### 29.3.6.11. Generic Function `CLOS:COMPUTE-SLOTS`

Syntax
  `(`CLOS:COMPUTE-SLOTS` `class`)`
Arguments
  `class`
    a class metaobject.
Value
  A set of effective slot definition metaobjects.
Purpose

  This generic function computes a set of effective slot definition metaobjects for the class `class`. The result is a list of effective slot definition metaobjects: one for each slot that will be accessible in instances of `class`.

  This generic function proceeds in 3 steps:

  The first step collects the full set of direct slot definitions from the superclasses of `class`.

  The direct slot definitions are then collected into individual lists, one list for each slot name associated with any of the direct slot definitions. The slot names are compared with `EQL`. Each such list is then sorted into class precedence list order. Direct slot definitions coming from classes earlier in the class precedence list of `class` appear before those coming from classes later in the class precedence list. For each slot name, the generic function `CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION` is called to compute an effective slot definition. The result of `CLOS:COMPUTE-SLOTS` is a list of these effective slot definitions, in unspecified order.

  In the final step, the location for each effective slot definition is set. This is done by specified around-methods; portable methods cannot take over this behavior. For more information on the slot definition locations, see Section 29.10.1, “Instance Structure Protocol”.

  The list returned by this function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this function.

Methods

`(`CLOS:COMPUTE-SLOTS` (`class` `STANDARD-CLASS`))`
`(`CLOS:COMPUTE-SLOTS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`)}`

  These methods implement the specified behavior of the generic function.

  These methods can be overridden.

`(`CLOS:COMPUTE-SLOTS` `:AROUND` (`class` `STANDARD-CLASS`))`
`(`CLOS:COMPUTE-SLOTS` `:AROUND` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`))`
  These methods implement the specified behavior of computing and storing slot locations. These methods cannot be overridden.

#### 29.3.6.12. Generic Function `CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION`

Syntax
  `(`CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION` `class` `name` `direct-slot-definitions`)`
Arguments
  `class`
    a class metaobject.
  `name`
    a slot name.
  `direct-slot-definitions`
    an ordered list of direct slot definition metaobjects. The most specific direct slot definition metaobject appears first in the list.
Value
  An effective slot definition metaobject.
Purpose

  This generic function determines the effective slot definition for a slot in a class. It is called by `CLOS:COMPUTE-SLOTS` once for each slot accessible in instances of `class`.

  This generic function uses the supplied list of direct slot definition metaobjects to compute the inheritance of slot properties for a single slot. The returned effective slot definition represents the result of computing the inheritance. The name of the new effective slot definition is the same as the name of the direct slot definitions supplied.

  The class of the effective slot definition metaobject is determined by calling `CLOS:EFFECTIVE-SLOT-DEFINITION-CLASS`. The effective slot definition is then created by calling `MAKE-INSTANCE`. The initialization arguments passed in this call to `MAKE-INSTANCE` are used to initialize the new effective slot definition metaobject. See Section 29.4, “Slot Definitions” for details.

Methods

`(`CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION` (`class` `STANDARD-CLASS`) `name` `direct-slot-definitions`)`
`(`CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `name` `direct-slot-definitions`)`

  This method implements the inheritance and defaulting of slot options following the rules described in the [ANSI CL standard] section 7.5.3 “Inheritance of Slots and Options”.

  This method can be extended, but the value returned by the extending method must be the value returned by this method.

### Implementation dependent: only in CLISP

The initialization arguments that are passed to `CLOS:EFFECTIVE-SLOT-DEFINITION-CLASS` and `MAKE-INSTANCE` are computed through a call to `CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION-INITARGS`. It is the `CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION-INITARGS` method that implements the inheritance rules.

#### 29.3.6.13. Generic Function `CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION-INITARGS`

### Implementation dependent: only in CLISP

Syntax
  `(`CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION-INITARGS` `class` `direct-slot-definitions`)`
Arguments
  `class`
    a class metaobject.
  `direct-slot-definitions`
    an ordered list of direct slot definition metaobjects. The most specific direct slot definition metaobject appears first in the list.
Value
  A list of initialization arguments for an effective slot definition metaobject.
Purpose

  This generic function determines the initialization arguments for the effective slot definition for a slot in a class. It is called by `CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION`. The resulting initialization arguments are passed to `CLOS:EFFECTIVE-SLOT-DEFINITION-CLASS` and then to `MAKE-INSTANCE`.

  This generic function uses the supplied list of direct slot definition metaobjects to compute the inheritance of slot properties for a single slot. The returned effective slot definition initargs represent the result of computing the inheritance. The value of `:NAME` in the returned initargs is the same as the name of the direct slot definitions supplied.

Methods

`(`CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION-INITARGS` (`class` `STANDARD-CLASS`) `direct-slot-definitions`)`
`(`CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION-INITARGS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `direct-slot-definitions`)`

  This method implements the inheritance and defaulting of slot options following the rules described in the [ANSI CL standard] section 7.5.3 “Inheritance of Slots and Options”.

  This method can be extended.

#### 29.3.6.14. Generic Function `CLOS:EFFECTIVE-SLOT-DEFINITION-CLASS`

Syntax
  `(`CLOS:EFFECTIVE-SLOT-DEFINITION-CLASS` `class` `&REST` `initargs`)`
Arguments
  `class`
    a class metaobject.
  `initargs`
    set of initialization arguments and values.
Value
  A subclass of the class `CLOS:EFFECTIVE-SLOT-DEFINITION-CLASS`.
Purpose
  This generic function is called by `CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION` to determine the class of the resulting effective slot definition metaobject. The `initargs` argument is the set of initialization arguments and values that will be passed to `MAKE-INSTANCE` when the effective slot definition metaobject is created.

Methods

`(`CLOS:EFFECTIVE-SLOT-DEFINITION-CLASS` (`class` `STANDARD-CLASS`) `&REST` `initargs`)`
`(`CLOS:EFFECTIVE-SLOT-DEFINITION-CLASS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `&REST` `initargs`)`

  These methods return the class `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`.

  These methods can be overridden.

#### 29.3.6.15. Generic Function `CLOS:COMPUTE-DEFAULT-INITARGS`

Syntax
  `(`CLOS:COMPUTE-DEFAULT-INITARGS` `class`)`
Arguments
  `class`
    a class metaobject.
Value
  A list of canonicalized default initialization arguments.
Purpose

  This generic-function is called to determine the default initialization arguments for a class.

  The result is a list of canonicalized default initialization arguments, with no duplication among initialization argument names.

  All methods on this generic function must compute the default initialization arguments as a function of only:

  1. the class precedence list of `class`, and
  2. the direct default initialization arguments of each class in that list.

  The results are undefined if the rules used to compute the default initialization arguments depend on any other factors.

  When a class is finalized, `CLOS:FINALIZE-INHERITANCE` calls this generic function and associates the returned value with the class metaobject. The value can then be accessed by calling `CLOS:CLASS-DEFAULT-INITARGS`.

  The list returned by this function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this function.

Methods

`(`CLOS:COMPUTE-DEFAULT-INITARGS` (`class` `STANDARD-CLASS`))`
`(`CLOS:COMPUTE-DEFAULT-INITARGS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`))`

  These methods compute the default initialization arguments according to the rules described in the [ANSI CL standard] section 7.1.3 “Defaulting of Initialization Arguments”.

  These methods signal an error if `class` or any of its superclasses is a `CLOS:FORWARD-REFERENCED-CLASS`.

  These methods can be overridden.

### 29.3.7. Updating Dependencies

#### 29.3.7.1. Generic Function `CLOS:ADD-DIRECT-SUBCLASS`

Syntax
  `(`CLOS:ADD-DIRECT-SUBCLASS` `superclass` `subclass`)`
Arguments
  `superclass`
    a class metaobject.
  `subclass`
    a class metaobject.
Values
  The values returned by this generic function are unspecified.
Purpose

  This generic function is called to maintain a set of backpointers from a class to its direct subclasses. This generic function adds `subclass` to the set of direct subclasses of `superclass`.

  When a class is initialized, this generic function is called once for each direct superclass of the class.

  When a class is reinitialized, this generic function is called once for each added direct superclass of the class. The generic function `CLOS:REMOVE-DIRECT-SUBCLASS` is called once for each deleted direct superclass of the class.

Methods

`(`CLOS:ADD-DIRECT-SUBCLASS` (`superclass` `CLASS`) (`subclass` `CLASS`))`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:REMOVE-DIRECT-SUBCLASS` (`CLASS` `CLASS`)`
  - ``CLOS:CLASS-DIRECT-SUBCLASSES` (`CLASS`)`

#### 29.3.7.2. Generic Function `CLOS:REMOVE-DIRECT-SUBCLASS`

Syntax
  `(`CLOS:REMOVE-DIRECT-SUBCLASS` `superclass` `subclass`)`
Arguments
  `superclass`
    a class metaobject.
  `subclass`
    a class metaobject.
Values
  The values returned by this generic function are unspecified.
Purpose

  This generic function is called to maintain a set of backpointers from a class to its direct subclasses. It removes `subclass` from the set of direct subclasses of `superclass`. No `ERROR` is `SIGNAL`ed if `subclass` is not in this set.

  Whenever a class is reinitialized, this generic function is called once with each deleted direct superclass of the class.

Methods

`(`CLOS:REMOVE-DIRECT-SUBCLASS` (`superclass` `CLASS`) (`subclass` `CLASS`))`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:ADD-DIRECT-SUBCLASS` (`CLASS` `CLASS`)`
  - ``CLOS:CLASS-DIRECT-SUBCLASSES` (`CLASS`)`

## 29.4. Slot Definitions

### 29.4.1. Inheritance Structure of slot definition metaobject Classes

Figure 29.3. Inheritance structure of slot definition metaobject classes

### 29.4.2. Introspection: Readers for slot definition metaobjects

The reader generic functions which simply return information associated with slot definition metaobjects are presented together here in the format described in Section 29.3.3, “Introspection: Readers for class metaobjects”.

Each of the reader generic functions for slot definition metaobjects has the same syntax, accepting one required argument called `slot`, which must be a slot definition metaobject; otherwise, an `ERROR` is `SIGNAL`ed. An `ERROR` is also `SIGNAL`ed if the slot definition metaobject has not been initialized.

These generic functions can be called by the user or the implementation.

For any of these generic functions which returns a list, such lists will not be mutated by the implementation. The results are undefined if a portable program allows such a list to be mutated.

#### 29.4.2.1. Generic Functions

##### 29.4.2.1.1. Generic Function `CLOS:SLOT-DEFINITION-NAME`

###### `(`CLOS:SLOT-DEFINITION-NAME` `slot`)`

Returns the name of `slot`. This value is a symbol that can be used as a variable name. This is the value of the `:NAME` initialization argument that was associated with the slot definition metaobject during initialization.

### Implementation dependent: only in CLISP

The slot name does not need to be usable as a variable name. Slot names like `NIL` or `T` are perfectly valid.

##### 29.4.2.1.2. Generic Function `CLOS:SLOT-DEFINITION-ALLOCATION`

###### `(`CLOS:SLOT-DEFINITION-ALLOCATION` `slot`)`

Returns the allocation of `slot`. This is a symbol. This is the defaulted value of the `:ALLOCATION` initialization argument that was associated with the slot definition metaobject during initialization.

##### 29.4.2.1.3. Generic Function `CLOS:SLOT-DEFINITION-INITFORM`

###### `(`CLOS:SLOT-DEFINITION-INITFORM` `slot`)`

Returns the initialization form of `slot`. This can be any form. This is the defaulted value of the `:INITFORM` initialization argument that was associated with the slot definition metaobject during initialization. When `slot` has no initialization form, the value returned is unspecified (however, `CLOS:SLOT-DEFINITION-INITFUNCTION` is guaranteed to return `NIL`).

##### 29.4.2.1.4. Generic Function `CLOS:SLOT-DEFINITION-INITFUNCTION`

###### `(`CLOS:SLOT-DEFINITION-INITFUNCTION` `slot`)`

Returns the initialization function of `slot`. This value is either a function of no arguments, or `NIL`, indicating that the slot has no initialization function. This is the defaulted value of the `:INITFUNCTION` initialization argument that was associated with the slot definition metaobject during initialization.

##### 29.4.2.1.5. Generic Function `CLOS:SLOT-DEFINITION-TYPE`

###### `(`CLOS:SLOT-DEFINITION-TYPE` `slot`)`

Returns the type of `slot`. This is a type specifier name. This is the defaulted value of the `:TYPE` initialization argument that was associated with the slot definition metaobject during initialization.

##### 29.4.2.1.6. Generic Function `CLOS:SLOT-DEFINITION-INITARGS`

###### `(`CLOS:SLOT-DEFINITION-INITARGS` `slot`)`

Returns the set of initialization argument keywords for `slot`. This is the defaulted value of the `:INITARGS` initialization argument that was associated with the slot definition metaobject during initialization.

#### 29.4.2.2. Methods

The specified methods for the slot definition metaobject readers

`(`CLOS:SLOT-DEFINITION-NAME` (`slot-definition` `CLOS:STANDARD-SLOT-DEFINITION`))`
`(`CLOS:SLOT-DEFINITION-ALLOCATION` (`slot-definition` `CLOS:STANDARD-SLOT-DEFINITION`))`
`(`CLOS:SLOT-DEFINITION-INITFORM` (`slot-definition` `CLOS:STANDARD-SLOT-DEFINITION`))`
`(`CLOS:SLOT-DEFINITION-INITFUNCTION` (`slot-definition` `CLOS:STANDARD-SLOT-DEFINITION`))`
`(`CLOS:SLOT-DEFINITION-TYPE` (`slot-definition` `CLOS:STANDARD-SLOT-DEFINITION`))`
`(`CLOS:SLOT-DEFINITION-INITARGS` (`slot-definition` `CLOS:STANDARD-SLOT-DEFINITION`))`
  No behavior is specified for these methods beyond that which is specified for their respective generic functions.

#### 29.4.2.3. Readers for direct slot definition metaobjects

The following additional reader generic functions are defined for direct slot definition metaobjects.

##### 29.4.2.3.1. Generic Function `CLOS:SLOT-DEFINITION-READERS`

###### `(`CLOS:SLOT-DEFINITION-READERS` `direct-slot-definition`)`

Returns a (possibly empty) set of readers of the `direct-slot-definition`. This value is a list of function names. This is the defaulted value of the `:READERS` initialization argument that was associated with the direct slot definition metaobject during initialization.

##### 29.4.2.3.2. Generic Function `CLOS:SLOT-DEFINITION-WRITERS`

###### `(`CLOS:SLOT-DEFINITION-WRITERS` `direct-slot-definition`)`

Returns a (possibly empty) set of writers of the `direct-slot-definition`. This value is a list of function names. This is the defaulted value of the `:WRITERS` initialization argument that was associated with the direct slot definition metaobject during initialization.

`(`CLOS:SLOT-DEFINITION-READERS` (`direct-slot-definition` `CLOS:STANDARD-DIRECT-SLOT-DEFINITION`))`
`(`CLOS:SLOT-DEFINITION-WRITERS` (`direct-slot-definition` `CLOS:STANDARD-DIRECT-SLOT-DEFINITION`))`
  No behavior is specified for these methods beyond that which is specified for their respective generic functions.

#### 29.4.2.4. Readers for effective slot definition metaobjects

The following reader generic function is defined for effective slot definition metaobjects.

##### 29.4.2.4.1. Generic Function `CLOS:SLOT-DEFINITION-LOCATION`

###### `(`CLOS:SLOT-DEFINITION-LOCATION` `effective-slot-definition`)`

Returns the location of `effective-slot-definition`. The meaning and interpretation of this value is described in Section 29.10.1, “Instance Structure Protocol”.

`(`CLOS:SLOT-DEFINITION-LOCATION` (`effective-slot-definition` `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`))`
  This method returns the value stored by ``CLOS:COMPUTE-SLOTS` `:AROUND` (`STANDARD-CLASS`)` and ``CLOS:COMPUTE-SLOTS` `:AROUND` (`CLOS:FUNCALLABLE-STANDARD-CLASS`)`.

### 29.4.3. Initialization of slot definition metaobjects

A slot definition metaobject can be created by calling `MAKE-INSTANCE`. The initialization arguments establish the definition of the slot definition. A slot definition metaobject cannot be redefined; calling `REINITIALIZE-INSTANCE` `SIGNAL`s an `ERROR`.

Initialization of a slot definition metaobject must be done by calling `MAKE-INSTANCE` and allowing it to call `INITIALIZE-INSTANCE`. Portable programs must not...

- ... call `INITIALIZE-INSTANCE` directly to initialize a slot definition metaobject;
- ... call `SHARED-INITIALIZE` directly to initialize a slot definition metaobject;
- ... call `CHANGE-CLASS` to change the class of any slot definition metaobject or to turn a non-slot-definition object into a slot definition metaobject.

Since metaobject classes may not be redefined, no behavior is specified for the result of calls to `UPDATE-INSTANCE-FOR-REDEFINED-CLASS` on slot definition metaobjects. Since the class of a slot definition metaobject cannot be changed, no behavior is specified for the result of calls to `UPDATE-INSTANCE-FOR-DIFFERENT-CLASS` on slot definition metaobjects.

During initialization, each initialization argument is checked for errors and then associated with the slot definition metaobject. The value can then be accessed by calling the appropriate accessor as shown in Table 29.3, “Initialization arguments and accessors for slot definition metaobjects”.

This section begins with a description of the error checking and processing of each initialization argument. This is followed by a table showing the generic functions that can be used to access the stored initialization arguments.

In these descriptions, the phrase “this argument defaults to `value`” means that when that initialization argument is not supplied, initialization is performed as if `value` had been supplied. For some initialization arguments this could be done by the use of default initialization arguments, but whether it is done this way is not specified. Implementations are free to define default initialization arguments for specified slot definition metaobject classes. Portable programs are free to define default initialization arguments for portable subclasses of the class `CLOS:SLOT-DEFINITION`.

- The `:NAME` argument is a slot name. An `ERROR` is `SIGNAL`ed if this argument is not a symbol which can be used as a variable name. An `ERROR` is `SIGNAL`ed if this argument is not supplied.

  ### Implementation dependent: only in CLISP

  The `:NAME` argument does not need to be usable as a variable name. Slot names like `NIL` or `T` are perfectly valid.

- The `:INITFORM` argument is a form. The `:INITFORM` argument defaults to `NIL`. An `ERROR` is `SIGNAL`ed if the `:INITFORM` argument is supplied, but the `:INITFUNCTION` argument is not supplied.
- The `:INITFUNCTION` argument is a function of zero arguments which, when called, evaluates the `:INITFORM` in the appropriate lexical environment. The `:INITFUNCTION` argument defaults to false. An `ERROR` is `SIGNAL`ed if the `:INITFUNCTION` argument is supplied, but the `:INITFORM` argument is not supplied.
- The `:TYPE` argument is a type specifier name. An `ERROR` is `SIGNAL`ed otherwise. The `:TYPE` argument defaults to the symbol `T`.
- The `:ALLOCATION` argument is a `SYMBOL`. An `ERROR` is `SIGNAL`ed otherwise. The `:ALLOCATION` argument defaults to the symbol `:INSTANCE`.
- The `:INITARGS` argument is a `LIST` of `SYMBOL`s. An `ERROR` is `SIGNAL`ed if this argument is not a proper list, or if any element of this list is not a `SYMBOL`. The `:INITARGS` argument defaults to the empty list.
- The `:READERS` and `:WRITERS` arguments are `LIST`s of function names. An `ERROR` is `SIGNAL`ed if they are not proper lists, or if any element is not a valid function name. They default to the empty list. An `ERROR` is `SIGNAL`ed if either of these arguments is supplied and the metaobject is not a `CLOS:DIRECT-SLOT-DEFINITION`.
- The `:DOCUMENTATION` argument is a `STRING` or `NIL`. An `ERROR` is `SIGNAL`ed if it is not. This argument default to `NIL` during initialization.

After the processing and defaulting of initialization arguments described above, the value of each initialization argument is associated with the slot definition metaobject. These values can then be accessed by calling the corresponding generic function. The correspondences are as follows:

Table 29.3. Initialization arguments and accessors for slot definition metaobjects

Initialization Argument | Generic Function
--- | ---
`:NAME` | `CLOS:SLOT-DEFINITION-NAME`
`:INITFORM` | `CLOS:SLOT-DEFINITION-INITFORM`
`:INITFUNCTION` | `CLOS:SLOT-DEFINITION-INITFUNCTION`
`:TYPE` | `CLOS:SLOT-DEFINITION-TYPE`
`:ALLOCATION` | `CLOS:SLOT-DEFINITION-ALLOCATION`
`:INITARGS` | `CLOS:SLOT-DEFINITION-INITARGS`
`:READERS` | `CLOS:SLOT-DEFINITION-READERS`
`:WRITERS` | `CLOS:SLOT-DEFINITION-WRITERS`
`:DOCUMENTATION` | `DOCUMENTATION`

#### 29.4.3.1. Methods

It is not specified which methods provide the initialization and reinitialization behavior described above. Instead, the information needed to allow portable programs to specialize this behavior is presented as a set of restrictions on the methods a portable program can define. The model is that portable initialization methods have access to the slot definition metaobject when either all or none of the specified initialization has taken effect.

These restrictions govern the methods that a portable program can define on the generic functions `INITIALIZE-INSTANCE`, `REINITIALIZE-INSTANCE`, and `SHARED-INITIALIZE`. These restrictions apply only to methods on these generic functions for which the first specializer is a subclass of the class `CLOS:SLOT-DEFINITION`. Other portable methods on these generic functions are not affected by these restrictions.

- Portable programs must not define methods on `SHARED-INITIALIZE` or `REINITIALIZE-INSTANCE`.

- For `INITIALIZE-INSTANCE`:

  - Portable programs must not define primary methods.
  - Portable programs may define around-methods, but these must be extending, not overriding methods.
  - Portable before-methods must assume that when they are run, none of the initialization behavior described above has been completed.
  - Portable after-methods must assume that when they are run, all of the initialization behavior described above has been completed.

The results are undefined if any of these restrictions are violated.

## 29.5. Generic Functions

### 29.5.1. Inheritance Structure of generic function metaobject Classes

Figure 29.4. Inheritance structure of generic function metaobject classes

### 29.5.2. Introspection: Readers for generic function metaobjects

The reader generic functions which simply return information associated with generic function metaobjects are presented together here in the format described in Section 29.3.3, “Introspection: Readers for class metaobjects”.

Each of the reader generic functions for generic function metaobjects has the same syntax, accepting one required argument called `generic-function`, which must be a generic function metaobject; otherwise, an `ERROR` is `SIGNAL`ed. An `ERROR` is also `SIGNAL`ed if the generic function metaobject has not been initialized.

These generic functions can be called by the user or the implementation.

For any of these generic functions which returns a list, such lists will not be mutated by the implementation. The results are undefined if a portable program allows such a list to be mutated.

#### 29.5.2.1. Generic Function `CLOS:GENERIC-FUNCTION-NAME`

##### `(`CLOS:GENERIC-FUNCTION-NAME` `generic-function`)`

Returns the name of the generic function, or `NIL` if the generic function has no name. This is the defaulted value of the `:NAME` initialization argument that was associated with the generic function metaobject during initialization or reinitialization. (See also `(SETF CLOS:GENERIC-FUNCTION-NAME)`.)

#### 29.5.2.2. Generic Function `CLOS:GENERIC-FUNCTION-METHODS`

##### `(`CLOS:GENERIC-FUNCTION-METHODS` `generic-function`)`

Returns the set of methods currently connected to the generic function. This is a set of method metaobjects. This value is maintained by the generic functions `ADD-METHOD` and `REMOVE-METHOD`.

#### 29.5.2.3. Generic Function `CLOS:GENERIC-FUNCTION-LAMBDA-LIST`

##### `(`CLOS:GENERIC-FUNCTION-LAMBDA-LIST` `generic-function`)`

Returns the lambda list of the generic function. This is the defaulted value of the `:LAMBDA-LIST` initialization argument that was associated with the generic function metaobject during initialization or reinitialization. An `ERROR` is `SIGNAL`ed if the lambda list has yet to be supplied.

#### 29.5.2.4. Generic Function `CLOS:GENERIC-FUNCTION-ARGUMENT-PRECEDENCE-ORDER`

##### `(`CLOS:GENERIC-FUNCTION-ARGUMENT-PRECEDENCE-ORDER` `generic-function`)`

Returns the argument precedence order of the generic function. This value is a list of symbols, a permutation of the required parameters in the lambda list of the generic function. This is the defaulted value of the `:ARGUMENT-PRECEDENCE-ORDER` initialization argument that was associated with the generic function metaobject during initialization or reinitialization.

### Implementation dependent: only in CLISP

An `ERROR` is `SIGNAL`ed if the lambda list has not yet been supplied.

#### 29.5.2.5. Generic Function `CLOS:GENERIC-FUNCTION-DECLARATIONS`

##### `(`CLOS:GENERIC-FUNCTION-DECLARATIONS` `generic-function`)`

Returns a possibly empty list of the “declarations” of the generic function. The elements of this list are declaration specifiers. This list is the defaulted value of the `:DECLARATIONS` initialization argument that was associated with the generic function metaobject during initialization or reinitialization.

#### 29.5.2.6. Generic Function `CLOS:GENERIC-FUNCTION-METHOD-CLASS`

##### `(`CLOS:GENERIC-FUNCTION-METHOD-CLASS` `generic-function`)`

Returns the default method class of the generic function. This class must be a subclass of the class `METHOD`. This is the defaulted value of the `:METHOD-CLASS` initialization argument that was associated with the generic function metaobject during initialization or reinitialization.

#### 29.5.2.7. Generic Function `CLOS:GENERIC-FUNCTION-METHOD-COMBINATION`

##### `(`CLOS:GENERIC-FUNCTION-METHOD-COMBINATION` `generic-function`)`

Returns the method combination of the generic function. This is a method combination metaobject. This is the defaulted value of the `:METHOD-COMBINATION` initialization argument that was associated with the generic function metaobject during initialization or reinitialization.

#### 29.5.2.8. Methods

The specified methods for the generic function metaobject reader generic functions

`(`CLOS:GENERIC-FUNCTION-NAME` (`generic-function` `STANDARD-GENERIC-FUNCTION`))`
`(`CLOS:GENERIC-FUNCTION-LAMBDA-LIST` (`generic-function` `STANDARD-GENERIC-FUNCTION`))`
`(`CLOS:GENERIC-FUNCTION-ARGUMENT-PRECEDENCE-ORDER` (`generic-function` `STANDARD-GENERIC-FUNCTION`))`
`(`CLOS:GENERIC-FUNCTION-DECLARATIONS` (`generic-function` `STANDARD-GENERIC-FUNCTION`))`
`(`CLOS:GENERIC-FUNCTION-METHOD-CLASS` (`generic-function` `STANDARD-GENERIC-FUNCTION`))`
`(`CLOS:GENERIC-FUNCTION-METHOD-COMBINATION` (`generic-function` `STANDARD-GENERIC-FUNCTION`))`
  No behavior is specified for these methods beyond that which is specified for their respective generic functions.
`(`CLOS:GENERIC-FUNCTION-METHODS` (`generic-function` `STANDARD-GENERIC-FUNCTION`))`

  No behavior is specified for this method beyond that which is specified for the generic function.

  The value returned by this method is maintained by ``ADD-METHOD`(`STANDARD-GENERIC-FUNCTION` `STANDARD-METHOD`)` and ``REMOVE-METHOD`(`STANDARD-GENERIC-FUNCTION` `STANDARD-METHOD`)`.

### 29.5.3. Initialization of Generic Functions

#### 29.5.3.1. Macro `DEFGENERIC`

The evaluation or execution of a `DEFGENERIC` form results in a call to the `ENSURE-GENERIC-FUNCTION` function. The arguments received by `ENSURE-GENERIC-FUNCTION` are derived from the `DEFGENERIC` form in a defined way. As with `DEFCLASS` and `DEFMETHOD`, the exact macro-expansion of the `DEFGENERIC` form is not defined, only the relationship between the arguments to the macro and the arguments received by `ENSURE-GENERIC-FUNCTION`.

- The `function-name` argument to `DEFGENERIC` becomes the first argument to `ENSURE-GENERIC-FUNCTION`. This is the only positional argument accepted by `ENSURE-GENERIC-FUNCTION`; all other arguments are keyword arguments.
- The `lambda-list` argument to `DEFGENERIC` becomes the value of the `:LAMBDA-LIST` keyword argument to `ENSURE-GENERIC-FUNCTION`.

- For each of the options `:ARGUMENT-PRECEDENCE-ORDER`, `:DOCUMENTATION`, `:GENERIC-FUNCTION-CLASS` and `:METHOD-CLASS`, the value of the option becomes the value of the keyword argument with the same name. If the option does not appear in the macro form, the keyword argument does not appear in the resulting call to `ENSURE-GENERIC-FUNCTION`.

  ### Implementation dependent: only in CLISP

  If the option does not appear in the macro form, the keyword argument appears in the resulting call to `ENSURE-GENERIC-FUNCTION`, with a default value: the `lambda-list` for `:ARGUMENT-PRECEDENCE-ORDER`, `NIL` for `:DOCUMENTATION`, the class `STANDARD-GENERIC-FUNCTION` for `:GENERIC-FUNCTION-CLASS`, the class `STANDARD-METHOD` for `:METHOD-CLASS`. This is needed to make the generic function reflect the `DEFGENERIC` form.

- For the option `:DECLARE`, the list of “declarations” becomes the value of the `:DECLARATIONS` keyword argument. If the `:DECLARE` option does not appear in the macro form, the `:DECLARATIONS` keyword argument does not appear in the call to `ENSURE-GENERIC-FUNCTION`.

  ### Implementation dependent: only in CLISP

  If the `:DECLARE` option does not appear in the macro form, the `:DECLARATIONS` keyword argument appears in the resulting call to `ENSURE-GENERIC-FUNCTION`, with a default value of `NIL`. This is needed to make the generic function reflect the `DEFGENERIC` form.

- The handling of the `:METHOD-COMBINATION` option is not specified.

  ### Implementation dependent: only in CLISP

  If the `:METHOD-COMBINATION` option does not appear in the macro form, the `:METHOD-COMBINATION` keyword argument still appears in the resulting call to `ENSURE-GENERIC-FUNCTION`, but in a position where it can be overridden by user-defined initargs and default initargs.

- ### Implementation dependent: only in CLISP

  The `:DECLARE` keyword is recognized as equivalent to the `:DECLARATIONS` keyword, for compatibility with `ENSURE-GENERIC-FUNCTION` in [ANSI CL standard]. If both `:DECLARE` and `:DECLARATIONS` keyword arguments are specified, an `ERROR` is `SIGNAL`ed.

  Any other generic function options become the value of keyword arguments with the same name. The value of the keyword argument is the tail of the generic function option. An `ERROR` is `SIGNAL`ed if any generic function option appears more than once in the `DEFGENERIC` form.

  The default initargs of the `generic-function-class` are added at the end of the list of arguments to pass to `ENSURE-GENERIC-FUNCTION`. This is needed to make the generic function reflect the `DEFGENERIC` form.

- ### Implementation dependent: only in CLISP

  User-defined options. Any other options become the value of keyword arguments with the same name. The value of the keyword argument is the tail of the option. An `ERROR` is `SIGNAL`ed if any option appears more than once in the `DEFGENERIC` form.

The result of the call to `ENSURE-GENERIC-FUNCTION` is returned as the result of evaluating or executing the `DEFGENERIC` form.

#### 29.5.3.2. Generic Function Invocation Protocol

Associated with each generic function is its discriminating function. Each time the generic function is called, the discriminating function is called to provide the behavior of the generic function. The discriminating function receives the full set of arguments received by the generic function. It must lookup and execute the appropriate methods, and return the appropriate values.

The discriminating function is computed by the highest layer of the generic function invocation protocol, `CLOS:COMPUTE-DISCRIMINATING-FUNCTION`. Whenever a generic function metaobject is initialized, reinitialized, or a method is added or removed, the discriminating function is recomputed. The new discriminating function is then stored with `CLOS:SET-FUNCALLABLE-INSTANCE-FUNCTION`.

Discriminating functions call `CLOS:COMPUTE-APPLICABLE-METHODS` and `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES` to compute the methods applicable to the generic functions arguments. Applicable methods are combined by `CLOS:COMPUTE-EFFECTIVE-METHOD` to produce an effective method . Provisions are made to allow memoization of the method applicability and effective methods computations. (See the description of `CLOS:COMPUTE-DISCRIMINATING-FUNCTION` for details.)

The body of method definitions are processed by `CLOS:MAKE-METHOD-LAMBDA`. The result of this generic function is a lambda expression which is processed by either `COMPILE` or `COMPILE-FILE` to produce a method function. The arguments received by the method function are controlled by the `CALL-METHOD` forms appearing in the effective methods. By default, method functions accept two arguments: a list of arguments to the generic function, and a list of next methods. The list of next methods corresponds to the next methods argument to `CALL-METHOD`. If `CALL-METHOD` appears with additional arguments, these will be passed to the method functions as well; in these cases, `CLOS:MAKE-METHOD-LAMBDA` must have created the method lambdas to expect additional arguments.

### Implementation dependent: only in CLISP

See The generic function `CLOS:MAKE-METHOD-LAMBDA` is not implemented.

See Method function arguments.

#### 29.5.3.3. Initialization of generic function metaobjects

A generic function metaobject can be created by calling `MAKE-INSTANCE`. The initialization arguments establish the definition of the generic function. A generic function metaobject can be redefined by calling `REINITIALIZE-INSTANCE`. Some classes of generic function metaobject do not support redefinition; in these cases, `REINITIALIZE-INSTANCE` `SIGNAL`s an `ERROR`.

Initialization of a generic function metaobject must be done by calling `MAKE-INSTANCE` and allowing it to call `INITIALIZE-INSTANCE`. Reinitialization of a generic function metaobject must be done by calling `REINITIALIZE-INSTANCE`. Portable programs must not

- ... call `INITIALIZE-INSTANCE` directly to initialize a generic function metaobject;
- ... call `SHARED-INITIALIZE` directly to initialize or reinitialize a generic function metaobject;
- ... call `CHANGE-CLASS` to change the class of any generic function metaobject or to turn a non-generic-function object into a generic function metaobject.

Since metaobject classes may not be redefined, no behavior is specified for the result of calls to `UPDATE-INSTANCE-FOR-REDEFINED-CLASS` on generic function metaobjects. Since the class of a generic function metaobject may not be changed, no behavior is specified for the results of calls to `UPDATE-INSTANCE-FOR-DIFFERENT-CLASS` on generic function metaobjects.

During initialization or reinitialization, each initialization argument is checked for errors and then associated with the generic function metaobject. The value can then be accessed by calling the appropriate accessor as shown in Table 29.4, “Initialization arguments and accessors for generic function metaobjects”.

This section begins with a description of the error checking and processing of each initialization argument. This is followed by a table showing the generic functions that can be used to access the stored initialization arguments. The section ends with a set of restrictions on portable methods affecting generic function metaobject initialization and reinitialization.

In these descriptions, the phrase “this argument defaults to `value`” means that when that initialization argument is not supplied, initialization or reinitialization is performed as if `value` had been supplied. For some initialization arguments this could be done by the use of default initialization arguments, but whether it is done this way is not specified. Implementations are free to define default initialization arguments for specified generic function metaobject classes. Portable programs are free to define default initialization arguments for portable subclasses of the class `GENERIC-FUNCTION`.

Unless there is a specific note to the contrary, then during reinitialization, if an initialization argument is not supplied, the previously stored value is left unchanged.

- The `:ARGUMENT-PRECEDENCE-ORDER` argument is a list of symbols.

  An `ERROR` is `SIGNAL`ed if this argument appears but the `:LAMBDA-LIST` argument does not appear. An `ERROR` is `SIGNAL`ed if this value is not a proper list or if this value is not a permutation of the symbols from the required arguments part of the `:LAMBDA-LIST` initialization argument.

  When the generic function is being initialized or reinitialized, and this argument is not supplied, but the `:LAMBDA-LIST` argument is supplied, this value defaults to the symbols from the required arguments part of the `:LAMBDA-LIST` argument, in the order they appear in that argument. If neither argument is supplied, neither are initialized (see the description of `:LAMBDA-LIST`.)

- The `:DECLARATIONS` argument is a list of declaration specifiers.

  An `ERROR` is `SIGNAL`ed if this value is not a proper list or if each of its elements is not a legal declaration specifier.

  When the generic function is being initialized, and this argument is not supplied, it defaults to the empty list.

- The `:DOCUMENTATION` argument is a `STRING` or `NIL`. An `ERROR` is `SIGNAL`ed if it is not. This argument default to `NIL` during initialization.

- The `:LAMBDA-LIST` argument is a lambda list.

  An `ERROR` is `SIGNAL`ed if this value is not a proper generic function lambda list.

  When the generic function is being initialized, and this argument is not supplied, the generic function's lambda list is not initialized. The lambda list will be initialized later, either when the first method is added to the generic function, or a later reinitialization of the generic function.

- The `:METHOD-COMBINATION` argument is a method combination metaobject.

- The `:METHOD-CLASS` argument is a class metaobject.

  An `ERROR` is `SIGNAL`ed if this value is not a subclass of the class `METHOD`.

  When the generic function is being initialized, and this argument is not supplied, it defaults to the class `STANDARD-METHOD`.

- The `:NAME` argument is an object.

  If the generic function is being initialized, this argument defaults to `NIL`.

After the processing and defaulting of initialization arguments described above, the value of each initialization argument is associated with the generic function metaobject. These values can then be accessed by calling the corresponding generic function. The correspondences are as follows:

Table 29.4. Initialization arguments and accessors for generic function metaobjects

Initialization Argument | Generic Function
--- | ---
`:ARGUMENT-PRECEDENCE-ORDER` | `CLOS:GENERIC-FUNCTION-ARGUMENT-PRECEDENCE-ORDER`
`:DECLARATIONS` | `CLOS:GENERIC-FUNCTION-DECLARATIONS`
`:DOCUMENTATION` | `DOCUMENTATION`
`:LAMBDA-LIST` | `CLOS:GENERIC-FUNCTION-LAMBDA-LIST`
`:METHOD-COMBINATION` | `CLOS:GENERIC-FUNCTION-METHOD-COMBINATION`
`:METHOD-CLASS` | `CLOS:GENERIC-FUNCTION-METHOD-CLASS`
`:NAME` | `CLOS:GENERIC-FUNCTION-NAME`

##### 29.5.3.3.1. Methods

It is not specified which methods provide the initialization and reinitialization behavior described above. Instead, the information needed to allow portable programs to specialize this behavior is presented as a set of restrictions on the methods a portable program can define. The model is that portable initialization methods have access to the generic function metaobject when either all or none of the specified initialization has taken effect.

These restrictions govern the methods that a portable program can define on the generic functions `INITIALIZE-INSTANCE`, `REINITIALIZE-INSTANCE`, and `SHARED-INITIALIZE`. These restrictions apply only to methods on these generic functions for which the first specializer is a subclass of the class `GENERIC-FUNCTION`. Other portable methods on these generic functions are not affected by these restrictions.

- Portable programs must not define methods on `SHARED-INITIALIZE`.

- For `INITIALIZE-INSTANCE` and `REINITIALIZE-INSTANCE`:

  - Portable programs must not define primary methods.
  - Portable programs may define around-methods, but these must be extending, not overriding methods.
  - Portable before-methods must assume that when they are run, none of the initialization behavior described above has been completed.
  - Portable after-methods must assume that when they are run, all of the initialization behavior described above has been completed.

The results are undefined if any of these restrictions are violated.

### 29.5.4. Customization

#### 29.5.4.1. Generic Function `(SETF CLOS:GENERIC-FUNCTION-NAME)`

Syntax
  `(`(SETF CLOS:GENERIC-FUNCTION-NAME)` `new-name` `generic-function`)`
Arguments
  `generic-function`
    a generic function metaobject.
  `new-name`
    a function name or `NIL`.
Value
  The `new-name` argument.
Purpose

  This function changes the name of `generic-function` to `new-name`. This value is usually a function name or `NIL`, if the generic function is to have no name.

  This function works by calling `REINITIALIZE-INSTANCE` with `generic-function` as its first argument, the symbol `:NAME` as its second argument and `new-name` as its third argument.

#### 29.5.4.2. Generic Function `ENSURE-GENERIC-FUNCTION`

Syntax
  `(`ENSURE-GENERIC-FUNCTION` `function-name` `&KEY` `&ALLOW-OTHER-KEYS`)`
Arguments
  `function-name`
    a function name
  keyword arguments
    Some of the keyword arguments accepted by this function are actually processed by `CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS`, others are processed during initialization of the generic function metaobject (as described in Section 29.5.3.3, “Initialization of generic function metaobjects”).
Value
  A generic function metaobject.
Purpose

  This function is called to define a globally named generic function or to specify or modify options and declarations that pertain to a globally named generic function as a whole. It can be called by the user or the implementation.

  It is the functional equivalent of `DEFGENERIC`, and is called by the expansion of the `DEFGENERIC` and `DEFMETHOD` macros.

  The behavior of this function is actually implemented by the generic function `CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS`. When `ENSURE-GENERIC-FUNCTION` is called, it immediately calls `CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS` and returns that result as its own.

  The first argument to `CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS` is computed as follows:

  - If `function-name` names a non-generic function, a macro, or a special form, an `ERROR` is `SIGNAL`ed.
  - If `function-name` names a generic function, that generic function metaobject is used.
  - Otherwise, `NIL` is used.

  The second argument is `function-name`. The remaining arguments are the complete set of keyword arguments received by `ENSURE-GENERIC-FUNCTION`.

#### 29.5.4.3. Generic Function `CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS`

Syntax
  `(`CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS` `generic-function` `function-name` `&KEY` `:ARGUMENT-PRECEDENCE-ORDER` `:DECLARATIONS` `:DOCUMENTATION` `:GENERIC-FUNCTION-CLASS` `:LAMBDA-LIST` `:METHOD-CLASS` `:METHOD-COMBINATION` `:NAME` `&ALLOW-OTHER-KEYS`)`
Arguments
  `generic-function`
    a generic function metaobject or `NIL`.
  `function-name`
    a function name
  `:GENERIC-FUNCTION-CLASS`
    a class metaobject or a class name. If it is not supplied, it defaults to the class named `STANDARD-GENERIC-FUNCTION`. If a class name is supplied, it is interpreted as the class with that name. If a class name is supplied, but there is no such class, an `ERROR` is `SIGNAL`ed.
  additional keyword arguments

    see Section 29.5.3.3, “Initialization of generic function metaobjects”.

    ### Implementation dependent: only in CLISP

    The `:DECLARE` keyword is recognized as equivalent to the `:DECLARATIONS` keyword, for compatibility with `ENSURE-GENERIC-FUNCTION` in [ANSI CL standard].

Value
  A generic function metaobject.
Purpose

  The generic function `CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS` is called to define or modify the definition of a globally named generic function. It is called by the `ENSURE-GENERIC-FUNCTION` function. It can also be called directly.

  The first step performed by this generic function is to compute the set of initialization arguments which will be used to create or reinitialize the globally named generic function. These initialization arguments are computed from the full set of keyword arguments received by this generic function as follows:

  - The `:GENERIC-FUNCTION-CLASS` argument is not included in the initialization arguments.
  - If the `:METHOD-CLASS` argument was received by this generic function, it is converted into a class metaobject. This is done by looking up the class name with `FIND-CLASS`. If there is no such class, an `ERROR` is `SIGNAL`ed.
  - All other keyword arguments are included directly in the initialization arguments.

  If the `generic-function` argument is `NIL`, an instance of the class specified by the `:GENERIC-FUNCTION-CLASS` argument is created by calling `MAKE-INSTANCE` with the previously computed initialization arguments. The function name `function-name` is set to name the generic function. The newly created generic function metaobject is returned.

  If the class of the `generic-function` argument is not the same as the class specified by the `:GENERIC-FUNCTION-CLASS` argument, an `ERROR` is `SIGNAL`ed.

  ### Implementation dependent: only in CLISP

  The description of `ENSURE-GENERIC-FUNCTION` in [ANSI CL standard] specifies that in this case, `CHANGE-CLASS` is called if the class of the `generic-function` argument and the class specified by the `:GENERIC-FUNCTION-CLASS` argument are compatible. Given the description of `ENSURE-GENERIC-FUNCTION`, this also applies to the `CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS` function. CLISP's implementation calls `CHANGE-CLASS` always, and leaves it to the `CHANGE-CLASS` function to signal an error if needed.

  Otherwise the generic function `generic-function` is redefined by calling the `REINITIALIZE-INSTANCE` generic function with `generic-function` and the initialization arguments. The `generic-function` argument is then returned.

Methods

`(`CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS` (`generic-function` `GENERIC-FUNCTION`) `function-name` `&KEY` `:GENERIC-FUNCTION-CLASS` `&ALLOW-OTHER-KEYS`)`

  This method implements the behavior of the generic function in the case where `function-name` names an existing generic function.

  This method can be overridden.

`(`CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS` (`generic-function` `NULL`) `function-name` `&KEY` `:GENERIC-FUNCTION-CLASS` `&ALLOW-OTHER-KEYS`)`
  This method implements the behavior of the generic function in the case where `function-name` names no function, generic function, macro or special form.

#### 29.5.4.4. Generic Function `ADD-METHOD`

Syntax
  `(`ADD-METHOD` `generic-function` `method`)`
Arguments
  `generic-function`
    a generic function metaobject.
  `method`
    a method metaobject.
Value
  The `generic-function` argument.
Purpose

  This generic function associates an unattached method with a generic function.

  An `ERROR` is `SIGNAL`ed if the lambda list of the method is not congruent with the lambda list of the generic function.

  An `ERROR` is `SIGNAL`ed if the method is already associated with some other generic function.

  If the given method agrees with an existing method of the generic function on parameter specializers and qualifiers, the existing method is removed by calling `REMOVE-METHOD` before the new method is added. See the [ANSI CL standard] section 7.6.3 “Agreement on Parameter Specializers and Qualifiers” for a definition of agreement in this context.

  Associating the method with the generic function then proceeds in four steps:

  1. add `method` to the set returned by `CLOS:GENERIC-FUNCTION-METHODS` and arrange for `CLOS:METHOD-GENERIC-FUNCTION` to return `generic-function`;
  2. call `CLOS:ADD-DIRECT-METHOD` for each of the method's specializers;
  3. call `CLOS:COMPUTE-DISCRIMINATING-FUNCTION` and install its result with `CLOS:SET-FUNCALLABLE-INSTANCE-FUNCTION`; and
  4. update the dependents of the generic function.

  The generic function `ADD-METHOD` can be called by the user or the implementation.

Methods

`(`ADD-METHOD` (`generic-function` `STANDARD-GENERIC-FUNCTION`) (`method` `STANDARD-METHOD`))`
  No behavior is specified for this method beyond that which is specified for the generic function.
`(`ADD-METHOD` (`generic-function` `STANDARD-GENERIC-FUNCTION`) (`method` `METHOD`))`
  This method is specified by [ANSI CL standard].

#### 29.5.4.5. Generic Function `REMOVE-METHOD`

Syntax
  `(`REMOVE-METHOD` `generic-function` `method`)`
Arguments
  `generic-function`
    a generic function metaobject.
  `method`
    a method metaobject.
Value
  The `generic-function` argument.
Purpose

  This generic function breaks the association between a generic function and one of its methods.

  No `ERROR` is `SIGNAL`ed if the method is not among the methods of the generic function.

  Breaking the association between the method and the generic function proceeds in four steps:

  1. remove `method` from the set returned by `CLOS:GENERIC-FUNCTION-METHODS` and arrange for `CLOS:METHOD-GENERIC-FUNCTION` to return `NIL`;
  2. call `CLOS:REMOVE-DIRECT-METHOD` for each of the method's specializers;
  3. call `CLOS:COMPUTE-DISCRIMINATING-FUNCTION` and install its result with `CLOS:SET-FUNCALLABLE-INSTANCE-FUNCTION`; and
  4. update the dependents of the generic function.

  The generic function `REMOVE-METHOD` can be called by the user or the implementation.

Methods

`(`REMOVE-METHOD` (`generic-function` `STANDARD-GENERIC-FUNCTION`) (`method` `STANDARD-METHOD`))`
  No behavior is specified for this method beyond that which is specified for the generic function.
`(`REMOVE-METHOD` (`generic-function` `STANDARD-GENERIC-FUNCTION`) (`method` `METHOD`))`
  This method is specified by [ANSI CL standard].

#### 29.5.4.6. Generic Function `CLOS:COMPUTE-APPLICABLE-METHODS`

Syntax
  `(`CLOS:COMPUTE-APPLICABLE-METHODS` `generic-function` `arguments`)`
Arguments
  `generic-function`
    a generic function metaobject.
  `arguments`
    a list of objects.
Value
  A possibly empty list of method metaobjects.
Purpose

  This generic function determines the method applicability of a generic function given a list of required arguments. The returned list of method metaobjects is sorted by precedence order with the most specific method appearing first. If no methods are applicable to the supplied arguments the empty list is returned.

  When a generic function is invoked, the discriminating function must determine the ordered list of methods applicable to the arguments. Depending on the generic function and the arguments, this is done in one of three ways: using a memoized value; calling `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES`; or calling `CLOS:COMPUTE-APPLICABLE-METHODS`. (Refer to the description of `CLOS:COMPUTE-DISCRIMINATING-FUNCTION` for the details of this process.)

  The `arguments` argument is permitted to contain more elements than the generic function accepts required arguments; in these cases the extra arguments will be ignored. An `ERROR` is `SIGNAL`ed if `arguments` contains fewer elements than the generic function accepts required arguments.

  The list returned by this function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this function.

Methods

`(`CLOS:COMPUTE-APPLICABLE-METHODS` (`generic-function` `STANDARD-GENERIC-FUNCTION`) `arguments`)`

  This method `SIGNAL`s an `ERROR` if any method of the generic function has a specializer which is neither a class metaobject nor an `EQL` specializer metaobject.

  Otherwise, this method computes the sorted list of applicable methods according to the rules described in the [ANSI CL standard] section 7.6.6 “Method Selection and Combination”

  This method can be overridden. Because of the consistency requirements between this generic function and `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES`, doing so may require also overriding ``CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES` (`STANDARD-GENERIC-FUNCTION` `T`)`.

Remarks. See also the [ANSI CL standard] function `COMPUTE-APPLICABLE-METHODS`.

#### 29.5.4.7. Generic Function `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES`

Syntax
  `(`CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES` `generic-function` `classes`)`
Arguments
  `generic-function`
    a generic function metaobject.
  `classes`
    a list of class metaobjects.
Values
  1. A possibly empty list of method metaobjects.
  2. `BOOLEAN`
Purpose

  This generic function is called to attempt to determine the method applicability of a generic function given only the classes of the required arguments.

  If it is possible to completely determine the ordered list of applicable methods based only on the supplied classes, this generic function returns that list as its primary value and true as its second value. The returned list of method metaobjects is sorted by precedence order, the most specific method coming first. If no methods are applicable to arguments with the specified classes, the empty list and true are returned.

  If it is not possible to completely determine the ordered list of applicable methods based only on the supplied classes, this generic function returns an unspecified primary value and false as its second value.

  When a generic function is invoked, the discriminating function must determine the ordered list of methods applicable to the arguments. Depending on the generic function and the arguments, this is done in one of three ways: using a memoized value; calling `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES`; or calling `CLOS:COMPUTE-APPLICABLE-METHODS`. (Refer to the description of `CLOS:COMPUTE-DISCRIMINATING-FUNCTION` for the details of this process.)

  The following consistency relationship between `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES` and `CLOS:COMPUTE-APPLICABLE-METHODS` must be maintained: for any given generic function and set of arguments, if `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES` returns a second value of true, the primary value must be equal to the value that would be returned by a corresponding call to `CLOS:COMPUTE-APPLICABLE-METHODS`. The results are undefined if a portable method on either of these generic functions causes this consistency to be violated.

  The list returned by this function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this function.

Methods

`(`CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES` (`generic-function` `STANDARD-GENERIC-FUNCTION`) `classes`)`

  If any method of the generic function has a specializer which is neither a class metaobject nor an `EQL` specializer metaobject, this method `SIGNAL`s an `ERROR`.

  In cases where the generic function has no methods with `EQL` specializers, or has no methods with `EQL` specializers that could be applicable to arguments of the supplied classes, this method returns the ordered list of applicable methods as its first value and true as its second value.

  Otherwise this method returns an unspecified primary value and false as its second value.

  This method can be overridden. Because of the consistency requirements between this generic function and `CLOS:COMPUTE-APPLICABLE-METHODS`, doing so may require also overriding ``CLOS:COMPUTE-APPLICABLE-METHODS` (`STANDARD-GENERIC-FUNCTION` `T`)` .

##### Remarks

This generic function exists to allow user extensions which alter method lookup rules, but which base the new rules only on the classes of the required arguments, to take advantage of the class-based method lookup memoization found in many implementations. (There is of course no requirement for an implementation to provide this optimization.)

Such an extension can be implemented by two methods, one on this generic function and one on `CLOS:COMPUTE-APPLICABLE-METHODS`. Whenever the user extension is in effect, the first method will return a second value of true. This should allow the implementation to absorb these cases into its own memoization scheme.

To get appropriate performance, other kinds of extensions may require methods on `CLOS:COMPUTE-DISCRIMINATING-FUNCTION` which implement their own memoization scheme.

#### 29.5.4.8. Generic Function `CLOS:COMPUTE-EFFECTIVE-METHOD`

Syntax
  `(`CLOS:COMPUTE-EFFECTIVE-METHOD` `generic-function` `method-combination` `methods`)`
Arguments
  `generic-function`
    a generic function metaobject.
  `method-combination`
    a method combination metaobject.
  `methods`
    a list of method metaobjects.
Values
  1. An effective method
  2. A list of effective method options
Purpose

  This generic function is called to determine the effective method from a sorted list of method metaobjects.

  An effective method is a form that describes how the applicable methods are to be combined. Inside of effective method forms are `CALL-METHOD` forms which indicate that a particular method is to be called. The arguments to the `CALL-METHOD` form indicate exactly how the method function of the method should be called. (See `CLOS:MAKE-METHOD-LAMBDA` for more details about method functions.)

  An effective method option has the same interpretation and syntax as either the `:ARGUMENTS` or the `:GENERIC-FUNCTION` option in the long form of `DEFINE-METHOD-COMBINATION`.

  More information about the form and interpretation of effective methods and effective method options can be found under the description of the `DEFINE-METHOD-COMBINATION` macro in the CLOS specification.

  This generic function can be called by the user or the implementation. It is called by discriminating functions whenever a sorted list of applicable methods must be converted to an effective method.

Methods

`(`CLOS:COMPUTE-EFFECTIVE-METHOD` (`generic-function` `STANDARD-GENERIC-FUNCTION`) `method-combination` `methods`)`

  This method computes the effective method according to the rules of the method combination type implemented by `method-combination`.

  This method can be overridden.

### Implementation dependent: only in CLISP

The second return value may contain only one `:ARGUMENTS` option and only one `:GENERIC-FUNCTION` option. When overriding a `CLOS:COMPUTE-EFFECTIVE-METHOD` method, before adding an `:ARGUMENTS` or `:GENERIC-FUNCTION` option, you therefore need to check whether it this option is already present.

#### 29.5.4.9. Function `CLOS:COMPUTE-EFFECTIVE-METHOD-AS-FUNCTION`

### Implementation dependent: only in CLISP

Syntax
  `(`CLOS:COMPUTE-EFFECTIVE-METHOD-AS-FUNCTION` `generic-function` `methods` `arguments`)`
Arguments
  `generic-function`
    a generic function metaobject.
  `methods`
    a list of method metaobjects.
  `arguments`
    a list of arguments.
Value
  The effective method as a function, accepting any set of arguments for which all of the given methods are applicable.
Purpose

  This function is called to determine the effective method from a sorted list of method metaobjects, and convert it to a function. The `arguments` are a set of arguments to which the methods are applicable, and are used solely for error message purposes.

  This function calls `CLOS:COMPUTE-EFFECTIVE-METHOD` using the `generic-function`'s method combination, wraps local macro definitions for `CALL-METHOD` and `MAKE-METHOD` around it, handles the `:ARGUMENTS` and `:GENERIC-FUNCTION` options, and compiles the resulting form to a function.

#### 29.5.4.10. Generic Function `CLOS:MAKE-METHOD-LAMBDA`

Syntax
  `(`CLOS:MAKE-METHOD-LAMBDA` `generic-function` `method` `lambda-expression` `environment`)`
Arguments
  `generic-function`
    a generic function metaobject.
  `method`
    a (possibly uninitialized) method metaobject.
  `lambda-expression`
    a lambda expression.
  `environment`
    the same as the `&ENVIRONMENT` argument to macro expansion functions.
Values
  1. A lambda expression
  2. A list of initialization arguments and values
Purpose

  This generic function is called to produce a lambda expression which can itself be used to produce a method function for a method and generic function with the specified classes. The generic function and method the method function will be used with are not required to be the given ones. Moreover, the method metaobject may be uninitialized.

  Either the function `COMPILE`, the special form `FUNCTION` or the function `COERCE` must be used to convert the lambda expression a method function. The method function itself can be applied to arguments with `APPLY` or `FUNCALL`.

  When a method is actually called by an effective method, its first argument will be a list of the arguments to the generic function. Its remaining arguments will be all but the first argument passed to `CALL-METHOD`. By default, all method functions must accept two arguments: the list of arguments to the generic function and the list of next methods.

  For a given generic function and method class, the applicable methods on `CLOS:MAKE-METHOD-LAMBDA` and `CLOS:COMPUTE-EFFECTIVE-METHOD` must be consistent in the following way: each use of `CALL-METHOD` returned by the method on `CLOS:COMPUTE-EFFECTIVE-METHOD` must have the same number of arguments, and the method lambda returned by the method on `CLOS:MAKE-METHOD-LAMBDA` must accept a corresponding number of arguments.

  Note that the system-supplied implementation of `CALL-NEXT-METHOD` is not required to handle extra arguments to the method function. Users who define additional arguments to the method function must either redefine or forego `CALL-NEXT-METHOD`. (See the example below.)

  When the method metaobject is created with `MAKE-INSTANCE`, the method function must be the value of the `:FUNCTION` initialization argument. The additional initialization arguments, returned as the second value of this generic function, must also be passed in this call to `MAKE-INSTANCE`.

Methods

`(`CLOS:MAKE-METHOD-LAMBDA` (`generic-function` `STANDARD-GENERIC-FUNCTION`) (`method` `STANDARD-METHOD`) `lambda-expression` `environment`)`

  This method returns a method lambda which accepts two arguments, the list of arguments to the generic function, and the list of next methods. What initialization arguments may be returned in the second value are unspecified.

  This method can be overridden.

This example shows how to define a kind of method which, from within the body of the method, has access to the actual method metaobject for the method. This simplified code overrides whatever method combination is specified for the generic function, implementing a simple method combination supporting only primary methods, `CALL-NEXT-METHOD` and `NEXT-METHOD-P`. (In addition, its a simplified version of `CALL-NEXT-METHOD` which does no error checking.)

Notice that the extra lexical function bindings get wrapped around the body before `CALL-NEXT-METHOD` is called. In this way, the user's definition of `CALL-NEXT-METHOD` and `NEXT-METHOD-P` are sure to override the system's definitions.

    (defclass my-generic-function (standard-generic-function)
      ()
      (:default-initargs :method-class (find-class 'my-method)))

    (defclass my-method (standard-method) ())

    (defmethod make-method-lambda ((gf my-generic-function)
                                   (method my-method)
                                   lambda-expression
                                   environment)
      (declare (ignore environment))
      `(lambda (args next-methods this-method)
         (,(call-next-method gf method
             `(lambda ,(cadr lambda-expression)
                (flet ((this-method () this-method)
                       (call-next-method (&REST cnm-args)
                         (funcall (method-function (car next-methods))
                                  (or cnm-args args)
                                  (cdr next-methods)
                                  (car next-methods)))
                       (next-method-p ()
                         (not (null next-methods))))
                  ,@(cddr lambda-expression)))
              environment)
           args next-methods)))

    (defmethod compute-effective-method ((gf my-generic-function)
                                         method-combination
                                         methods)
      `(call-method ,(car methods) ,(cdr methods) ,(car methods)))

### Implementation dependent: only in CLISP

The generic function `CLOS:MAKE-METHOD-LAMBDA` is not implemented. Its specification is misdesigned: it mixes compile time and execution time behaviour. The essential problem is: where could the generic-function argument come from?

- If a `DEFMETHOD` form occurs in a source file, is `CLOS:MAKE-METHOD-LAMBDA` then called at compile time or at load time? If it was called at compile time, there's no possible value for the first argument, since the class of the generic function to which the method will belong is not known until load time. If it was called at load time, it would mean that the method's source code could only be compiled at load time, not earlier - which defeats the purpose of `COMPILE-FILE`
- When a method is removed from a generic function using `REMOVE-METHOD` and then added through `ADD-METHOD` to a different generic function, possibly belonging to a different generic function class, would `CLOS:MAKE-METHOD-LAMBDA` then be called again or not? If no, then `CLOS:MAKE-METHOD-LAMBDA`'s first argument is useless. If yes, then the source code of every method would have to be present at runtime, and its lexical environment as well.

Method function arguments.

- `CALL-METHOD` always expect exactly two arguments: the method and a list of next methods.
- Method functions always expect exactly two arguments: the list of arguments passed to the generic function, and the list of next methods.

#### 29.5.4.11. Generic Function `CLOS:COMPUTE-DISCRIMINATING-FUNCTION`

Syntax
  `(`CLOS:COMPUTE-DISCRIMINATING-FUNCTION` `generic-function`)`
Arguments
  `generic-function`
    a generic function metaobject.
Value
  A function.
Purpose

  This generic function is called to determine the discriminating function for a generic function. When a generic function is called, the installed discriminating function is called with the full set of arguments received by the generic function, and must implement the behavior of calling the generic function: determining the ordered set of applicable methods, determining the effective method, and running the effective method.

  To determine the ordered set of applicable methods, the discriminating function first calls `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES`. If `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES` returns a second value of false, the discriminating function then calls `CLOS:COMPUTE-APPLICABLE-METHODS`.

  When `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES` returns a second value of true, the discriminating function is permitted to memoize the primary value as follows. The discriminating function may reuse the list of applicable methods without calling `CLOS:COMPUTE-APPLICABLE-METHODS-USING-CLASSES` again provided that:

  1. the generic function is being called again with required arguments which are instances of the same classes,
  2. the generic function has not been reinitialized,
  3. no method has been added to or removed from the generic function,
  4. for all the specializers of all the generic function's methods which are classes, their class precedence lists have not changed, and
  5. for any such memoized value, the class precedence list of the class of each of the required arguments has not changed.

  Determination of the effective method is done by calling `CLOS:COMPUTE-EFFECTIVE-METHOD`. When the effective method is run, each method's function is called, and receives as arguments:

  1. a list of the arguments to the generic function,
  2. whatever other arguments are specified in the `CALL-METHOD` form indicating that the method should be called.

  (See `CLOS:MAKE-METHOD-LAMBDA` for more information about how method functions are called.)

  The generic function `CLOS:COMPUTE-DISCRIMINATING-FUNCTION` is called, and its result installed, by `ADD-METHOD`, `REMOVE-METHOD`, `INITIALIZE-INSTANCE` and `REINITIALIZE-INSTANCE`.

Methods

`(`CLOS:COMPUTE-DISCRIMINATING-FUNCTION` (`generic-function` `STANDARD-GENERIC-FUNCTION`))`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method can be overridden.

### Implementation dependent: only in CLISP

Overriding methods can make use of the function `CLOS:COMPUTE-EFFECTIVE-METHOD-AS-FUNCTION`. It is more convenient to call `CLOS:COMPUTE-EFFECTIVE-METHOD-AS-FUNCTION` than `CLOS:COMPUTE-EFFECTIVE-METHOD` because the in the latter case one needs a lot of “glue code” for implementing the local macros `CALL-METHOD` and `MAKE-METHOD`, and this glue code is implementation dependent because it needs

1. to retrieve the declarations list stored in the method-combination object and
2. to handle implementation dependent options that are returned as second value from `CLOS:COMPUTE-EFFECTIVE-METHOD`.

## 29.6. Methods

### 29.6.1. Inheritance Structure of method metaobject Classes

Figure 29.5. Inheritance structure of method metaobject classes

### 29.6.2. Introspection: Readers for method metaobjects

The reader generic functions which simply return information associated with method metaobjects are presented together here in the format described in Section 29.3.3, “Introspection: Readers for class metaobjects”.

Each of these reader generic functions have the same syntax, accepting one required argument called `method`, which must be a method metaobject; otherwise, an `ERROR` is `SIGNAL`ed. An `ERROR` is also `SIGNAL`ed if the method metaobject has not been initialized.

These generic functions can be called by the user or the implementation.

For any of these generic functions which returns a list, such lists will not be mutated by the implementation. The results are undefined if a portable program allows such a list to be mutated.

#### 29.6.2.1. Generic Function `CLOS:METHOD-SPECIALIZERS`

##### `(`CLOS:METHOD-SPECIALIZERS` `method`)`

Returns a list of the specializers of `method`. This value is a list of specializer metaobjects. This is the value of the `:SPECIALIZERS` initialization argument that was associated with the method during initialization.

#### 29.6.2.2. Generic Function `METHOD-QUALIFIERS`

##### `(`METHOD-QUALIFIERS` `method`)`

Returns a (possibly empty) list of the qualifiers of `method`. This value is a list of non-`NIL` atoms. This is the defaulted value of the `:QUALIFIERS` initialization argument that was associated with the method during initialization.

#### 29.6.2.3. Generic Function `CLOS:METHOD-LAMBDA-LIST`

##### `(`CLOS:METHOD-LAMBDA-LIST` `method`)`

Returns the (unspecialized) lambda list of `method`. This value is a Common Lisp lambda list. This is the value of the `:LAMBDA-LIST` initialization argument that was associated with the method during initialization.

#### 29.6.2.4. Generic Function `CLOS:METHOD-GENERIC-FUNCTION`

##### `(`CLOS:METHOD-GENERIC-FUNCTION` `method`)`

Returns the generic function that `method` is currently connected to, or `NIL` if it is not currently connected to any generic function. This value is either a generic function metaobject or `NIL`. When a method is first created it is not connected to any generic function. This connection is maintained by the generic functions `ADD-METHOD` and `REMOVE-METHOD`.

#### 29.6.2.5. Generic Function `CLOS:METHOD-FUNCTION`

##### `(`CLOS:METHOD-FUNCTION` `method`)`

Returns the method function of `method`. This is the value of the `:FUNCTION` initialization argument that was associated with the method during initialization.

#### 29.6.2.6. Methods

The specified methods for the method metaobject readers

`(`CLOS:METHOD-SPECIALIZERS` (`method` `STANDARD-METHOD`))`
`(`METHOD-QUALIFIERS` (`method` `STANDARD-METHOD`))`
`(`CLOS:METHOD-LAMBDA-LIST` (`method` `STANDARD-METHOD`))`
`(`CLOS:METHOD-FUNCTION` (`method` `STANDARD-METHOD`))`
  No behavior is specified for these methods beyond that which is specified for their respective generic functions.
`(`CLOS:METHOD-GENERIC-FUNCTION` (`method` `STANDARD-METHOD`))`

  No behavior is specified for this method beyond that which is specified for the generic function.

  The value returned by this method is maintained by ``ADD-METHOD`(`STANDARD-GENERIC-FUNCTION` `STANDARD-METHOD`)` and ``REMOVE-METHOD`(`STANDARD-GENERIC-FUNCTION` `STANDARD-METHOD`)`.

### 29.6.3. Initialization of Methods

#### 29.6.3.1. Macro `DEFMETHOD`

The evaluation or execution of a `DEFMETHOD` form requires first that the body of the method be converted to a method function. This process is described below. The result of this process is a method function and a set of additional initialization arguments to be used when creating the new method. Given these two values, the evaluation or execution of a `DEFMETHOD` form proceeds in three steps.

The first step ensures the existence of a generic function with the specified name. This is done by calling the function `ENSURE-GENERIC-FUNCTION`. The first argument in this call is the generic function name specified in the `DEFMETHOD` form.

The second step is the creation of the new method metaobject by calling `MAKE-INSTANCE`. The class of the new method metaobject is determined by calling `CLOS:GENERIC-FUNCTION-METHOD-CLASS` on the result of the call to `ENSURE-GENERIC-FUNCTION` from the first step.

The initialization arguments received by the call to `MAKE-INSTANCE` are as follows:

- The value of the `:QUALIFIERS` initialization argument is a list of the qualifiers which appeared in the `DEFMETHOD` form. No special processing is done on these values. The order of the elements of this list is the same as in the `DEFMETHOD` form.
- The value of the `:LAMBDA-LIST` initialization argument is the unspecialized lambda list from the `DEFMETHOD` form.
- The value of the `:SPECIALIZERS` initialization argument is a list of the specializers for the method. For specializers which are classes, the specializer is the class metaobject itself. In the case of `EQL` specializers, it will be an `CLOS:EQL-SPECIALIZER` metaobject obtained by calling `CLOS:INTERN-EQL-SPECIALIZER` on the result of evaluating the `EQL` specializer form in the lexical environment of the `DEFMETHOD` form.
- The value of the `:FUNCTION` initialization argument is the method function.

- The value of the `:DECLARATIONS` initialization argument is a list of the declaration specifiers from the `DEFMETHOD` form. If there are no declarations in the macro form, this initialization argument either does not appear, or appears with a value of the empty list.

  ### Implementation dependent: only in CLISP

  No `:DECLARATIONS` initialization argument is provided, because method initialization does not support a `:DECLARATIONS` argument, and because the method function is already completely provided through the `:FUNCTION` initialization argument.

- The value of the `:DOCUMENTATION` initialization argument is the documentation string from the `DEFMETHOD` form. If there is no documentation string in the macro form this initialization argument either does not appear, or appears with a value of false.
- Any other initialization argument produced in conjunction with the method function are also included.
- The implementation is free to include additional initialization arguments provided these are not symbols accessible in the “COMMON-LISP-USER” package, or exported by any package defined in the [ANSI CL standard].

In the third step, `ADD-METHOD` is called to add the newly created method to the set of methods associated with the generic function metaobject.

The result of the call to `ADD-METHOD` is returned as the result of evaluating or executing the `DEFMETHOD` form.

An example showing a typical `DEFMETHOD` form and a sample expansion is shown in the following example:

An example `DEFMETHOD` form and one possible correct expansion. In the expansion, `method-lambda` is the result of calling `CLOS:MAKE-METHOD-LAMBDA` as described in Section 29.6.3.1.1, “Processing Method Bodies”. The initargs appearing after `:FUNCTION` are assumed to be additional initargs returned from the call to `CLOS:MAKE-METHOD-LAMBDA`.

    (defmethod move :before ((p position) (l (eql 0))
                             &OPTIONAL (visiblyp t)
                             &KEY color)
      (set-to-origin p)
      (when visiblyp (show-move p 0 color)))

    (let ((#:g001 (ensure-generic-function 'move)))
      (add-method #:g001
        (make-instance (generic-function-method-class #:g001)
                       :qualifiers '(:before)
                       :specializers (list (find-class 'position)
                                           (intern-eql-specializer 0))
                       :lambda-list '(p l &OPTIONAL (visiblyp t)
                                          &KEY color)
                       :function (function method-lambda)
                       'additional-initarg-1 't
                       'additional-initarg-2 '39)))

The processing of the method body for this method is shown below.

##### 29.6.3.1.1. Processing Method Bodies

Before a method can be created, the list of forms comprising the method body must be converted to a method function. This conversion is a two step process.

### Note

The body of methods can also appear in the `:METHOD` option of `DEFGENERIC` forms. Initial methods are not considered by any of the protocols specified in this document.

During macro-expansion of the `DEFMETHOD` macro shown in the previous example code similar to this would be run to produce the method lambda and additional initargs. In this example, `environment` is the macroexpansion environment of the `DEFMETHOD` macro form.

    (let ((gf (ensure-generic-function 'move)))
      (make-method-lambda
        gf
        (class-prototype (generic-function-method-class gf))
        '(lambda (p l &OPTIONAL (visiblyp t) &KEY color)
           (set-to-origin p)
           (when visiblyp (show-move p 0 color)))
        environment))

The first step occurs during macro-expansion of the macro form. In this step, the method lambda list, declarations and body are converted to a lambda expression called a method lambda . This conversion is based on information associated with the generic function definition in effect at the time the macro form is expanded.

The generic function definition is obtained by calling `ENSURE-GENERIC-FUNCTION` with a first argument of the generic function name specified in the macro form. The `:LAMBDA-LIST` keyword argument is not passed in this call.

Given the generic function, production of the method lambda proceeds by calling `CLOS:MAKE-METHOD-LAMBDA`. The first argument in this call is the generic function obtained as described above. The second argument is the result of calling `CLOS:CLASS-PROTOTYPE` on the result of calling `CLOS:GENERIC-FUNCTION-METHOD-CLASS` on the generic function. The third argument is a lambda expression formed from the method lambda list, declarations and body. The fourth argument is the macro-expansion environment of the macro form; this is the value of the `&ENVIRONMENT` argument to the `DEFMETHOD` macro.

The generic function `CLOS:MAKE-METHOD-LAMBDA` returns two values. The first is the method lambda itself. The second is a list of initialization arguments and values. These are included in the initialization arguments when the method is created.

In the second step, the method lambda is converted to a function which properly captures the lexical scope of the macro form. This is done by having the method lambda appear in the macro-expansion as the argument of the `FUNCTION` special form. During the subsequent evaluation of the macro-expansion, the result of the `FUNCTION` special form is the method function.

### Implementation dependent: only in CLISP

See The generic function `CLOS:MAKE-METHOD-LAMBDA` is not implemented.

##### 29.6.3.1.2. Initialization of Generic Function and method metaobjects

An example of creating a generic function and a method metaobject, and then adding the method to the generic function is shown below. This example is comparable to the method definition shown above:

    (let* ((gf (make-instance 'standard-generic-function
                              :lambda-list '(p l &OPTIONAL visiblyp &KEY)))
           (method-class (generic-function-method-class gf)))
      (multiple-value-bind (lambda initargs)
           (make-method-lambda
             gf
             (class-prototype method-class)
             '(lambda (p l &OPTIONAL (visiblyp t) &KEY color)
                (set-to-origin p)
                (when visiblyp (show-move p 0 color)))
             nil)
        (add-method gf
                    (apply #'make-instance method-class
                           :function (compile nil lambda)
                           :specializers (list (find-class 'position)
                                               (intern-eql-specializer 0))
                           :qualifiers ()
                           :lambda-list '(p l &OPTIONAL (visiblyp t)
                                              &KEY color)
                           initargs))))

##### 29.6.3.1.3. Efficiency

###### Implementation dependent: only in CLISP and some other implementations

Methods created through `DEFMETHOD` have a faster calling convention than methods created through a portable `MAKE-INSTANCE` invocation.

#### 29.6.3.2. Initialization of method metaobjects

A method metaobject can be created by calling `MAKE-INSTANCE`. The initialization arguments establish the definition of the method. A method metaobject cannot be redefined; calling `REINITIALIZE-INSTANCE` `SIGNAL`s an `ERROR`.

Initialization of a method metaobject must be done by calling `MAKE-INSTANCE` and allowing it to call `INITIALIZE-INSTANCE`. Portable programs must not

- ... call `INITIALIZE-INSTANCE` directly to initialize a method metaobject;
- ... call `SHARED-INITIALIZE` directly to initialize a method metaobject;
- ... call `CHANGE-CLASS` to change the class of any method metaobject or to turn a non-method object into a method metaobject.

Since metaobject classes may not be redefined, no behavior is specified for the result of calls to `UPDATE-INSTANCE-FOR-REDEFINED-CLASS` on method metaobjects. Since the class of a method metaobject cannot be changed, no behavior is specified for the result of calls to `UPDATE-INSTANCE-FOR-DIFFERENT-CLASS` on method metaobjects.

During initialization, each initialization argument is checked for errors and then associated with the method metaobject. The value can then be accessed by calling the appropriate accessor as shown in Table 29.5, “Initialization arguments and accessors for method metaobjects”.

This section begins with a description of the error checking and processing of each initialization argument. This is followed by a table showing the generic functions that can be used to access the stored initialization arguments. The section ends with a set of restrictions on portable methods affecting method metaobject initialization.

In these descriptions, the phrase “this argument defaults to `value`” means that when that initialization argument is not supplied, initialization is performed as if `value` had been supplied. For some initialization arguments this could be done by the use of default initialization arguments, but whether it is done this way is not specified. Implementations are free to define default initialization arguments for specified method metaobject classes. Portable programs are free to define default initialization arguments for portable subclasses of the class `METHOD`.

- The `:QUALIFIERS` argument is a list of method qualifiers. An `ERROR` is `SIGNAL`ed if this value is not a proper list, or if any element of the list is not a non-null atom. This argument defaults to the empty list.
- The `:LAMBDA-LIST` argument is the unspecialized lambda list of the method. An `ERROR` is `SIGNAL`ed if this value is not a proper lambda list. If this value is not supplied, an `ERROR` is `SIGNAL`ed.
- The `:SPECIALIZERS` argument is a list of the specializer metaobjects for the method. An `ERROR` is `SIGNAL`ed if this value is not a proper list, or if the length of the list differs from the number of required arguments in the `:LAMBDA-LIST` argument, or if any element of the list is not a specializer metaobject. If this value is not supplied, an `ERROR` is `SIGNAL`ed.
- The `:FUNCTION` argument is a method function. It must be compatible with the methods on `CLOS:COMPUTE-EFFECTIVE-METHOD` defined for this class of method and generic function with which it will be used. That is, it must accept the same number of arguments as all uses of `CALL-METHOD` that will call it supply. (See `CLOS:COMPUTE-EFFECTIVE-METHOD` and `CLOS:MAKE-METHOD-LAMBDA` for more information.) An `ERROR` is `SIGNAL`ed if this argument is not supplied.
- When the method being initialized is an instance of a subclass of `CLOS:STANDARD-ACCESSOR-METHOD`, the `:SLOT-DEFINITION` initialization argument must be provided. Its value is the direct slot definition metaobject which defines this accessor method. An `ERROR` is `SIGNAL`ed if the value is not an instance of a subclass of `CLOS:DIRECT-SLOT-DEFINITION`.
- The `:DOCUMENTATION` argument is a string or `NIL`. An `ERROR` is `SIGNAL`ed if this value is not a string or `NIL`. This argument defaults to `NIL`.

After the processing and defaulting of initialization arguments described above, the value of each initialization argument is associated with the method metaobject. These values can then be accessed by calling the corresponding generic function. The correspondences are as follows:

Table 29.5. Initialization arguments and accessors for method metaobjects

Initialization Argument | Generic Function
--- | ---
`:QUALIFIERS` | `METHOD-QUALIFIERS`
`:LAMBDA-LIST` | `CLOS:METHOD-LAMBDA-LIST`
`:SPECIALIZERS` | `CLOS:METHOD-SPECIALIZERS`
`:FUNCTION` | `CLOS:METHOD-FUNCTION`
`:SLOT-DEFINITION` | `CLOS:ACCESSOR-METHOD-SLOT-DEFINITION`
`:DOCUMENTATION` | `DOCUMENTATION`

##### 29.6.3.2.1. Methods

It is not specified which methods provide the initialization behavior described above. Instead, the information needed to allow portable programs to specialize this behavior is presented in as a set of restrictions on the methods a portable program can define. The model is that portable initialization methods have access to the method metaobject when either all or none of the specified initialization has taken effect.

These restrictions govern the methods that a portable program can define on the generic functions `INITIALIZE-INSTANCE`, `REINITIALIZE-INSTANCE`, and `SHARED-INITIALIZE`. These restrictions apply only to methods on these generic functions for which the first specializer is a subclass of the class `METHOD`. Other portable methods on these generic functions are not affected by these restrictions.

- Portable programs must not define methods on `SHARED-INITIALIZE` or `REINITIALIZE-INSTANCE`.

- For `INITIALIZE-INSTANCE`:

  - Portable programs must not define primary methods.
  - Portable programs may define around-methods, but these must be extending, not overriding methods.
  - Portable before-methods must assume that when they are run, none of the initialization behavior described above has been completed.
  - Portable after-methods must assume that when they are run, all of the initialization behavior described above has been completed.

The results are undefined if any of these restrictions are violated.

### 29.6.4. Customization

#### 29.6.4.1. Function `CLOS:EXTRACT-LAMBDA-LIST`

Syntax
  `(`CLOS:EXTRACT-LAMBDA-LIST` `specialized-lambda-list`)`
Arguments
  `specialized-lambda-list`
    a specialized lambda list as accepted by `DEFMETHOD`.
Value
  An unspecialized lambda list.
Purpose

  This function takes a specialized lambda list and returns the lambda list with the specializers removed. This is a non-destructive operation. Whether the result shares any structure with the argument is unspecified.

  If the `specialized-lambda-list` argument does not have legal syntax, an `ERROR` is `SIGNAL`ed. This syntax checking does not check the syntax of the actual specializer names, only the syntax of the lambda list and where the specializers appear.

    (CLOS:EXTRACT-LAMBDA-LIST '((p position)))
    ⇒ (P)
    (CLOS:EXTRACT-LAMBDA-LIST '((p position) x y))
    ⇒ (P X Y)
    (CLOS:EXTRACT-LAMBDA-LIST '(a (b (eql x)) c &REST i))
    ⇒ (A B C &OPTIONAL I)

#### 29.6.4.2. Function `CLOS:EXTRACT-SPECIALIZER-NAMES`

Syntax
  `(`CLOS:EXTRACT-SPECIALIZER-NAMES` `specialized-lambda-list`)`
Arguments
  `specialized-lambda-list`
    a specialized lambda list as accepted by `DEFMETHOD`.
Value
  A list of specializer names.
Purpose

  This function takes a specialized lambda list and returns its specializer names. This is a non-destructive operation. Whether the result shares structure with the argument is unspecified.

  The list returned by this function will not be mutated by the implementation. The results are undefined if a portable program mutates the list returned by this function.

  The result of this function will be a list with a number of elements equal to the number of required arguments in `specialized-lambda-list`. Specializers are defaulted to the symbol `T`.

  If the `specialized-lambda-list` argument does not have legal syntax, an `ERROR` is `SIGNAL`ed. This syntax checking does not check the syntax of the actual specializer names, only the syntax of the lambda list and where the specializers appear.

    (CLOS:EXTRACT-SPECIALIZER-NAMES '((p position)))
    ⇒ (POSITION)
    (CLOS:EXTRACT-SPECIALIZER-NAMES '((p position) x y))
    ⇒ (POSITION T T)
    (CLOS:EXTRACT-SPECIALIZER-NAMES '(a (b (eql x)) c &REST i))
    ⇒ (T (EQL X) T)

## 29.7. Accessor Methods

### 29.7.1. Introspection

#### 29.7.1.1. Generic Function `CLOS:ACCESSOR-METHOD-SLOT-DEFINITION`

##### `(`CLOS:ACCESSOR-METHOD-SLOT-DEFINITION` `method`)`

This accessor can only be called on accessor methods. It returns the direct slot definition metaobject that defined this method. This is the value of the `:SLOT-DEFINITION` initialization argument associated with the method during initialization.

The specified methods for the accessor method metaobject readers

`(`CLOS:ACCESSOR-METHOD-SLOT-DEFINITION` (`method` `CLOS:STANDARD-ACCESSOR-METHOD`))`
  No behavior is specified for this method beyond that which is specified for the generic function.

### 29.7.2. Customization

#### 29.7.2.1. Generic Function `CLOS:READER-METHOD-CLASS`

Syntax
  `(`CLOS:READER-METHOD-CLASS` `class` `direct-slot-definition` `&REST` `initargs`)`
Arguments
  `class`
    a class metaobject.
  `direct-slot-definition`
    a direct slot definition metaobject.
  `initargs`
    alternating initialization argument names and values.
Value
  a class metaobject.
Purpose

  This generic function is called to determine the class of reader methods created during class initialization and reinitialization. The result must be a subclass of `CLOS:STANDARD-READER-METHOD`.

  The `initargs` argument must be the same as will be passed to `MAKE-INSTANCE` to create the reader method. The `initargs` must include `:SLOT-DEFINITION` with `slot-definition` as its value.

Methods

`(`CLOS:READER-METHOD-CLASS` (`class` `STANDARD-CLASS`) (`direct-slot-definition` `CLOS:STANDARD-DIRECT-SLOT-DEFINITION`) `&REST` `initargs`)`
`(`CLOS:READER-METHOD-CLASS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) (`direct-slot-definition` `CLOS:STANDARD-DIRECT-SLOT-DEFINITION`) `&REST` `initargs`)`

  These methods return the class `CLOS:STANDARD-READER-METHOD`.

  These methods can be overridden.

#### 29.7.2.2. Generic Function `CLOS:WRITER-METHOD-CLASS`

Syntax
  `(`CLOS:WRITER-METHOD-CLASS` `class` `direct-slot` `&REST` `initargs`)`
Arguments
  `class`
    a class metaobject.
  `direct-slot`
    a direct slot definition metaobject.
  `initargs`
    a list of initialization arguments and values.
Value
  a class metaobject.
Purpose

  This generic function is called to determine the class of writer methods created during class initialization and reinitialization. The result must be a subclass of `CLOS:STANDARD-WRITER-METHOD`.

  The `initargs` argument must be the same as will be passed to `MAKE-INSTANCE` to create the reader method. The `initargs` must include `:SLOT-DEFINITION` with `CLOS:SLOT-DEFINITION` as its value.

Methods

`(`CLOS:WRITER-METHOD-CLASS` (`class` `STANDARD-CLASS`) (`direct-slot` `CLOS:STANDARD-DIRECT-SLOT-DEFINITION`) `&REST` `initargs`)`
`(`CLOS:WRITER-METHOD-CLASS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) (`direct-slot` `CLOS:STANDARD-DIRECT-SLOT-DEFINITION`) `&REST` `initargs`)`

  These methods return the class `CLOS:STANDARD-WRITER-METHOD`.

  These methods can be overridden.

## 29.8. Specializers

### 29.8.1. Inheritance Structure of Specializer Metaobject Classes

Figure 29.6. Inheritance structure of specializer metaobject classes

### 29.8.2. Introspection

#### 29.8.2.1. Function `CLOS:EQL-SPECIALIZER-OBJECT`

Syntax
  `(`CLOS:EQL-SPECIALIZER-OBJECT` `eql-specializer`)`
Arguments
  `eql-specializer`
    an `EQL` specializer metaobject.
Value
  an object.
Purpose

  This function returns the object associated with `eql-specializer` during initialization. The value is guaranteed to be `EQL` to the value originally passed to `CLOS:INTERN-EQL-SPECIALIZER`, but it is not necessarily `EQ` to that value.

  This function `SIGNAL`s an `ERROR` if `eql-specializer` is not an `EQL` specializer.

### 29.8.3. Initialization

#### 29.8.3.1. Function `CLOS:INTERN-EQL-SPECIALIZER`

Syntax
  `(`CLOS:INTERN-EQL-SPECIALIZER` `object`)`
Arguments
  `object`
    any Lisp object.
Values
  The `EQL` specializer metaobject for `object`.
Purpose
  This function returns the unique `EQL` specializer metaobject for `object`, creating one if necessary. Two calls to `CLOS:INTERN-EQL-SPECIALIZER` with `EQL` arguments will return the same (i.e., `EQ`) value.

Remarks. The result of calling `CLOS:EQL-SPECIALIZER-OBJECT` on the result of a call to `CLOS:INTERN-EQL-SPECIALIZER` is only guaranteed to be `EQL` to the original `object` argument, not necessarily `EQ`.

### 29.8.4. Updating Dependencies

#### 29.8.4.1. Generic Function `CLOS:SPECIALIZER-DIRECT-METHODS`

Syntax
  `(`CLOS:SPECIALIZER-DIRECT-METHODS` `specializer`)`
Arguments
  `specializer`
    a specializer metaobject.
Value
  A possibly empty list of method metaobjects.
Purpose
  This generic function returns the possibly empty set of those methods, connected to generic functions, which have `specializer` as a specializer. The elements of this set are method metaobjects. This value is maintained by the generic functions `CLOS:ADD-DIRECT-METHOD` and `CLOS:REMOVE-DIRECT-METHOD`.

Methods

`(`CLOS:SPECIALIZER-DIRECT-METHODS` (`specializer` `CLASS`))`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:ADD-DIRECT-METHOD` (`CLASS` `METHOD`)`
  - ``CLOS:REMOVE-DIRECT-METHOD` (`CLASS` `METHOD`)`
  - ``CLOS:SPECIALIZER-DIRECT-GENERIC-FUNCTIONS` (`CLASS`)`
`(`CLOS:SPECIALIZER-DIRECT-METHODS` (`specializer` `CLOS:EQL-SPECIALIZER`))`
  No behavior is specified for this method beyond that which is specified for the generic function.

#### 29.8.4.2. Generic Function `CLOS:SPECIALIZER-DIRECT-GENERIC-FUNCTIONS`

Syntax
  `(`CLOS:SPECIALIZER-DIRECT-GENERIC-FUNCTIONS` `specializer`)`
Arguments
  `specializer`
    a specializer metaobject.
Value
  A possibly empty list of generic function metaobjects.
Purpose
  This generic function returns the possibly empty set of those generic functions which have a method with `specializer` as a specializer. The elements of this set are generic function metaobjects. This value is maintained by the generic functions `CLOS:ADD-DIRECT-METHOD` and `CLOS:REMOVE-DIRECT-METHOD`.

Methods

`(`CLOS:SPECIALIZER-DIRECT-GENERIC-FUNCTIONS` (`specializer` `CLASS`))`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:ADD-DIRECT-METHOD` (`CLASS` `METHOD`)`
  - ``CLOS:REMOVE-DIRECT-METHOD` (`CLASS` `METHOD`)`
  - ``CLOS:SPECIALIZER-DIRECT-METHODS` (`CLASS`)`
`(`CLOS:SPECIALIZER-DIRECT-GENERIC-FUNCTIONS` (`specializer` `CLOS:EQL-SPECIALIZER`))`
  No behavior is specified for this method beyond that which is specified for the generic function.

#### 29.8.4.3. Generic Function `CLOS:ADD-DIRECT-METHOD`

Syntax
  `(`CLOS:ADD-DIRECT-METHOD` `specializer` `method`)`
Arguments
  `specializer`
    a specializer metaobject.
  `method`
    a method metaobject.
Values
  The values returned by this generic function are unspecified.
Purpose

  This generic function is called to maintain a set of backpointers from a specializer to the set of methods specialized to it. If `method` is already in the set, it is not added again (no `ERROR` is `SIGNAL`ed).

  This set can be accessed as a list by calling the generic function `CLOS:SPECIALIZER-DIRECT-METHODS`. Methods are removed from the set by `CLOS:REMOVE-DIRECT-METHOD`.

  The generic function `CLOS:ADD-DIRECT-METHOD` is called by `ADD-METHOD` whenever a method is added to a generic function. It is called once for each of the specializers of the method. Note that in cases where a specializer appears more than once in the specializers of a method, this generic function will be called more than once with the same specializer as argument.

  The results are undefined if the `specializer` argument is not one of the specializers of the `method` argument.

Methods

`(`CLOS:ADD-DIRECT-METHOD` (`specializer` `CLASS`) (`method` `METHOD`))`

  This method implements the behavior of the generic function for class specializers.

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:REMOVE-DIRECT-METHOD` (`CLASS` `METHOD`)`
  - ``CLOS:SPECIALIZER-DIRECT-GENERIC-FUNCTIONS` (`CLASS`)`
  - ``CLOS:SPECIALIZER-DIRECT-METHODS` (`CLASS`)`

`(`CLOS:ADD-DIRECT-METHOD` (`specializer` `CLOS:EQL-SPECIALIZER`) (`method` `METHOD`))`

  This method implements the behavior of the generic function for `EQL` specializers.

  No behavior is specified for this method beyond that which is specified for the generic function.

#### 29.8.4.4. Generic Function `CLOS:REMOVE-DIRECT-METHOD`

Syntax
  `(`CLOS:REMOVE-DIRECT-METHOD` `specializer` `method`)`
Arguments
  `specializer`
    a specializer metaobject.
  `method`
    a method metaobject.
Values
  The values returned by this generic function are unspecified.
Purpose

  This generic function is called to maintain a set of backpointers from a specializer to the set of methods specialized to it. If `method` is in the set it is removed. If it is not, no `ERROR` is `SIGNAL`ed.

  This set can be accessed as a list by calling the generic function `CLOS:SPECIALIZER-DIRECT-METHODS`. Methods are added to the set by `CLOS:ADD-DIRECT-METHOD`.

  The generic function `CLOS:REMOVE-DIRECT-METHOD` is called by `REMOVE-METHOD` whenever a method is removed from a generic function. It is called once for each of the specializers of the method. Note that in cases where a specializer appears more than once in the specializers of a method, this generic function will be called more than once with the same specializer as argument.

  The results are undefined if the `specializer` argument is not one of the specializers of the `method` argument.

Methods

`(`CLOS:REMOVE-DIRECT-METHOD` (`specializer` `CLASS`) (`method` `METHOD`))`

  This method implements the behavior of the generic function for class specializers.

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:ADD-DIRECT-METHOD` (`CLASS` `METHOD`)`
  - ``CLOS:SPECIALIZER-DIRECT-GENERIC-FUNCTIONS` (`CLASS`)`
  - ``CLOS:SPECIALIZER-DIRECT-METHODS` (`CLASS`)`
`(`CLOS:REMOVE-DIRECT-METHOD` (`specializer` `CLOS:EQL-SPECIALIZER`) (`method` `METHOD`))`

  This method implements the behavior of the generic function for `EQL` specializers.

  No behavior is specified for this method beyond that which is specified for the generic function.

## 29.9. Method Combinations

### 29.9.1. Inheritance Structure of method combination metaobject Classes

Figure 29.7. Inheritance structure of method combination metaobject classes

### 29.9.2. Customization

#### 29.9.2.1. Generic Function `CLOS:FIND-METHOD-COMBINATION`

Syntax
  `(`CLOS:FIND-METHOD-COMBINATION` `generic-function` `method-combination-type-name` `method-combination-options`)`
Arguments
  `generic-function`
    a generic function metaobject.
  `method-combination-type-name`
    a symbol which names a type of method combination.
  `method-combination-options`
    a list of arguments to the method combination type.
Value
  A method combination metaobject.
Purpose
  This generic function is called to determine the method combination object used by a generic function.

Remarks. Further details of method combination metaobjects are not specified.

## 29.10. Slot Access

### 29.10.1. Instance Structure Protocol

The instance structure protocol is responsible for implementing the behavior of the slot access functions like `SLOT-VALUE` and `(`SETF` `SLOT-VALUE`)`.

For each CLOS slot access function other than `SLOT-EXISTS-P`, there is a corresponding generic function which actually provides the behavior of the function. When called, the slot access function finds the pertinent effective slot definition metaobject, calls the corresponding generic function and returns its result. The arguments passed on to the generic function include one additional value, the class of the `object` argument, which always immediately precedes the `object` argument.

Table 29.6. The correspondence between slot access function and underlying slot access generic function

Slot Access Function | Corresponding Slot Access Generic Function
--- | ---
`SLOT-VALUE` `object` `slot-name` | `CLOS:SLOT-VALUE-USING-CLASS` `class` `object` `slot`
`(`SETF` `SLOT-VALUE`)` `new-value` `object` `slot-name` | `(SETF CLOS:SLOT-VALUE-USING-CLASS)` `new-value` `class` `object` `slot`
`SLOT-BOUNDP` `object` `slot-name` | `CLOS:SLOT-BOUNDP-USING-CLASS` `class` `object` `slot`
`SLOT-MAKUNBOUND` `object` `slot-name` | `CLOS:SLOT-MAKUNBOUND-USING-CLASS` `class` `object` `slot`

At the lowest level, the instance structure protocol provides only limited mechanisms for portable programs to control the implementation of instances and to directly access the storage associated with instances without going through the indirection of slot access. This is done to allow portable programs to perform certain commonly requested slot access optimizations.

In particular, portable programs can control the implementation of, and obtain direct access to, slots with allocation `:INSTANCE` and type `T`. These are called directly accessible slots .

The relevant specified around-method on `CLOS:COMPUTE-SLOTS` determines the implementation of instances by deciding how each slot in the instance will be stored. For each directly accessible slot, this method allocates a location and associates it with the effective slot definition metaobject. The location can be accessed by calling the `CLOS:SLOT-DEFINITION-LOCATION` generic function. Locations are non-negative integers. For a given class, the locations increase consecutively, in the order that the directly accessible slots appear in the list of effective slots. (Note that here, the next paragraph, and the specification of this around-method are the only places where the value returned by `CLOS:COMPUTE-SLOTS` is described as a list rather than a set.)

Given the location of a directly accessible slot, the value of that slot in an instance can be accessed with the appropriate accessor. For `STANDARD-CLASS`, this accessor is the function `CLOS:STANDARD-INSTANCE-ACCESS`. For `CLOS:FUNCALLABLE-STANDARD-CLASS`, this accessor is the function `CLOS:FUNCALLABLE-STANDARD-INSTANCE-ACCESS`. In each case, the arguments to the accessor are the instance and the slot location, in that order. See the definition of each accessor for additional restrictions on the use of these function.

Portable programs are permitted to affect and rely on the allocation of locations only in the following limited way: By first defining a portable primary method on `CLOS:COMPUTE-SLOTS` which orders the returned value in a predictable way, and then relying on the defined behavior of the specified around-method to assign locations to all directly accessible slots. Portable programs may compile-in calls to low-level accessors which take advantage of the resulting predictable allocation of slot locations.

This example shows the use of this mechanism to implement a new class metaobject class, `ordered-class` and class option `:SLOT-ORDER`. This option provides control over the allocation of slot locations. In this simple example implementation, the `:SLOT-ORDER` option is not inherited by subclasses; it controls only instances of the class itself.

    (defclass ordered-class (standard-class)
      ((slot-order :initform ()
                   :initarg :slot-order
                   :reader class-slot-order)))

    (defmethod compute-slots ((class ordered-class))
      (let ((order (class-slot-order class)))
        (sort (copy-list (call-next-method))
              #'(lambda (a b)
                  (< (position (slot-definition-name a) order)
                     (position (slot-definition-name a) order))))))

Following is the source code the user of this extension would write. Note that because the code above does not implement inheritance of the `:SLOT-ORDER` option, the function `distance` must not be called on instances of subclasses of `point`; it can only be called on instances of `point` itself.

    (defclass point ()
      ((x :initform 0)
       (y :initform 0))
      (:metaclass ordered-class)
      (:slot-order x y))

    (defun distance (point)
      (sqrt (/ (+ (expt (standard-instance-access point 0) 2)
                  (expt (standard-instance-access point 1) 2))
               2.0)))

### Implementation dependent: only in CLISP

You cannot assume that the slot-location values start at 0. In class `point`, for example, `x` and `y` will be at slot locations 1 and 2, not 0 and 1.

In more realistic uses of this mechanism, the calls to the low-level instance structure accessors would not actually appear textually in the source program, but rather would be generated by a meta-level analysis program run during the process of compiling the source program.

### 29.10.2. Funcallable Instances

Instances of classes which are themselves instances of `CLOS:FUNCALLABLE-STANDARD-CLASS` or one of its subclasses are called funcallable instances. Funcallable instances can only be created by ``ALLOCATE-INSTANCE` (`CLOS:FUNCALLABLE-STANDARD-CLASS`)`.

Like standard instances, funcallable instances have slots with the normal behavior. They differ from standard instances in that they can be used as functions as well; that is, they can be passed to `FUNCALL` and `APPLY`, and they can be stored as the definition of a function name. Associated with each funcallable instance is the function which it runs when it is called. This function can be changed with `CLOS:SET-FUNCALLABLE-INSTANCE-FUNCTION`.

The following simple example shows the use of funcallable instances to create a simple, `DEFSTRUCT`-like facility. (Funcallable instances are useful when a program needs to construct and maintain a set of functions and information about those functions. They make it possible to maintain both as the same object rather than two separate objects linked, for example, by hash tables.)

    (defclass constructor ()
      ((name :initarg :name :accessor constructor-name)
       (fields :initarg :fields :accessor constructor-fields))
      (:metaclass funcallable-standard-class))
    ⇒ #>FUNCALLABLE-STANDARD-CLASS CONSTRUCTOR>
    (defmethod initialize-instance :after ((c constructor) &KEY)
      (with-slots (name fields) c
        (set-funcallable-instance-function
          c
          #'(lambda ()
              (let ((new (make-array (1+ (length fields)))))
                (setf (aref new 0) name)
                new)))))
    ⇒ #<STANDARD-METHOD :AFTER (#<FUNCALLABLE-STANDARD-CLASS CONSTRUCTOR>)>
    (setq c1 (make-instance 'constructor :name 'position :fields '(x y)))
    ⇒ #<CONSTRUCTOR #<UNBOUND>>
    (setq p1 (funcall c1))
    ⇒ #(POSITION NIL NIL)

### 29.10.3. Customization

#### 29.10.3.1. Function `CLOS:STANDARD-INSTANCE-ACCESS`

Syntax
  `(`CLOS:STANDARD-INSTANCE-ACCESS` `instance` `location`)`
Arguments
  `instance`
    an object.
  `location`
    a slot location
Value
  an object.
Purpose

  This function is called to provide direct access to a slot in an instance. By usurping the normal slot lookup protocol, this function is intended to provide highly optimized access to the slots associated with an instance.

  The following restrictions apply to the use of this function:

  - The `instance` argument must be a standard instance (it must have been returned by ``ALLOCATE-INSTANCE`(`STANDARD-CLASS`)`).
  - The `instance` argument cannot be an non-updated obsolete instance.
  - The `location` argument must be a location of one of the directly accessible slots of the instance's class.
  - The slot must be bound.

  The results are undefined if any of these restrictions are violated.

### Implementation dependent: only in CLISP

The second and third restrictions do not apply in CLISP. CLISP's implementation supports non-updated obsolete instances and also supports slots with allocation `:CLASS`.

#### 29.10.3.2. Function `CLOS:FUNCALLABLE-STANDARD-INSTANCE-ACCESS`

Syntax
  `(`CLOS:FUNCALLABLE-STANDARD-INSTANCE-ACCESS` `instance` `location`)`
Arguments
  `instance`
    an object.
  `location`
    a slot location
Value
  an object.
Purpose

  This function is called to provide direct access to a slot in an instance. By usurping the normal slot lookup protocol, this function is intended to provide highly optimized access to the slots associated with an instance.

  The following restrictions apply to the use of this function:

  - The `instance` argument must be a funcallable instance (it must have been returned by ``ALLOCATE-INSTANCE` (`CLOS:FUNCALLABLE-STANDARD-CLASS`)`).
  - The `instance` argument cannot be an non-updated obsolete instance.
  - The `location` argument must be a location of one of the directly accessible slots of the instance's class.
  - The slot must be bound.

  The results are undefined if any of these restrictions are violated.

### Implementation dependent: only in CLISP

The second and third restrictions do not apply in CLISP. CLISP's implementation supports non-updated obsolete instances and also supports slots with allocation `:CLASS`.

#### 29.10.3.3. Function `CLOS:SET-FUNCALLABLE-INSTANCE-FUNCTION`

Syntax
  `(`CLOS:SET-FUNCALLABLE-INSTANCE-FUNCTION` `funcallable-instance` `function`)`
Arguments
  `funcallable-instance`
    a funcallable instance (it must have been returned by ``ALLOCATE-INSTANCE` (`CLOS:FUNCALLABLE-STANDARD-CLASS`)`).
  `function`
    A function.
Values
  The values returned by this generic function are unspecified.
Purpose
  This function is called to set or to change the function of a funcallable instance. After `CLOS:SET-FUNCALLABLE-INSTANCE-FUNCTION` is called, any subsequent calls to `funcallable-instance` will run the new function.

#### 29.10.3.4. Generic Function `CLOS:SLOT-VALUE-USING-CLASS`

Syntax
  `(`CLOS:SLOT-VALUE-USING-CLASS` `class` `object` `slot`)`
Arguments
  `class`
    a class metaobject - the class of the `object` argument.
  `object`
    an object.
  `slot`
    an effective slot definition metaobject.
Values
  an object.
Purpose

  This generic function implements the behavior of the `SLOT-VALUE` function. It is called by `SLOT-VALUE` with the class of `object` as its first argument and the pertinent effective slot definition metaobject as its third argument.

  The generic function `CLOS:SLOT-VALUE-USING-CLASS` returns the value contained in the given slot of the given object. If the slot is unbound, `SLOT-UNBOUND` is called.

  The results are undefined if the `class` argument is not the class of the `object` argument, or if the `slot` argument does not appear among the set of effective slots associated with the `class` argument.

Methods

`(`CLOS:SLOT-VALUE-USING-CLASS` (`class` `STANDARD-CLASS`) `object` (`slot` `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`))`
`(`CLOS:SLOT-VALUE-USING-CLASS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `object` (`slot` `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`))`

  These methods implement the full behavior of this generic function for slots with allocation `:INSTANCE` and `:CLASS`. If the supplied slot has an allocation other than `:INSTANCE` or `:CLASS` an `ERROR` is `SIGNAL`ed.

  Overriding these methods is permitted, but may require overriding other methods in the standard implementation of the slot access protocol.

`(`CLOS:SLOT-VALUE-USING-CLASS` (`class` `BUILT-IN-CLASS`) `object` `slot`)`
  This method `SIGNAL`s an `ERROR`.

#### 29.10.3.5. Generic Function `(SETF CLOS:SLOT-VALUE-USING-CLASS)`

Syntax
  `(`(SETF CLOS:SLOT-VALUE-USING-CLASS)` `new-value` `class` `object` `slot`)`
Arguments
  `new-value`
    an object.
  `class`
    a class metaobject - the class of the `object` argument.
  `object`
    an object.
  `slot`
    an effective slot definition metaobject.
Value
  The `new-value` argument.
Purpose

  The generic function `(SETF CLOS:SLOT-VALUE-USING-CLASS)` implements the behavior of the `(`SETF` `SLOT-VALUE`)` function. It is called by `(`SETF` `SLOT-VALUE`)` with the class of `object` as its second argument and the pertinent effective slot definition metaobject as its fourth argument.

  The generic function `(SETF CLOS:SLOT-VALUE-USING-CLASS)` sets the value contained in the given slot of the given object to the given new value; any previous value is lost.

  The results are undefined if the `class` argument is not the class of the `object` argument, or if the `slot` argument does not appear among the set of effective slots associated with the `class` argument.

Methods

`(`(SETF CLOS:SLOT-VALUE-USING-CLASS)` `new-value` (`class` `STANDARD-CLASS`) `object` (`slot` `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`))`
`(`(SETF CLOS:SLOT-VALUE-USING-CLASS)` `new-value` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `object` (`slot` `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`))`

  These methods implement the full behavior of this generic function for slots with allocation `:INSTANCE` and `:CLASS`. If the supplied slot has an allocation other than `:INSTANCE` or `:CLASS` an `ERROR` is `SIGNAL`ed.

  Overriding these methods is permitted, but may require overriding other methods in the standard implementation of the slot access protocol.

`(`(SETF CLOS:SLOT-VALUE-USING-CLASS)` `new-value` (`class` `BUILT-IN-CLASS`) `object` `slot`)`
  This method `SIGNAL`s an `ERROR`.

#### 29.10.3.6. Generic Function `CLOS:SLOT-BOUNDP-USING-CLASS`

Syntax
  `(`CLOS:SLOT-BOUNDP-USING-CLASS` `class` `object` `slot`)`
Arguments
  `class`
    a class metaobject - the class of the `object` argument.
  `object`
    an object.
  `slot`
    an effective slot definition metaobject.
Value
  `BOOLEAN`
Purpose

  This generic function implements the behavior of the `SLOT-BOUNDP` function. It is called by `SLOT-BOUNDP` with the class of `object` as its first argument and the pertinent effective slot definition metaobject as its third argument.

  The generic function `CLOS:SLOT-BOUNDP-USING-CLASS` tests whether a specific slot in an instance is bound.

  The results are undefined if the `class` argument is not the class of the `object` argument, or if the `slot` argument does not appear among the set of effective slots associated with the `class` argument.

Methods

`(`CLOS:SLOT-BOUNDP-USING-CLASS` (`class` `STANDARD-CLASS`) `object` (`slot` `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`))`
`(`CLOS:SLOT-BOUNDP-USING-CLASS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `object` (`slot` `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`))`

  These methods implement the full behavior of this generic function for slots with allocation `:INSTANCE` and `:CLASS`. If the supplied slot has an allocation other than `:INSTANCE` or `:CLASS` an `ERROR` is `SIGNAL`ed.

  Overriding these methods is permitted, but may require overriding other methods in the standard implementation of the slot access protocol.

`(`CLOS:SLOT-BOUNDP-USING-CLASS` (`class` `BUILT-IN-CLASS`) `object` `slot`)`
  This method `SIGNAL`s an `ERROR`.

Remarks. In cases where the class metaobject class does not distinguish unbound slots, true should be returned.

#### 29.10.3.7. Generic Function `CLOS:SLOT-MAKUNBOUND-USING-CLASS`

Syntax
  `(`CLOS:SLOT-MAKUNBOUND-USING-CLASS` `class` `object` `slot`)`
Arguments
  `class`
    a class metaobject - the class of the `object` argument.
  `object`
    an object.
  `slot`
    an effective slot definition metaobject.
Value
  The `object` argument.
Purpose

  This generic function implements the behavior of the `SLOT-MAKUNBOUND` function. It is called by `SLOT-MAKUNBOUND` with the class of `object` as its first argument and the pertinent effective slot definition metaobject as its third argument.

  The generic function `CLOS:SLOT-MAKUNBOUND-USING-CLASS` restores a slot in an object to its unbound state. The interpretation of “restoring a slot to its unbound state” depends on the class metaobject class.

  The results are undefined if the `class` argument is not the class of the `object` argument, or if the `slot` argument does not appear among the set of effective slots associated with the `class` argument.

Methods

`(`CLOS:SLOT-MAKUNBOUND-USING-CLASS` (`class` `STANDARD-CLASS`) `object` (`slot` `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`))`
`(`CLOS:SLOT-MAKUNBOUND-USING-CLASS` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `object` (`slot` `CLOS:STANDARD-EFFECTIVE-SLOT-DEFINITION`))`

  These methods implement the full behavior of this generic function for slots with allocation `:INSTANCE` and `:CLASS`. If the supplied slot has an allocation other than `:INSTANCE` or `:CLASS` an `ERROR` is `SIGNAL`ed.

  Overriding these methods is permitted, but may require overriding other methods in the standard implementation of the slot access protocol.

`(`CLOS:SLOT-MAKUNBOUND-USING-CLASS` (`class` `BUILT-IN-CLASS`) `object` `slot`)`
  This method `SIGNAL`s an `ERROR`.

## 29.11. Dependent Maintenance

It is convenient for portable metaobjects to be able to memoize information about other metaobjects, portable or otherwise. Because class and generic function metaobjects can be reinitialized, and generic function metaobjects can be modified by adding and removing methods, a means must be provided to update this memoized information.

The dependent maintenance protocol supports this by providing a way to register an object which should be notified whenever a class or generic function is modified. An object which has been registered this way is called a dependent of the class or generic function metaobject. The dependents of class and generic function metaobjects are maintained with `CLOS:ADD-DEPENDENT` and `CLOS:REMOVE-DEPENDENT`. The dependents of a class or generic function metaobject can be accessed with `CLOS:MAP-DEPENDENTS`. Dependents are notified about a modification by calling `CLOS:UPDATE-DEPENDENT`. (See the specification of `CLOS:UPDATE-DEPENDENT` for detailed description of the circumstances under which it is called.)

To prevent conflicts between two portable programs, or between portable programs and the implementation, portable code must not register metaobjects themselves as dependents. Instead, portable programs which need to record a metaobject as a dependent, should encapsulate that metaobject in some other kind of object, and record that object as the dependent. The results are undefined if this restriction is violated.

This example shows a general facility for encapsulating metaobjects before recording them as dependents. The facility defines a basic kind of encapsulating object: an updater. Specializations of the basic class can be defined with appropriate special updating behavior. In this way, information about the updating required is associated with each updater rather than with the metaobject being updated.

Updaters are used to encapsulate any metaobject which requires updating when a given class or generic function is modified. The function `record-updater` is called to both create an updater and add it to the dependents of the class or generic function. Methods on the generic function `CLOS:UPDATE-DEPENDENT`, specialized to the specific class of updater do the appropriate update work.

    (defclass updater ()
      ((dependent :initarg :dependent :reader dependent)))

    (defun record-updater (class dependee dependent &REST initargs)
      (let ((updater (apply #'make-instance class :dependent dependent
                                                  initargs)))
        (add-dependent dependee updater)
        updater))

A `flush-cache-updater` simply flushes the cache of the dependent when it is updated.

    (defclass flush-cache-updater (updater) ())

    (defmethod update-dependent (dependee (updater flush-cache-updater) &REST args)
      (declare (ignore args))
      (flush-cache (dependent updater)))

### 29.11.1. Protocol

#### 29.11.1.1. Generic Function `CLOS:UPDATE-DEPENDENT`

Syntax
  `(`CLOS:UPDATE-DEPENDENT` `metaobject` `dependent` `&REST` `initargs`)`
Arguments
  `metaobject`
    a class metaobject or a generic function metaobject - the metaobject being reinitialized or otherwise modified.
  `dependent`
    an object - the dependent being updated.
  `initargs`
    a list of the initialization arguments for the metaobject redefinition.
Values
  The values returned by this generic function are unspecified.
Purpose

  This generic function is called to update a dependent of `metaobject`.

  When a class or a generic function is reinitialized each of its dependents is updated. The `initargs` argument to `CLOS:UPDATE-DEPENDENT` is the set of initialization arguments received by `REINITIALIZE-INSTANCE`.

  When a method is added to a generic function, each of the generic function's dependents is updated. The `initargs` argument is a list of two elements: the symbol `ADD-METHOD`, and the method that was added.

  When a method is removed from a generic function, each of the generic function's dependents is updated. The `initargs` argument is a list of two elements: the symbol `REMOVE-METHOD`, and the method that was removed.

  In each case, `CLOS:MAP-DEPENDENTS` is used to call `CLOS:UPDATE-DEPENDENT` on each of the dependents. So, for example, the update of a generic function's dependents when a method is added could be performed by the following code:

      (CLOS:MAP-DEPENDENTS generic-function
                           #'(lambda (dep)
                               (CLOS:UPDATE-DEPENDENT generic-function
                                                      dep 'add-method new-method)))

Remarks. See Section 29.11, “Dependent Maintenance” for remarks about the use of this facility.

#### 29.11.1.2. Generic Function `CLOS:ADD-DEPENDENT`

Syntax
  `(`CLOS:ADD-DEPENDENT` `metaobject` `dependent`)`
Arguments
  `metaobject`
    a class metaobject or a generic function metaobject.
  `dependent`
    an object.
Values
  The values returned by this generic function are unspecified.
Purpose

  This generic function adds `dependent` to the dependents of `metaobject`. If `dependent` is already in the set of dependents it is not added again (no `ERROR` is `SIGNAL`ed).

  The generic function `CLOS:MAP-DEPENDENTS` can be called to access the set of dependents of a class or generic function. The generic function `CLOS:REMOVE-DEPENDENT` can be called to remove an object from the set of dependents of a class or generic function. The effect of calling `CLOS:ADD-DEPENDENT` or `CLOS:REMOVE-DEPENDENT` while a call to `CLOS:MAP-DEPENDENTS` on the same class or generic function is in progress is unspecified.

  The situations in which `CLOS:ADD-DEPENDENT` is called are not specified.

Methods

`(`CLOS:ADD-DEPENDENT` (`class` `STANDARD-CLASS`) `dependent`)`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:REMOVE-DEPENDENT` (`STANDARD-CLASS` `T`)`
  - ``CLOS:MAP-DEPENDENTS` (`STANDARD-CLASS` `T`)`
`(`CLOS:ADD-DEPENDENT` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `dependent`)`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:REMOVE-DEPENDENT` (`CLOS:FUNCALLABLE-STANDARD-CLASS` `T`)`
  - ``CLOS:MAP-DEPENDENTS` (`CLOS:FUNCALLABLE-STANDARD-CLASS` `T`)`
`(`CLOS:ADD-DEPENDENT` (`generic-function` `STANDARD-GENERIC-FUNCTION`) `dependent`)`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:REMOVE-DEPENDENT` (`STANDARD-GENERIC-FUNCTION` `T`)`
  - ``CLOS:MAP-DEPENDENTS` (`STANDARD-GENERIC-FUNCTION` `T`)`

Remarks. See Section 29.11, “Dependent Maintenance” for remarks about the use of this facility.

#### 29.11.1.3. Generic Function `CLOS:REMOVE-DEPENDENT`

Syntax
  `(`CLOS:REMOVE-DEPENDENT` `metaobject` `dependent`)`
Arguments
  `metaobject`
    a class metaobject or a generic function metaobject.
  `dependent`
    an object.
Values
  The values returned by this generic function are unspecified.
Purpose

  This generic function removes `dependent` from the dependents of `metaobject`. If `dependent` is not one of the dependents of `metaobject`, no `ERROR` is `SIGNAL`ed.

  The generic function `CLOS:MAP-DEPENDENTS` can be called to access the set of dependents of a class or generic function. The generic function `CLOS:ADD-DEPENDENT` can be called to add an object from the set of dependents of a class or generic function. The effect of calling `CLOS:ADD-DEPENDENT` or `CLOS:REMOVE-DEPENDENT` while a call to `CLOS:MAP-DEPENDENTS` on the same class or generic function is in progress is unspecified.

  The situations in which `CLOS:REMOVE-DEPENDENT` is called are not specified.

Methods

`(`CLOS:REMOVE-DEPENDENT` (`class` `STANDARD-CLASS`) `dependent`)`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:ADD-DEPENDENT` (`STANDARD-CLASS` `T`)`
  - ``CLOS:MAP-DEPENDENTS` (`STANDARD-CLASS` `T`)`
`(`CLOS:REMOVE-DEPENDENT` (`class` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `dependent`)`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:ADD-DEPENDENT` (`CLOS:FUNCALLABLE-STANDARD-CLASS` `T`)`
  - ``CLOS:MAP-DEPENDENTS` (`CLOS:FUNCALLABLE-STANDARD-CLASS` `T`)`
`(`CLOS:REMOVE-DEPENDENT` (`class` `STANDARD-GENERIC-FUNCTION`) `dependent`)`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:ADD-DEPENDENT` (`STANDARD-GENERIC-FUNCTION` `T`)`
  - ``CLOS:MAP-DEPENDENTS` (`STANDARD-GENERIC-FUNCTION` `T`)`

Remarks. See Section 29.11, “Dependent Maintenance” for remarks about the use of this facility.

#### 29.11.1.4. Generic Function `CLOS:MAP-DEPENDENTS`

Syntax
  `(`CLOS:MAP-DEPENDENTS` `metaobject` `function`)`
Arguments
  `metaobject`
    a class metaobject or a generic function metaobject.
  `function`
    a function which accepts one argument.
Values
  The values returned by this generic function are unspecified.
Purpose
  This generic function applies `function` to each of the dependents of `metaobject`. The order in which the dependents are processed is not specified, but `function` is applied to each dependent once and only once. If, during the mapping, `CLOS:ADD-DEPENDENT` or `CLOS:REMOVE-DEPENDENT` is called to alter the dependents of `metaobject`, it is not specified whether the newly added or removed dependent will have `function` applied to it.

Methods

`(`CLOS:MAP-DEPENDENTS` (`metaobject` `STANDARD-CLASS`) `function`)`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:ADD-DEPENDENT` (`STANDARD-CLASS` `T`)`
  - ``CLOS:REMOVE-DEPENDENT` (`STANDARD-CLASS` `T`)`
`(`CLOS:MAP-DEPENDENTS` (`metaobject` `CLOS:FUNCALLABLE-STANDARD-CLASS`) `function`)`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:ADD-DEPENDENT` (`CLOS:FUNCALLABLE-STANDARD-CLASS` `T`)`
  - ``CLOS:REMOVE-DEPENDENT` (`CLOS:FUNCALLABLE-STANDARD-CLASS` `T`)`
`(`CLOS:MAP-DEPENDENTS` (`metaobject` `STANDARD-GENERIC-FUNCTION`) `function`)`

  No behavior is specified for this method beyond that which is specified for the generic function.

  This method cannot be overridden unless the following methods are overridden as well:

  - ``CLOS:ADD-DEPENDENT` (`STANDARD-GENERIC-FUNCTION` `T`)`
  - ``CLOS:REMOVE-DEPENDENT` (`STANDARD-GENERIC-FUNCTION` `T`)`

Remarks. See Section 29.11, “Dependent Maintenance” for remarks about the use of this facility.

## 29.12. Deviations from [AMOP]

This section lists the differences between the [AMOP] and the CLISP implementation thereof.

Not implemented in CLISP

- The generic function `CLOS:MAKE-METHOD-LAMBDA` is not implemented. See Section 29.5.3.2, “Generic Function Invocation Protocol”.

Features implemented differently in CLISP

- The class precedence list of `CLOS:FUNCALLABLE-STANDARD-OBJECT` is different. See Section 29.2.2, “Inheritance Structure of Metaobject Classes”.

- The `DEFCLASS` macro passes default values to `CLOS:ENSURE-CLASS`. See Section 29.3.1, “Macro `DEFCLASS`”.

- The `DEFGENERIC` macro passes default values to `ENSURE-GENERIC-FUNCTION`. See Section 29.5.3.1, “Macro `DEFGENERIC`”.

- The class `CLOS:FORWARD-REFERENCED-CLASS` is implemented differently. See Implementation of class `CLOS:FORWARD-REFERENCED-CLASS` in CLISP.

- The function `CLOS:GENERIC-FUNCTION-ARGUMENT-PRECEDENCE-ORDER` `SIGNAL`s an `ERROR` if the generic function has no lambda list.

- It is not possible to create a class with metaclass `STANDARD-CLASS` when specifying a superclass with metaclass `CLOS:FUNCALLABLE-STANDARD-CLASS`, even though `CLOS:VALIDATE-SUPERCLASS` returns `T` for this situation.

Extensions specific to CLISP

- The Meta-Object Protocol is applicable to classes of type `STRUCTURE-CLASS`. The default superclass for `STRUCTURE-CLASS` instances is `STRUCTURE-OBJECT`. Structure classes do not support multiple inheritance and reinitialization. See Section 29.3.5.1, “Initialization of class metaobjects”. See also Section 8.2, “The structure Meta-Object Protocol”.

- The `DEFGENERIC` macro supports user-defined options. See User-defined options.

- The class `METHOD` is subclassable. See Section 29.2.2, “Inheritance Structure of Metaobject Classes”.

- Slot names like `NIL` and `T` are allowed. See Section 29.4.2.1.1, “Generic Function `CLOS:SLOT-DEFINITION-NAME`”.

- The `CLOS:VALIDATE-SUPERCLASS` method is more permissive by default and does not need to be overridden in some “obvious” cases. See Section 29.3.6.7, “Generic Function `CLOS:VALIDATE-SUPERCLASS`”.

- New generic function `CLOS:COMPUTE-DIRECT-SLOT-DEFINITION-INITARGS`. It can sometimes be used when overriding `CLOS:DIRECT-SLOT-DEFINITION-CLASS` is cumbersome.

- New generic function `CLOS:COMPUTE-EFFECTIVE-SLOT-DEFINITION-INITARGS`. It can sometimes be used when overriding `CLOS:EFFECTIVE-SLOT-DEFINITION-CLASS` is cumbersome.

- New function `CLOS:COMPUTE-EFFECTIVE-METHOD-AS-FUNCTION`. It can be used in overriding methods of `CLOS:COMPUTE-DISCRIMINATING-FUNCTION`.

- The generic function `CLOS:ENSURE-GENERIC-FUNCTION-USING-CLASS` accepts a `:DECLARE` keyword.

- The functions `CLOS:FUNCALLABLE-STANDARD-INSTANCE-ACCESS` and `CLOS:STANDARD-INSTANCE-ACCESS` support non-updated obsolete instances and also support slots with allocation `:CLASS`.

- The existence of the function `CLOS:CLASS-DIRECT-SUBCLASSES` does not prevent otherwise unreferenced classes from being garbage-collected.

### 29.12.1. Warning `CLOS:CLOS-WARNING`

When CLISP encounters suspicious or suboptimal CLOS code, it issues a `WARNING` of type `CLOS:CLOS-WARNING` or a `STYLE-WARNING` of type `CLOS:CLOS-STYLE-WARNING`. To suppress the undesired warnings (not recommended!) use `EXT:SET-GLOBAL-HANDLER` with `MUFFLE-WARNING` on the appropriate `WARNING` type;. To find where the warnings come from (recommended), set `*BREAK-ON-SIGNALS*` to the appropriate `WARNING` type.

#### 29.12.1.1. Warning `CLOS:GF-ALREADY-CALLED-WARNING`

This is a hint that the order in which program files are loaded (order of definitions, order of macro expansions, or similar) may be wrong. Example:

    (defclass ware () ((title :initarg :title :accessor title)))
    (defclass book (ware) ())
    (defclass compact-disk (ware) ())
    (defclass dvd (ware) ())
    (defgeneric add-to-inventory (object))
    (defmethod add-to-inventory ((object ware)) nil)
    (add-to-inventory (make-instance 'book :title "CLtL1"))
    (defvar *book-counter* 0)
    (defmethod add-to-inventory ((object book)) (incf *book-counter*))
    (add-to-inventory (make-instance 'book :title "CLtL2"))
    *book-counter*
    ⇒ 1

Since [CLtL1] and [CLtL2] were already added to the inventory, the programmer might have expected that `*book-counter*` is 2.

### No warning for standard generic functions

A few functions, such as `PRINT-OBJECT`, are listed in the [ANSI CL standard] and the [AMOP] as “standard generic functions”, to which users may add methods. This warning is not issued for such functions.

### This is a `STYLE-WARNING`

This warning is actually a `STYLE-WARNING` because it indicates the behavior officially sanctioned by the standard and useful in some situations. We only warn on it because it may lead to confusing behavior for inexperienced users.

##### Motivation

A generic function is defined by a contract. Whoever adds a method to a generic function, however, also expects the contract to be fulfilled. (In the example above, the contract is that `*book-counter*` equals the number of invocations of `add-to-inventory` on `book` instances.) If the generic function has already been called before the method was added, the method's contract is definitely broken. Maybe the programmer has foreseen this case (in this example: he could initialize `*book-counter*` to the number of instances of `book` that exist at this moment, rather than to `0`), or maybe not. This is what the warning is about.

##### Disabling the warning for a specific generic function

If your generic function constitutes a public interface which is used by adding methods (similar to aforementioned `PRINT-OBJECT`), you can declare it as such:

    (defgeneric my-public-gf (a b c)
      (declare (clos:dynamically-modifiable))
      ...)

#### 29.12.1.2. Warning `CLOS:GF-REPLACING-METHOD-WARNING`

This is a hint that different parts of the program, possibly developed by independent people, are colliding. Example: in addition to the code above:

    (defvar *book-sales-statistics* (make-hash-table :test 'equal))
    (defmethod add-to-inventory ((object book))
      (setf (gethash (title object) sale-stats) (cons 0 0)))
    (add-to-inventory (make-instance 'book :title "AMOP"))
    *book-counter*
    ⇒ 1
    *book-sales-statistics*
    ⇒ #S(HASH-TABLE :TEST FASTHASH-EQUAL ("AMOP" . (0 . 0)))

The programmer who programmed the first ``add-to-inventory`@`book`` method expects that `*book-counter*` will be incremented. The programmer who programmed the second ``add-to-inventory`@`book`` method expects that `*book-sales-statistics*` gets augmented. If the implementation gives no warning, one of the two programmers will waste time debugging.

### This is a `STYLE-WARNING`

This warning is actually a `STYLE-WARNING` because it indicates the behavior officially sanctioned by the standard and useful in some situations. We only warn on it because it may lead to confusing behavior for inexperienced users.

##### Motivation

This warning can be warranted for the same reason as above: if the old method and the new method have a different contract, something is fishy and possibly wrong. Additionally, the programmers may not even have intended to replace the method. They may have intended cumulative effects of the two methods.

#### 29.12.1.3. Warning `CLOS:CLASS-OBSOLESCENCE-WARNING`

This is a hint that different parts of the program define the same `CLASS` incompatibly, and some objects, created to the old specification, have been obsoleted by the new one. Example: in addition to the code above:

    (defclass ware ()
      ((title :initarg :title :accessor title)
       (year :initarg :year :accessor year)))

Evaluating the above will obsolete all objects of type `ware`s, `book`s etc created so far, i.e., their components will become inaccessible.

### This is a `STYLE-WARNING`

This warning is actually a `STYLE-WARNING` because it indicates the behavior officially sanctioned by the standard and useful in some situations. We only warn on it because it may lead to confusing behavior for inexperienced users.

##### Motivation

In addition to the above, this warning tells the programmers that they are losing some objects they have already created.

## Chapter 30. Gray streams

## 30.1. Overview

This interface permits the definition of new classes of streams, and programming their behavior by defining methods for the elementary stream operations. It is based on the proposal STREAM-DEFINITION-BY-USER:GENERIC-FUNCTIONS of David N. Gray to X3J13 and is supported by most Common Lisp implementations currently in use.

All symbols defined by this interface, starting with the prefix `FUNDAMENTAL-` or `STREAM-`, are exported from the package “GRAY” and `EXT:RE-EXPORT`ed from “EXT”.

## 30.2. Defined classes

Defined classes

`GRAY:FUNDAMENTAL-STREAM`
  This is a superclass of all user-defined streams. It is a subclass of `STREAM` and of `STANDARD-OBJECT`. Its metaclass is `STANDARD-CLASS`.
`GRAY:FUNDAMENTAL-INPUT-STREAM`
  This is a superclass of all user-defined input `STREAM`s. It is a subclass of `GRAY:FUNDAMENTAL-STREAM`. The built-in function `INPUT-STREAM-P` returns true on instances of this class. This means that when you define a new stream class capable of doing input, you have to make it a subclass of `GRAY:FUNDAMENTAL-INPUT-STREAM`.
`GRAY:FUNDAMENTAL-OUTPUT-STREAM`
  This is a superclass of all user-defined output `STREAM`s. It is a subclass of `GRAY:FUNDAMENTAL-STREAM`. The built-in function `OUTPUT-STREAM-P` returns true on instances of this class. This means that when you define a new stream class capable of doing output, you have to make it a subclass of `GRAY:FUNDAMENTAL-OUTPUT-STREAM`.
`GRAY:FUNDAMENTAL-CHARACTER-STREAM`
  This is a superclass of all user-defined streams whose `STREAM-ELEMENT-TYPE` is `CHARACTER`. It is a subclass of `GRAY:FUNDAMENTAL-STREAM`. It defines a method on `STREAM-ELEMENT-TYPE` that returns `CHARACTER`.
`GRAY:FUNDAMENTAL-BINARY-STREAM`
  This is a superclass of all user-defined streams whose `STREAM-ELEMENT-TYPE` is a subtype of `INTEGER`. It is a subclass of `GRAY:FUNDAMENTAL-STREAM`. When you define a subclass of `GRAY:FUNDAMENTAL-BINARY-STREAM`, you have to provide a method on `STREAM-ELEMENT-TYPE`.
`GRAY:FUNDAMENTAL-CHARACTER-INPUT-STREAM`
  This is a convenience class inheriting from both `GRAY:FUNDAMENTAL-CHARACTER-STREAM` and `GRAY:FUNDAMENTAL-INPUT-STREAM`.
`GRAY:FUNDAMENTAL-CHARACTER-OUTPUT-STREAM`
  This is a convenience class inheriting from both `GRAY:FUNDAMENTAL-CHARACTER-STREAM` and `GRAY:FUNDAMENTAL-OUTPUT-STREAM`.
`GRAY:FUNDAMENTAL-BINARY-INPUT-STREAM`
  This is a convenience class inheriting from both `GRAY:FUNDAMENTAL-BINARY-STREAM` and `GRAY:FUNDAMENTAL-INPUT-STREAM`.
`GRAY:FUNDAMENTAL-BINARY-OUTPUT-STREAM`
  This is a convenience class inheriting from both `GRAY:FUNDAMENTAL-BINARY-STREAM` and `GRAY:FUNDAMENTAL-OUTPUT-STREAM`.

## 30.3. General generic functions

General generic functions defined on streams

`(`STREAM-ELEMENT-TYPE` `stream`)`

  Returns the stream's element type, normally a subtype of `CHARACTER` or `INTEGER`.

  The method for `GRAY:FUNDAMENTAL-CHARACTER-STREAM` returns `CHARACTER`.

`((`SETF` `STREAM-ELEMENT-TYPE`) `new-element-type` `stream`)`

  Changes the stream's element type.

  The default method `SIGNAL`s an `ERROR`.

  This function is a CLISP extension (see Section 21.8, “Function `STREAM-ELEMENT-TYPE`”).

`(`CLOSE` `stream` `&KEY` `:ABORT`)`

  Closes the stream and flushes any associated buffers.

  When you define a primary method on this function, do not forget to `CALL-NEXT-METHOD`.

`(`OPEN-STREAM-P` `stream`)`

  Returns true before the stream has been closed, and `NIL` after the stream has been closed.

  You do not need to add methods to this function.

`(`GRAY:STREAM-POSITION` `stream` `position`)`

  Just like `FILE-POSITION`, but `NIL` `position` means inquire.

  You must define a method for this function.

`(GRAY:STREAM-READ-SEQUENCE `sequence` `stream` `&KEY` `:START` `:END`)`

  Used by `READ-SEQUENCE`. Deprecated. Define `GRAY:STREAM-READ-CHAR-SEQUENCE` or `GRAY:STREAM-READ-BYTE-SEQUENCE` and call `EXT:READ-CHAR-SEQUENCE`/`EXT:READ-BYTE-SEQUENCE` instead.

  The default method calls `GRAY:STREAM-READ-CHAR-SEQUENCE` or `GRAY:STREAM-READ-BYTE-SEQUENCE`.

`(GRAY:STREAM-WRITE-SEQUENCE `sequence` `stream` `&KEY` `:START` `:END`)`

  Used by `WRITE-SEQUENCE`. Deprecated. Define `GRAY:STREAM-WRITE-CHAR-SEQUENCE` or `GRAY:STREAM-WRITE-BYTE-SEQUENCE` and call `EXT:WRITE-CHAR-SEQUENCE`/`EXT:WRITE-BYTE-SEQUENCE` instead.

  The default method calls `GRAY:STREAM-WRITE-CHAR-SEQUENCE` or `GRAY:STREAM-WRITE-BYTE-SEQUENCE`.

## 30.4. Generic functions for character input

Generic functions for character input

`(`GRAY:STREAM-READ-CHAR` `stream`)`

  If a character was pushed back using `GRAY:STREAM-UNREAD-CHAR`, returns and consumes it. Otherwise returns and consumes the next character from the stream. Returns `:EOF` if the `end-of-stream` is reached.

  You must define a method for this function.

`(`GRAY:STREAM-UNREAD-CHAR` `stream` `char`)`

  Pushes `char`, which must be the last character read from the `stream`, back onto the front of the `stream`.

  You must define a method for this function.

`(`GRAY:STREAM-READ-CHAR-NO-HANG` `stream`)`

  Returns a character or `:EOF`, like `GRAY:STREAM-READ-CHAR`, if that would return immediately. If `GRAY:STREAM-READ-CHAR`'s value is not available immediately, returns `NIL` instead of waiting.

  The default method simply calls `GRAY:STREAM-READ-CHAR`; this is sufficient for streams whose `GRAY:STREAM-READ-CHAR` method never blocks.

`(GRAY:STREAM-PEEK-CHAR `stream`)`

  If a character was pushed back using `GRAY:STREAM-UNREAD-CHAR`, returns it. Otherwise returns the next character from the stream, avoiding any side effects `GRAY:STREAM-READ-CHAR` would do. Returns `:EOF` if the `end-of-stream` is reached.

  The default method calls `GRAY:STREAM-READ-CHAR` and `GRAY:STREAM-UNREAD-CHAR`; this is sufficient for streams whose `GRAY:STREAM-READ-CHAR` method has no side-effects.

`(GRAY:STREAM-LISTEN `stream`)`

  If a character was pushed back using `GRAY:STREAM-UNREAD-CHAR`, returns it. Otherwise returns the next character from the stream, if already available. If no character is available immediately, or if `end-of-stream` is reached, returns `NIL`.

  The default method calls `GRAY:STREAM-READ-CHAR-NO-HANG` and `GRAY:STREAM-UNREAD-CHAR`; this is sufficient for streams whose `GRAY:STREAM-READ-CHAR` method has no side-effects.

`(GRAY:STREAM-READ-CHAR-WILL-HANG-P `stream`)`

  Returns `NIL` if `GRAY:STREAM-READ-CHAR` will return immediately. Otherwise it returns true.

  The default method calls `GRAY:STREAM-READ-CHAR-NO-HANG` and `GRAY:STREAM-UNREAD-CHAR`; this is sufficient for streams whose `GRAY:STREAM-READ-CHAR` method has no side-effects.

  This function is a CLISP extension (see `EXT:READ-CHAR-WILL-HANG-P`).

`(`GRAY:STREAM-READ-CHAR-SEQUENCE` `stream` `sequence` `&OPTIONAL` [`start` [`end`]])`

  Fills the subsequence of `sequence` specified by `:START` and `:END` with characters consecutively read from `stream`. Returns the index of the first element of `sequence` that was not updated (`=` `end`, or `<` `end` if the stream reached its end).

  `sequence` is an `ARRAY` of `CHARACTER`s, i.e. a `STRING`. `start` is a nonnegative `INTEGER` and defaults to `0`. `end` is a nonnegative `INTEGER` or `NIL` and defaults to `NIL`, which stands for `(`LENGTH` `sequence`)`.

  The default method repeatedly calls `GRAY:STREAM-READ-CHAR`; this is always sufficient if speed does not matter.

  This function is a CLISP extension (see `EXT:READ-CHAR-SEQUENCE`).

`(GRAY:STREAM-READ-LINE `stream`)`

  Reads a line of characters, and return two values: the line (a `STRING`, without the terminating #\Newline character), and a `BOOLEAN` value which is true if the line was terminated by `end-of-stream` instead of #\Newline.

  The default method repeatedly calls `GRAY:STREAM-READ-CHAR`; this is always sufficient.

`(GRAY:STREAM-CLEAR-INPUT `stream`)`

  Clears all pending interactive input from the `stream`, and returns true if some pending input was removed.

  The default method does nothing and returns `NIL`; this is sufficient for non-interactive streams.

## 30.5. Generic functions for character output

Generic functions for character output

`(`GRAY:STREAM-WRITE-CHAR` `stream` `char`)`

  Writes `char`.

  You must define a method for this function.

`(`GRAY:STREAM-LINE-COLUMN` `stream`)`

  Returns the column number where the next character would be written (`0` stands for the first column), or `NIL` if that is not meaningful for this stream.

  You must define a method for this function.

`(GRAY:STREAM-START-LINE-P `stream`)`

  Returns true if the next character would be written at the start of a new line.

  The default method calls `GRAY:STREAM-LINE-COLUMN` and compares its result with 0; this is sufficient for streams whose `GRAY:STREAM-LINE-COLUMN` never returns `NIL`.

`(`GRAY:STREAM-WRITE-CHAR-SEQUENCE` `stream` `sequence` `&OPTIONAL` [`start` [`end`]])`

  Outputs the subsequence of `sequence` specified by `:START` and `:END` to `stream`.

  `sequence` is an `ARRAY` of `CHARACTER`s, i.e. a `STRING`. `start` is a nonnegative `INTEGER` and defaults to 0. `end` is a nonnegative integer or `NIL` and defaults to `NIL`, which stands for `(`LENGTH` `sequence`)`.

  The default method repeatedly calls `GRAY:STREAM-WRITE-CHAR`; this is always sufficient if speed does not matter.

  This function is a CLISP extension (see `EXT:WRITE-CHAR-SEQUENCE`).

`(GRAY:STREAM-WRITE-STRING `stream` `string` `&OPTIONAL` [`start` [`end`]])`

  Outputs the subsequence of `string` specified by `:START` and `:END` to `stream`. Returns `string`.

  `string` is a string. `start` is a nonnegative integer and default to 0. `end` is a nonnegative integer or `NIL` and defaults to `NIL`, which stands for `(`LENGTH` `string`)`.

  The default method calls `GRAY:STREAM-WRITE-CHAR-SEQUENCE`; this is always sufficient.

`(GRAY:STREAM-TERPRI `stream`)`

  Outputs a #\Newline character.

  The default method calls `GRAY:STREAM-WRITE-CHAR`; this is always sufficient.

`(GRAY:STREAM-FRESH-LINE `stream`)`

  Possibly outputs a #\Newline character, so as to ensure that the next character would be written at the start of a new line. Returns true if it did output a #\Newline character.

  The default method calls `GRAY:STREAM-START-LINE-P` and then `GRAY:STREAM-TERPRI` if necessary; this is always sufficient.

`(GRAY:STREAM-FINISH-OUTPUT `stream`)`

  Ensures that any buffered output has reached its destination, and then returns.

  The default method does nothing.

`(GRAY:STREAM-FORCE-OUTPUT `stream`)`

  Brings any buffered output on its way towards its destination, and returns without waiting until it has reached its destination.

  The default method does nothing.

`(GRAY:STREAM-CLEAR-OUTPUT `stream`)`

  Attempts to discard any buffered output which has not yet reached its destination.

  The default method does nothing.

`(GRAY:STREAM-ADVANCE-TO-COLUMN `stream` `column`)`

  Ensures that the next character will be written at least at `column`.

  The default method outputs an appropriate amount of space characters; this is sufficient for non-proportional output.

## 30.6. Generic functions for binary input

Generic functions for binary input

`(`GRAY:STREAM-READ-BYTE` `stream`)`

  Returns and consumes the next integer from the stream. Returns `:EOF` if the `end-of-stream` is reached.

  You must define a method for this function.

`(`GRAY:STREAM-READ-BYTE-LOOKAHEAD` `stream`)`

  To be called only if `stream`'s `STREAM-ELEMENT-TYPE` is `(`UNSIGNED-BYTE` 8)` or `(`SIGNED-BYTE` 8)`. Returns `T` if `GRAY:STREAM-READ-BYTE` would return immediately with an `INTEGER` result. Returns `:EOF` if the `end-of-stream` is already known to be reached. If `GRAY:STREAM-READ-BYTE`'s value is not available immediately, returns `NIL` instead of waiting.

  You must define a method for this function.

  This function is a CLISP extension (see `EXT:READ-BYTE-LOOKAHEAD`).

`(`GRAY:STREAM-READ-BYTE-WILL-HANG-P` `stream`)`

  To be called only if `stream`'s `STREAM-ELEMENT-TYPE` is `(`UNSIGNED-BYTE` 8)` or `(`SIGNED-BYTE` 8)`. Returns `NIL` if `GRAY:STREAM-READ-BYTE` will return immediately. Otherwise it returns true.

  The default method calls `GRAY:STREAM-READ-BYTE-LOOKAHEAD`; this is always sufficient.

  This function is a CLISP extension (see `EXT:READ-BYTE-WILL-HANG-P`).

`(`GRAY:STREAM-READ-BYTE-NO-HANG` `stream`)`

  To be called only if `stream`'s `STREAM-ELEMENT-TYPE` is `(`UNSIGNED-BYTE` 8)` or `(`SIGNED-BYTE` 8)`. Returns an `INTEGER` or `:EOF`, like `GRAY:STREAM-READ-BYTE`, if that would return immediately. If `GRAY:STREAM-READ-BYTE`'s value is not available immediately, returns `NIL` instead of waiting.

  The default method calls `GRAY:STREAM-READ-BYTE` if `GRAY:STREAM-READ-BYTE-LOOKAHEAD` returns true; this is always sufficient.

  This function is a CLISP extension (see `EXT:READ-BYTE-NO-HANG`).

`(`GRAY:STREAM-READ-BYTE-SEQUENCE` `stream` `sequence` `&OPTIONAL` [`start` [`end` [`no-hang` [`interactive`]]]])`

  Fills the subsequence of `sequence` specified by `:START` and `:END` with integers consecutively read from `stream`. Returns the index of the first element of `sequence` that was not updated (`=` `end`, or `<` `end` if the stream reached its end).

  `sequence` is an `ARRAY` of `INTEGER`s. `start` is a nonnegative `INTEGER` and defaults to 0. `end` is a nonnegative `INTEGER` or `NIL` and defaults to `NIL`, which stands for `(`LENGTH` `sequence`)`. If `no-hang` is true, the function should avoid blocking and instead fill only as many elements as are immediately available. If `no-hang` is false and `interactive` is true, the function can block for reading the first byte but should avoid blocking for any further bytes.

  The default method repeatedly calls `GRAY:STREAM-READ-BYTE`; this is always sufficient if speed does not matter.

  This function is a CLISP extension (see `EXT:READ-BYTE-SEQUENCE`).

## 30.7. Generic functions for binary output

Generic functions for binary output

`(GRAY:STREAM-WRITE-BYTE `stream` `integer`)`

  Writes `integer`.

  You must define a method for this function.

`(`GRAY:STREAM-WRITE-BYTE-SEQUENCE` `stream` `sequence` `&OPTIONAL` [`start` [`end` [`no-hang` [`interactive`]]]])`

  Outputs the subsequence of `sequence` specified by `:START` and `:END` to `stream`

  `sequence` is an `ARRAY` of `INTEGER`s. `start` is a nonnegative `INTEGER` and defaults to 0. `end` is a nonnegative `INTEGER` or `NIL` and defaults to `NIL`, which stands for `(`LENGTH` `sequence`)`. If `no-hang` is true, the function should avoid blocking and instead output only as many elements as it can immediately proceed. If `no-hang` is false and `interactive` is true, the function can block for writing the first byte but should avoid blocking for any further bytes.

  The default method repeatedly calls `GRAY:STREAM-WRITE-BYTE`; this is always sufficient if speed does not matter.

  This function is a CLISP extension (see `EXT:WRITE-BYTE-SEQUENCE`).

## 30.8. Class `EXT:FILL-STREAM`

List of Examples

30.1. Example of `EXT:FILL-STREAM` usage

As an example of the use of “GRAY” `STREAM`s, CLISP offers an additional class, `EXT:FILL-STREAM`. An instance of this class is a “formatting” `STREAM`, which makes the final output to the underlying stream look neat: indented and filled. An instance of `EXT:FILL-STREAM` is created like this:

    (MAKE-INSTANCE 'EXT:FILL-STREAM :stream stream
                   [:text-indent symbol-or-number]
                   [:sexp-indent symbol-or-number-or-function])

where

`stream`
  is the target `STREAM` where the output actually goes.
`symbol-or-number`
  is the variable whose value is the `INTEGER` text indentation or the indentation itself (defaults to 0).
`symbol-or-number-or-function`

  When `FORMAT` writes an S-expression to a `EXT:FILL-STREAM` using `~S`, and the expression's printed representation does not fit on the current line, it is printed on separate lines, ignoring the prescribed text indentation and preserving spacing. When this argument is non-`NIL`, the S-expression is indented by:

  `T`
    the text indentation above;
  `SYMBOL`
    `SYMBOL-VALUE` is the indentation;
  `INTEGER`
    the indentation itself;
  `FUNCTION`
    called with one argument, the text indentation, and the value is used as S-expression indentation; thus `IDENTITY` is equivalent to `T` above.

  Defaults to `CUSTOM:*FILL-INDENT-SEXP*`, whose initial value is `1+`.

### Warning

Note that, due to buffering, one must call `FORCE-OUTPUT` when done with the `EXT:FILL-STREAM` (and before changing the indent variable). The former is done automatically by the macro `(with-fill-stream (fill target-stream ...) ...)`.

Example 30.1. Example of `EXT:FILL-STREAM` usage

    (defvar *my-indent-level*)
    (with-output-to-string (out)
      (let ((*print-right-margin* 20)
            (*print-pretty* t)
            (*my-indent-level* 2))
        (with-fill-stream (fill out :text-indent '*my-indent-level*)
          (format fill "~%this is some long sentence which will      be broken at spaces")
          (force-output fill)
          (let ((*my-indent-level* 5))
            (format fill "~%and    properly indented to the level specified by the ~S argument which can be a ~S or an ~S - cool!"
                    :TEXT-INDENT 'symbol 'integer)
            (force-output fill))
          (format fill "~%Don't forget  to call ~S on it, and/or use ~S   Pretty formatting of the  S-expressions    printed with ~~S is  preserved: ~S"
                  'force-output 'with-fill-stream '(defun foo (x y z) (if x (+ y z) (* y z)))))))
    ⇒ "
      this is some long
      sentence which
      will be broken at
      spaces
         and properly
         indented to
         the level
         specified by
         the
         :TEXT-INDENT
         argument which
         can be a
         SYMBOL or an
         INTEGER -
         cool!
      Don't forget to
      call FORCE-OUTPUT
      on it, and/or use
      WITH-FILL-STREAM
      Pretty formatting
      of the
      S-expressions
      printed with ~S
      is preserved:
       (DEFUN FOO
        (X Y Z)
        (IF X (+ Y Z)
         (* Y Z)))
    "

# Part III. Extensions Specific to CLISP

## Chapter 31. Platform Independent Extensions

## 31.1. Customizing CLISP Process Initialization and Termination

### 31.1.1. Cradle to Grave

#### What is done when

1. Initialization

   1. Parse command line arguments until the first positional argument (see `:SCRIPT`).

   2. Load the memory image.

   3. Install internal signal handlers.

   4. Initialize time variables.

   5. Initialize locale-dependent encodings.

   6. Initialize stream variables.

   7. Initialize pathname variables.

   8. Initialize “FFI”.

   9. Initialize modules.

   10. Run all functions in `CUSTOM:*INIT-HOOKS*`.

   11. Say “hi”, unless suppressed by `-q`.

   12. Load RC file, unless suppressed by `-norc`.

2. The actual work

   Handle command line options: file loading and/or compilation, form evaluation, script execution, read-eval-print loop.

3. Finalization (executed even on abnormal exit due to `kill`)

   1. Unwind the `STACK`, executing cleanup forms in `UNWIND-PROTECT`.

   2. Run all functions in `CUSTOM:*FINI-HOOKS*`.

   3. Call `FRESH-LINE` on the standard streams.

   4. Say “bye” unless suppressed by `-q`.

   5. Wait for a keypress if requested by `-w`.

   6. Close all open `FILE-STREAM`s.

   7. Finalize modules.

   8. Close all open DLLs.

### 31.1.2. Customizing Initialization

`CUSTOM:*INIT-HOOKS*` is run like this:

    (IGNORE-ERRORS (MAPC #'FUNCALL CUSTOM:*INIT-HOOKS*))

#### 31.1.2.1. The difference between `CUSTOM:*INIT-HOOKS*` and init function

- `CUSTOM:*INIT-HOOKS*` are always run regardless of the command line options before even the banner is printed.
- The init function is run only if the read-eval-print loop is ever entered and just before the first prompt is printed.

### 31.1.3. Customizing Termination

`CUSTOM:*FINI-HOOKS*` is run like this:

    (MAPC #'FUNCALL CUSTOM:*FINI-HOOKS*)

## 31.2. Saving an Image

The function `(`EXT:SAVEINITMEM` `&OPTIONAL` (`filename` "lispinit.mem") `&KEY` :KEEP-GLOBAL-HANDLERS :QUIET :INIT-FUNCTION :LOCKED-PACKAGES :START-PACKAGE :EXECUTABLE :NORC :SCRIPT :DOCUMENTATION :VERBOSE)` saves the running CLISP's memory to the file `filename`; extension `#P".mem"` is recommended (when `filename` does not have an extension, `#P".mem"` extension is automatically added unless the file being created is an executable).

`:QUIET`

  If this argument is not `NIL`, the startup banner and the good-bye message will be suppressed, as if by `-q`.

  This is not recommended for interactive application delivery, please append your banner to ours (using init function) instead of replacing it.

`:VERBOSE`
  Print a message after writing the file. This argument defaults to `CUSTOM:*SAVEINITMEM-VERBOSE*`; initial value is `T`.
`:NORC`
  If this argument is not `NIL`, the RC file loading will be suppressed, as if by `-norc`.
`:INIT-FUNCTION`

  This argument specifies a function that will be executed at startup of the saved image, before entering the standard read-eval-print loop (but after all other initialization, see Section 31.1.1, “Cradle to Grave”); thus, if you want to avoid the read-eval-print loop, you have to call `EXT:EXIT` at the end of the init function yourself (this does not prevent `CUSTOM:*FINI-HOOKS*` from being run).

  See the manual for passing command line arguments to this function.

  See also `CUSTOM:*INIT-HOOKS*` and `CUSTOM:*FINI-HOOKS*`.

`:SCRIPT`

  This options determines the handling of positional arguments when the image is invoked.

  - If it is `T`, then the first positional argument is the script name and the rest is placed into `EXT:*ARGS*`, as described in Section 32.6.2, “Scripting with CLISP”.
  - It it is `NIL`, then all positional arguments are placed into `EXT:*ARGS*` to be handled by the init function.

  This option defaults to `T` when init function is `NIL` and to `NIL` when init function is non-`NIL`.

`:DOCUMENTATION`

  The description of what this image does, printed by the `-help-image` olption.

  Defaults to `(`DOCUMENTATION` init function '`FUNCTION`)`

`:LOCKED-PACKAGES`
  This argument specifies the packages to lock before saving the image; this is convenient for application delivery, when you do not want your users to mess up your product. This argument defaults to `CUSTOM:*SYSTEM-PACKAGE-LIST*`.
`:START-PACKAGE`
  This argument specifies the starting value of `*PACKAGE*` in the image being saved, and defaults to the current value of `*PACKAGE*`.
`:KEEP-GLOBAL-HANDLERS`

  When non-`NIL`, the currently established global handlers (either with `EXT:SET-GLOBAL-HANDLER` or with `-on-error`) are inherited by the image. Defaults to `NIL`, so that

      $ clisp -i myfile -x '(EXT:SAVEINITMEM)'

  will produce an image without any global handlers inherited from the batch mode of the above command.

`:EXECUTABLE`

  When non-`NIL`, the saved file will be a standalone executable. In this case, the `#P".mem"` extension is not added. On Win32 and Cygwin the extension `#P".exe"` is added instead.

  Additionally, if this argument is `0`, the standard CLISP command line options will not be processed by the executable but will be placed into `EXT:*ARGS*` instead. This is convenient for application delivery, so that your CLISP-based application can accept, e.g., `-x`. To override this feature of the image, you have to prefix the options with `"--clisp"`, e.g., use `--clisp-x` instead of `-x`. This, given such a CLISP-based application, you can get to an ordinary CLISP read-eval-print loop by doing

      $ application --clisp-x '(EXT:SAVEINITMEM "myclisp" :executable t :init-function nil)'
      $ ./myclisp
      [1]> (! 20)
      2432902008176640000

  These instructions are also printed by `--clisp--help`.

  Of course, this feature opens a security hole if the application is running `setuid` root, therefore CLISP resets the effective group and user IDs to the real ones if it sees a `"--clisp-*"` option.

You can use this memory image with the `-M` option. On UNIX systems, you may compress it with GNU gzip to save disk space.

### 31.2.1. Image Portability

Memory images are not portable across different platforms (in contrast with platform-independent `#P".fas"` files). They are not even portable across linking sets: image saved using the full linking set cannot be used with the base runtime:

    $ clisp -K full -x '(EXT:SAVEINITMEM)'
    $ clisp -K base -M lispinit.mem
    base/lisp.run: initialization file `lispinit.mem' was not created by this version of CLISP runtime

See also `Gmane/devel/17757`/https://sourceforge.net/p/clisp/mailman/message/18854510/.

### 31.2.2. Distributing images in package repositories

When CLISP and packages that rely on CLISP are distributed through package repositories, such as operating system distributions, the way the memory images work imposes certain ways to handle them in the packaging system.

Assume you have a package `foo` that relies on CLISP. There are three ways to package it:

- It can be packaged to not use a memory image. Instead the program `foo` is an invocation of clisp that will load a set of `*.fas` files at startup. You can simplify this loading by concatenating the `*.fas` files together; then only a single `*.fas` file needs to be loaded. The drawback of this approach is the startup time.

- It can be packaged to use a memory image that is constructed in a subdirectory of `/var/lib`, when `foo` gets installed, through a post-install action of package `foo`. Also the package `clisp` will have a post-install action that removes and rebuilds these memory images when a new version of `clisp` is installed.

- It can be packaged to use a memory image that is part of the binary package of `foo` and installed in a subdirectory of `/usr/lib`. In order to catch the case where `clisp` is upgraded and `foo` is not upgraded, you attach an alias `clisp-`memory-image-interface-hash`` to the `clisp` package, and you make the `foo` package depend on this alias. When the `clisp` package is upgraded (or even when it is only rebuilt with a different parameterization), the `memory-image-interface-hash` changes, and the packaging system will notice a dependency conflict. A good packaging system will then propose one of two actions to the user:

  - either upgrade package `foo` as well, to a build that depends on the new `clisp-`memory-image-interface-hash`` alias (assuming such a build exists),

  - or refuse the upgrade of `clisp`.

  To allow you to implement such a system, CLISP provides the following command-line options:

  `clisp [-K `linking-set`] -memfile-hash`
    Prints the hash code of the mem file binary interface.
  `clisp [-K `linking-set`] -memfile-hash-of `mem-file``
    Prints the hash code of the mem file binary interface that was used to create this `mem-file`.
  `clisp [-K `linking-set`] -memfile-compatible `mem-file``
    Returns 0 or 1, depending whether this `mem-file` is compatible with the `linking-set` or not.

  When the hash code of the mem file binary interface of a CLISP executable is the same as the one of a `mem-file`, it is guaranteed that the executable can load this `mem-file`.

## 31.3. Quitting CLISP

The functions

`(`EXT:EXIT` `&OPTIONAL` `status`)`
`(EXT:QUIT `&OPTIONAL` `status`)`
`(EXT:BYE `&OPTIONAL` `status`)`

- all synonymous - terminate CLISP. If `status` is non-`NIL`, CLISP aborts with the supplied numeric error `status`, i.e., the OS environment is informed that the CLISP session did not succeed.

Final delimiters also terminate CLISP.

## 31.4. Internationalization of CLISP

Glossary

Internationalization (“i18n”)
  preparing a program so that it can use multiple national languages and national cultural conventions without requiring further source code changes.
Localization (“l10n”)
  providing the data - mostly textual translations - necessary for an internationalized program to work in a particular language and with particular cultural conventions.

CLISP is internationalized, and is localized for the languages English, German, French, Spanish, Dutch, Russian, and Danish. CLISP also supports internationalized Lisp programs, through GNU gettext, see Section 33.3, “Internationalization of User Programs”.

### 31.4.1. The Language

### Warning

The facilities described in this section will work only for the languages for which CLISP itself is already localized.

The language CLISP uses to communicate with the user can be one of

`ENGLISH`
`DEUTSCH` (i.e., German)
`FRANÇAIS` (i.e., French)
`ESPAÑOL` (i.e., Spanish)
`NEDERLANDS` (i.e., Dutch)
`РУССКИЙ` (i.e. Russian)
`DANSK` (i.e., Danish)

This is controlled by the `SYMBOL-MACRO` `CUSTOM:*CURRENT-LANGUAGE*`, which can be set at run time as well as using the `-L` command line option. If you wish to change the locale directory at run time too, you can do that by setting `CUSTOM:*CURRENT-LANGUAGE*` to a `CONS` cell, whose `CAR` is the language (a `SYMBOL`, one of the above), and whose `CDR` is the new locale directory.

More languages can be defined through the macro `I18N:DEFLANGUAGE`: `(`I18N:DEFLANGUAGE` `language`)`. For such an additional language to take effect, you must install the corresponding message catalog, or translate the messages yourself, using GNU gettext and Emacs po-mode.

This works only for strings. For arbitrary language-dependent Lisp objects, you define one through the macro `I18N:DEFINTERNATIONAL`: `(`I18N:DEFINTERNATIONAL` `symbol` `&OPTIONAL` (`default-language` `T`))` and add language-dependent values through the macro `I18N:DEFLOCALIZED`: `(`I18N:DEFLOCALIZED` `symbol` `language` `value-form`)` (One such form for each language. Languages without an assigned value will be treated like the default-language.) You can then access the localized value by calling `I18N:LOCALIZED`: `(`I18N:LOCALIZED` `symbol` `&OPTIONAL` `language`)`

## 31.5. Encodings

### 31.5.1. Introduction

An “encoding” describes the correspondence between `CHARACTER`s and raw bytes during input/output via `STREAM`s with `STREAM-ELEMENT-TYPE` `CHARACTER`.

An `EXT:ENCODING` is an object composed of the following facets:

character set
  This denotes both the set of `CHARACTER`s that can be represented and passed through the I/O channel, and the way these characters translate into raw bytes, i.e., the map between sequences of `CHARACTER` and `(`UNSIGNED-BYTE` 8)` in the form of `STRING`s and `(`VECTOR` (`UNSIGNED-BYTE` 8))` as well as character and byte `STREAM`s. In this context, for example, `CHARSET:UTF-8` and `CHARSET:UCS-4` are considered different, although they can represent the same set of characters.
line terminator mode
  This denotes the way newline characters are represented.

`EXT:ENCODING`s are also `TYPE`s. As such, they represent the set of characters encodable in the character set. In this context, the way characters are translated into raw bytes is ignored, and the line terminator mode is ignored as well. `TYPEP` and `SUBTYPEP` can be used on encodings:

    (SUBTYPEP CHARSET:UTF-8 CHARSET:UTF-16)
    ⇒ T ;
    ⇒ T
    (SUBTYPEP CHARSET:UTF-16 CHARSET:UTF-8)
    ⇒ T ;
    ⇒ T
    (SUBTYPEP CHARSET:ASCII CHARSET:ISO-8859-1)
    ⇒ T ;
    ⇒ T
    (SUBTYPEP CHARSET:ISO-8859-1 CHARSET:ASCII)
    ⇒ NIL ;
    ⇒ T

“1:1” encodings. Encodings which define a bijection between character and byte sequences are called “1:1” encodings. `CHARSET:ISO-8859-1` is an example of such an encoding: any byte sequence corresponds to some character sequence and vice versa. ASCII, however, is not a “1:1” encoding: there are no characters for bytes in the range [128;255]. `CHARSET:UTF-8` is not a “1:1” encoding either: some byte sequences do not correspond to any character sequence.

### 31.5.2. Character Sets

Platform Dependent: Only in CLISP built without compile-time flag UNICODE
  Only one character set is understood: the platform's native (8-bit) character set. See Chapter 13, Characters chap-13.
Platform Dependent: Only in CLISP built with compile-time flag UNICODE

  The following character sets are supported, as values of the corresponding (constant) symbol in the “CHARSET” package:

  Symbols in package “CHARSET”

  1. `UCS-2` ≡ `UNICODE-16` ≡ `UNICODE-16-BIG-ENDIAN`, the 16-bit basic multilingual plane of the UNICODE character set. Every character is represented as two bytes.
  2. `UNICODE-16-LITTLE-ENDIAN`
  3. `UCS-4` ≡ `UNICODE-32` ≡ `UNICODE-32-BIG-ENDIAN`, the 21-bit UNICODE character set. Every character is represented as four bytes. This encoding is used by CLISP internally.
  4. `UNICODE-32-LITTLE-ENDIAN`
  5. `UTF-8`, the 21-bit UNICODE character set. Every character is represented as one to four bytes. ASCII characters represent themselves and need one byte per character. Most Latin/Greek/Cyrillic/Hebrew characters need two bytes per character. Most other characters need three bytes per character, and the rarely used remaining characters need four bytes per character. This is therefore, in general, the most space-efficient encoding of all of Unicode.
  6. `UTF-16`, the 21-bit UNICODE character set. Every character in the 16-bit basic multilingual plane is represented as two bytes, and the rarely used remaining characters need four bytes per character. This character set is only available on platforms with GNU libc or GNU libiconv.
  7. `UTF-7`, the 21-bit UNICODE character set. This is a stateful 7-bit encoding. Not all ASCII characters represent themselves. This character set is only available on platforms with GNU libc or GNU libiconv.
  8. `JAVA`, the 21-bit UNICODE character set. ASCII characters represent themselves and need one byte per character. All other characters of the basic multilingual plane are represented by `\u`nnnn`` sequences (`nnnn` a hexadecimal number) and need 6 bytes per character. The remaining characters are represented by `\u`xxxx`\u`yyyy`` and need 12 bytes per character. While this encoding is very comfortable for editing Unicode files using only ASCII-aware tools and editors, it cannot faithfully represent all UNICODE text. Only text which does not contain `\u` (backslash followed by lowercase Latin u) can be faithfully represented by this encoding.
  9. `ASCII`, the well-known US-centric 7-bit character set (American Standard Code for Information Interchange - ASCII).

  10. `ISO-8859-1`, an extension of the ASCII character set, suitable for the Afrikaans, Albanian, Basque, Breton, Catalan, Cornish, Danish, Dutch, English, Færoese, Finnish, French, Frisian, Galician, German, Greenlandic, Icelandic, Irish, Italian, Latin, Luxemburgish, Norwegian, Portuguese, Ræto-Romanic, Scottish, Spanish, and Swedish languages.

      This encoding has the nice property that

          (LOOP :for i :from 0 :to CHAR-CODE-LIMIT :for c = (CODE-CHAR i)
            :always (OR (NOT (TYPEP c CHARSET:ISO-8859-1))
                        (EQUALP (EXT:CONVERT-STRING-TO-BYTES (STRING c) CHARSET:ISO-8859-1)
                                (VECTOR i))))
          ⇒ T

      i.e., it is compatible with CLISP `CODE-CHAR`/`CHAR-CODE` in its own domain.

  11. `ISO-8859-2`, an extension of the ASCII character set, suitable for the Croatian, Czech, German, Hungarian, Polish, Slovak, Slovenian, and Sorbian languages.
  12. `ISO-8859-3`, an extension of the ASCII character set, suitable for the Esperanto and Maltese languages.
  13. `ISO-8859-4`, an extension of the ASCII character set, suitable for the Estonian, Latvian, Lithuanian and Sami (Lappish) languages.
  14. `ISO-8859-5`, an extension of the ASCII character set, suitable for the Bulgarian, Byelorussian, Macedonian, Russian, Serbian, and Ukrainian languages.
  15. `ISO-8859-6`, suitable for the Arabic language.
  16. `ISO-8859-7`, an extension of the ASCII character set, suitable for the Greek language.
  17. `ISO-8859-8`, an extension of the ASCII character set, suitable for the Hebrew language (without punctuation).
  18. `ISO-8859-9`, an extension of the ASCII character set, suitable for the Turkish language.
  19. `ISO-8859-10`, an extension of the ASCII character set, suitable for the Estonian, Icelandic, Inuit (Greenlandic), Latvian, Lithuanian, and Sami (Lappish) languages.
  20. `ISO-8859-13`, an extension of the ASCII character set, suitable for the Estonian, Latvian, Lithuanian, Polish and Sami (Lappish) languages.
  21. `ISO-8859-14`, an extension of the ASCII character set, suitable for the Irish Gælic, Manx Gælic, Scottish Gælic, and Welsh languages.
  22. `ISO-8859-15`, an extension of the ASCII character set, suitable for the ISO-8859-1 languages, with improvements for French, Finnish and the Euro.
  23. `ISO-8859-16` an extension of the ASCII character set, suitable for the Rumanian language.
  24. `KOI8-R`, an extension of the ASCII character set, suitable for the Russian language (very popular, especially on the internet).
  25. `KOI8-U`, an extension of the ASCII character set, suitable for the Ukrainian language (very popular, especially on the internet).
  26. `KOI8-RU`, an extension of the ASCII character set, suitable for the Russian language. This character set is only available on platforms with GNU libiconv.
  27. `JIS_X0201`, a character set for the Japanese language.
  28. `MAC-ARABIC`, a platform specific extension of the ASCII character set.
  29. `MAC-CENTRAL-EUROPE`, a platform specific extension of the ASCII character set.
  30. `MAC-CROATIAN`, a platform specific extension of the ASCII character set.
  31. `MAC-CYRILLIC`, a platform specific extension of the ASCII character set.
  32. `MAC-DINGBAT`, a platform specific character set.
  33. `MAC-GREEK`, a platform specific extension of the ASCII character set.
  34. `MAC-HEBREW`, a platform specific extension of the ASCII character set.
  35. `MAC-ICELAND`, a platform specific extension of the ASCII character set.
  36. `MAC-ROMAN` ≡ `MACINTOSH`, a platform specific extension of the ASCII character set.
  37. `MAC-ROMANIA`, a platform specific extension of the ASCII character set.
  38. `MAC-SYMBOL`, a platform specific character set.
  39. `MAC-THAI`, a platform specific extension of the ASCII character set.
  40. `MAC-TURKISH`, a platform specific extension of the ASCII character set.
  41. `MAC-UKRAINE`, a platform specific extension of the ASCII character set.
  42. `CP437`, a DOS oldie, a platform specific extension of the ASCII character set.
  43. `CP437-IBM`, an IBM variant of `CP437`.
  44. `CP737`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for the Greek language.
  45. `CP775`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for some Baltic languages.
  46. `CP850`, a DOS oldie, a platform specific extension of the ASCII character set.
  47. `CP852`, a DOS oldie, a platform specific extension of the ASCII character set.
  48. `CP852-IBM`, an IBM variant of `CP852`.
  49. `CP855`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for the Russian language.
  50. `CP857`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for the Turkish language.
  51. `CP860`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for the Portuguese language.
  52. `CP860-IBM`, an IBM variant of `CP860`.
  53. `CP861`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for the Icelandic language.
  54. `CP861-IBM`, an IBM variant of `CP861`.
  55. `CP862`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for the Hebrew language.
  56. `CP862-IBM`, an IBM variant of `CP862`.
  57. `CP863`, a DOS oldie, a platform specific extension of the ASCII character set.
  58. `CP863-IBM`, an IBM variant of `CP863`.
  59. `CP864`, a DOS oldie, meant to be suitable for the Arabic language.
  60. `CP864-IBM`, an IBM variant of `CP864`.
  61. `CP865`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for some Nordic languages.
  62. `CP865-IBM`, an IBM variant of `CP865`.
  63. `CP866`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for the Russian language.
  64. `CP869`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for the Greek language.
  65. `CP869-IBM`, an IBM variant of `CP869`.
  66. `CP874`, a DOS oldie, a platform specific extension of the ASCII character set, meant to be suitable for the Thai language.
  67. `CP874-IBM`, an IBM variant of `CP874`.
  68. `WINDOWS-1250` ≡ `CP1250`, a platform specific extension of the ASCII character set, heavily incompatible with ISO-8859-2.
  69. `WINDOWS-1251` ≡ `CP1251`, a platform specific extension of the ASCII character set, heavily incompatible with ISO-8859-5, meant to be suitable for the Russian language.
  70. `WINDOWS-1252` ≡ `CP1252`, a platform specific extension of the ISO-8859-1 character set.
  71. `WINDOWS-1253` ≡ `CP1253`, a platform specific extension of the ASCII character set, gratuitously incompatible with ISO-8859-7, meant to be suitable for the Greek language.
  72. `WINDOWS-1254` ≡ `CP1254`, a platform specific extension of the ISO-8859-9 character set.
  73. `WINDOWS-1255` ≡ `CP1255`, a platform specific extension of the ASCII character set, gratuitously incompatible with ISO-8859-8, suitable for the Hebrew language. This character set is only available on platforms with GNU libc or GNU libiconv.
  74. `WINDOWS-1256` ≡ `CP1256`, a platform specific extension of the ASCII character set, meant to be suitable for the Arabic language.
  75. `WINDOWS-1257` ≡ `CP1257`, a platform specific extension of the ASCII character set.
  76. `WINDOWS-1258` ≡ `CP1258`, a platform specific extension of the ASCII character set, meant to be suitable for the Vietnamese language. This character set is only available on platforms with GNU libc or GNU libiconv.
  77. `HP-ROMAN8`, a platform specific extension of the ASCII character set.
  78. `NEXTSTEP`, a platform specific extension of the ASCII character set.
  79. `EUC-JP`, a multibyte character set for the Japanese language. This character set is only available on platforms with GNU libc or GNU libiconv.
  80. `SHIFT-JIS`, a multibyte character set for the Japanese language. This character set is only available on platforms with GNU libc or GNU libiconv.
  81. `CP932`, a Microsoft variant of `SHIFT-JIS`. This character set is only available on platforms with GNU libc or GNU libiconv.
  82. `ISO-2022-JP`, a stateful 7-bit multibyte character set for the Japanese language. This character set is only available on platforms with GNU libc or GNU libiconv.
  83. `ISO-2022-JP-2`, a stateful 7-bit multibyte character set for the Japanese language. This character set is only available on platforms with GNU libc 2.3 or newer or GNU libiconv.
  84. `ISO-2022-JP-1`, a stateful 7-bit multibyte character set for the Japanese language. This character set is only available on platforms with GNU libiconv.
  85. `EUC-CN`, a multibyte character set for simplified Chinese. This character set is only available on platforms with GNU libc or GNU libiconv.
  86. `HZ`, a stateful 7-bit multibyte character set for simplified Chinese. This character set is only available on platforms with GNU libiconv.
  87. `GBK`, a multibyte character set for Chinese, This character set is only available on platforms with GNU libc or GNU libiconv.
  88. `CP936`, a Microsoft variant of `GBK`. This character set is only available on platforms with GNU libc or GNU libiconv.
  89. `GB18030`, a multibyte character set for Chinese, This character set is only available on platforms with GNU libc or GNU libiconv.
  90. `EUC-TW`, a multibyte character set for traditional Chinese. This character set is only available on platforms with GNU libc or GNU libiconv.
  91. `BIG5`, a multibyte character set for traditional Chinese. This character set is only available on platforms with GNU libc or GNU libiconv.
  92. `CP950`, a Microsoft variant of `BIG5`. This character set is only available on platforms with GNU libc or GNU libiconv.
  93. `BIG5-HKSCS`, a multibyte character set for traditional Chinese. This character set is only available on platforms with GNU libc or GNU libiconv.
  94. `ISO-2022-CN`, a stateful 7-bit multibyte character set for Chinese. This character set is only available on platforms with GNU libc or GNU libiconv.
  95. `ISO-2022-CN-EXT`, a stateful 7-bit multibyte character set for Chinese. This character set is only available on platforms with GNU libc or GNU libiconv.
  96. `EUC-KR`, a multibyte character set for Korean. This character set is only available on platforms with GNU libc or GNU libiconv.
  97. `CP949`, a Microsoft variant of `EUC-KR`. This character set is only available on platforms with GNU libc or GNU libiconv.
  98. `ISO-2022-KR`, a stateful 7-bit multibyte character set for Korean. This character set is only available on platforms with GNU libc or GNU libiconv.
  99. `JOHAB`, a multibyte character set for Korean used mostly on DOS. This character set is only available on platforms with GNU libc or GNU libiconv.
  100. `ARMSCII-8`, an extension of the ASCII character set, suitable for the Armenian. This character set is only available on platforms with GNU libc or GNU libiconv.
  101. `GEORGIAN-ACADEMY`, an extension of the ASCII character set, suitable for the Georgian. This character set is only available on platforms with GNU libc or GNU libiconv.
  102. `GEORGIAN-PS`, an extension of the ASCII character set, suitable for the Georgian. This character set is only available on platforms with GNU libc or GNU libiconv.
  103. `TIS-620`, an extension of the ASCII character set, suitable for the Thai. This character set is only available on platforms with GNU libc or GNU libiconv.
  104. `MULELAO-1`, an extension of the ASCII character set, suitable for the Laotian. This character set is only available on platforms with GNU libiconv.
  105. `CP1133`, an extension of the ASCII character set, suitable for the Laotian. This character set is only available on platforms with GNU libc or GNU libiconv.
  106. `VISCII`, an extension of the ASCII character set, suitable for the Vietnamese. This character set is only available on platforms with GNU libc or GNU libiconv.
  107. `TCVN`, an extension of the ASCII character set, suitable for the Vietnamese. This character set is only available on platforms with GNU libc or GNU libiconv.

  108. `BASE64`, encodes arbitrary byte sequences with 64 ASCII characters

       ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/

       as specifined by `MIME`; 3 bytes are encoded with 4 characters, line breaks are inserted after every 76 characters.

       While this is not a traditional character set (i.e., it does not map a set of characters in a natural language into bytes), it does define a map between arbitrary byte sequences and certain character sequences, so it falls naturally into the `EXT:ENCODING` class.

  Platform Dependent: Only on GNU systems with GNU libc 2.2 or better and other systems (UNIX and Win32) on which the GNU libiconv C library has been installed

    The character sets provided by the library function `iconv` can also be used as encodings. To create such an encoding, call `EXT:MAKE-ENCODING` with the character set name (a string) as the `:CHARSET` argument.

    When an `EXT:ENCODING` is available both as a built-in and through `iconv`, the built-in is used, because it is more efficient and available across all platforms.

    These encodings are not assigned to global variables, since there is no portable way to get the list of all character sets supported by `iconv`.

    On standard-compliant UNIX systems (e.g., GNU systems, such as GNU/Linux and GNU/Hurd) and on systems with GNU libiconv you get this list by calling the program: iconv -l.

    The reason we use only GNU libc 2.2 or GNU libiconv is that the other `iconv` implementations are broken in various ways and we do not want to deal with random CLISP crashes caused by those bugs. If your system supplies an `iconv` implementation which passes the GNU libiconv's test suite, please report that to clisp-list and a future CLISP version will use `iconv` on your system.

### 31.5.3. Line Terminators

The line terminator mode can be one of the following three keywords:

`:UNIX`
  Newline is represented by the ASCII LF character (U000A).
`:MAC`
  Newline is represented by the ASCII CR character (U000D).
`:DOS`
  Newline is represented by the ASCII CR followed by the ASCII LF.

Windows programs typically use the `:DOS` line terminator, sometimes they also accept `:UNIX` line terminators or produce `:MAC` line terminators.

The HTTP protocol also requires `:DOS` line terminators.

The line terminator mode is relevant only for output (writing to a file/pipe/socket `STREAM`). During input, all three kinds of line terminators are recognized. See also Section 13.11, “Treatment of Newline during Input and Output sec_13-1-8”.

### 31.5.4. Function `EXT:MAKE-ENCODING`

The function `(`EXT:MAKE-ENCODING` `&KEY` :CHARSET :LINE-TERMINATOR :INPUT-ERROR-ACTION :OUTPUT-ERROR-ACTION)` returns an `EXT:ENCODING`. The `:CHARSET` argument may be an encoding, a string, or `:DEFAULT`. The possible values for the line terminator argument are the keywords `:UNIX`, `:MAC`, `:DOS`.

The `:INPUT-ERROR-ACTION` argument specifies what happens when an invalid byte sequence is encountered while converting bytes to characters. Its value can be `:ERROR`, `:IGNORE` or a character to be used instead. The UNICODE character #\uFFFD is typically used to indicate an error in the input sequence.

The `:OUTPUT-ERROR-ACTION` argument specifies what happens when an invalid character is encountered while converting characters to bytes. Its value can be `:ERROR`, `:IGNORE`, a byte to be used instead, or a character to be used instead. The UNICODE character #\uFFFD can be used here only if it is encodable in the character set.

### 31.5.5. Function `EXT:ENCODING-CHARSET`

#### Platform Dependent: Only in CLISP built with compile-time flag UNICODE

The function `(`EXT:ENCODING-CHARSET` `encoding`)` returns the charset of the `encoding`, as a `SYMBOL` or a `STRING`.

### Warning

`(`STRING` (`EXT:ENCODING-CHARSET` `encoding`))` is not necessarily a valid `MIME` name.

### 31.5.6. Default encodings

Besides every file/pipe/socket `STREAM` containing an encoding, the following `SYMBOL-MACRO` places contain global `EXT:ENCODING`s:

`SYMBOL-MACRO` `CUSTOM:*DEFAULT-FILE-ENCODING*`. The `SYMBOL-MACRO` place `CUSTOM:*DEFAULT-FILE-ENCODING*` is the encoding used for new file/pipe/socket `STREAM`, when no `:EXTERNAL-FORMAT` argument was specified.

Platform Dependent: Only in CLISP built with compile-time flag UNICODE

  The following are `SYMBOL-MACRO` places.

  `CUSTOM:*PATHNAME-ENCODING*`

    is the encoding used for converting filenames in the file system (represented with byte sequences by the OS) to lisp `PATHNAME` components (`STRING`s). If this encoding is incompatible with some file names on your system, file system access (e.g., `DIRECTORY`) may `SIGNAL` `ERROR`s, thus extreme caution is recommended if this is not a “1:1” encoding. Sometimes it may not be obvious that the encoding is involved at all. E.g., on Win32:

        (PARSE-NAMESTRING (STRING #\ARMENIAN_SMALL_LETTER_RA))
        *** - PARSE-NAMESTRING: syntax error in filename "ռ" at position 0

    when `CUSTOM:*PATHNAME-ENCODING*` is `CHARSET:UTF-16` because then `#\ARMENIAN_SMALL_LETTER_RA` corresponds to the 4 bytes `#(255 254 124 5)` and the byte `124` is not a valid byte for a Win32 file name because it means `|` in ASCII.

    The set of valid pathname bytes is determined by the GNU autoconf test `src/m4/filecharset.m4` at configure time. While rather stable for the first 127 bytes, on Win32 it varies wildly for the bytes 128-256, depending on the OS version and the file system.

    The line terminator mode of `CUSTOM:*PATHNAME-ENCODING*` is ignored.

    Platform Dependent: Mac OS X platform only: Mac OS X pathnames are actually UNICODE `STRING`s, so `CUSTOM:*PATHNAME-ENCODING*` is a constant with value `CHARSET:UTF-8`.

  `CUSTOM:*TERMINAL-ENCODING*`
    is the encoding used for communication with the terminal, in particular by `*TERMINAL-IO*`.
  `CUSTOM:*MISC-ENCODING*`
    is the encoding used for access to environment variables, command line options, and the like. Its line terminator mode is ignored.
  `CUSTOM:*FOREIGN-ENCODING*`
    is the encoding for strings passed through the “FFI” (some platforms only). If it is a “1:1” encoding, i.e. an encoding in which every character is represented by one byte, it is also used for passing characters through the “FFI”.

The default encoding objects are initialized according to ``-E`domain` `encoding```.

### Reminder

You have to use `EXT:LETF`/`EXT:LETF*` for `SYMBOL-MACRO`s; `LET`/`LET*` will not work!

#### 31.5.6.1. Default line terminator

The line terminator facet of the above `EXT:ENCODING`s is determined by the following logic: since CLISP understands all possible line terminators on input (see Section 13.11, “Treatment of Newline during Input and Output sec_13-1-8”), all that matters is what line terminator do most other programs expect?

Platform Dependent: UNIX platform only.
  If a non-0 `O_BINARY` cpp constant is defined, we assume that the OS distinguishes between text and binary files, and, since the encodings are relevant only for text files, we thus use `:DOS`; otherwise the default is `:UNIX`.
Platform Dependent: Win32 platform only.
  Since most Win32 programs expect CRLF, the default line terminator is `:DOS`.

This boils down to the following code in `src/encoding.d`:

     #if defined(WIN32) || (defined(UNIX) && (O_BINARY != 0))

### Default line terminator on Cygwin

Both of the above tests pass on Cygwin, so the default line terminator is `:DOS`. If you so desire, you can change it in your RC file.

### 31.5.7. Converting between strings and byte vectors

Encodings can also be used to convert directly between strings and their corresponding byte vector representation according to that encoding.

`(`EXT:CONVERT-STRING-FROM-BYTES` `vector` `encoding` `&KEY` `:START` `:END`)`
  converts the subsequence of `vector` (a `(`VECTOR` (`UNSIGNED-BYTE` 8))`) from `start` to `end` to a `STRING`, according to the given `encoding`, and returns the resulting string.
`(`EXT:CONVERT-STRING-TO-BYTES` `string` `encoding` `&KEY` `:START` `:END`)`
  converts the subsequence of `string` from `start` to `end` to a `(`VECTOR` (`UNSIGNED-BYTE` 8))`, according to the given `encoding`, and returns the resulting byte vector.

## 31.6. Generic streams

This interface is CLISP-specific and now obsolete. Please use the Gray streams interface instead.

Generic streams are user programmable streams. The programmer interface:

`(`gstream:make-generic-stream` `controller`)`
  returns a generic stream.
`(`gstream:generic-stream-controller` `stream`)`
  returns a private object to which generic stream methods dispatch. The typical usage is to retrieve the object originally provided by the user in `gstream:make-generic-stream`.
`(`gstream:generic-stream-p` `stream`)`
  determines whether a stream is a generic stream, returning `T` if it is, `NIL` otherwise.

In order to specify the behavior of a generic stream, the user must define CLOS methods on the following CLOS generic functions. The function `gstream:generic-stream-`x`` corresponds to the Common Lisp function ``x``. They all take a controller and some number of arguments.

`(gstream:generic-stream-read-char `controller`)`
  Returns and consumes the next character, `NIL` at end of file. Takes one argument, the controller object.
`(gstream:generic-stream-peek-char `controller`)`
  Returns the next character, `NIL` at end of file. A second value indicates whether the side effects associated with consuming the character were executed: `T` means that a full `READ-CHAR` was done, `NIL` means that no side effects were done. Takes one argument, the controller object.
`(gstream:generic-stream-read-byte `controller`)`
  Returns and consumes the next integer, `NIL` at end of file. Takes one argument, the controller object.
`(gstream:generic-stream-read-char-will-hang-p `controller`)`
  This generic function is used to query the stream's input status. It returns `NIL` if `gstream:generic-stream-read-char` and `gstream:generic-stream-peek-char` will certainly return immediately. Otherwise it returns true.
`(gstream:generic-stream-write-char `controller` `char`)`
  The first argument is the controller object. The second argument is the character to be written.
`(gstream:generic-stream-write-byte `controller` `by`)`
  The first argument is the controller object. The second argument is the integer to be written.
`(gstream:generic-stream-write-string `controller` `string` `start` `length`)`
  Writes the subsequence of `string` starting from `start` of length `length`. The first argument is the controller object.
`(gstream:generic-stream-clear-input `controller`)`
`(gstream:generic-stream-clear-output `controller`)`
`(gstream:generic-stream-finish-output `controller`)`
`(gstream:generic-stream-force-output `controller`)`
`(gstream:generic-stream-close `controller`)`
  Take one argument, the controller object.

## 31.7. Weak Objects

Recall two terms: An object is called “"alive"” as long as it can be retrieved by the user or program, through any kind of references, starting from global and local variables. (Objects that consume no heap storage, also known as “"immediate objects"”, such as `CHARACTER`s, `FIXNUM`s, and `SHORT-FLOAT`s, are alive indefinitely.) An object is said to be garbage-collected when its storage is reclaimed, at some moment after it becomes “"dead"”.

### 31.7.1. Weak Pointers

A `EXT:WEAK-POINTER` is an object holding a reference to a given object, without keeping the latter from being garbage-collected.

Weak Pointer API

`(`EXT:MAKE-WEAK-POINTER` `value`)`
  returns a fresh `EXT:WEAK-POINTER` referring to `value`.
`(`EXT:WEAK-POINTER-P` `object`)`
  returns true if the `object` is of type `EXT:WEAK-POINTER`.
`(`EXT:WEAK-POINTER-VALUE` `weak-pointer`)`
  returns two values: The original value and `T`, if the value has not yet been garbage-collected, else `NIL` and `NIL`. It is `SETF`-able: you can change the value that the weak pointer points to.

Weak pointers are useful for notification-based communication protocols between software modules, e.g. when a change to an object `x` requires a notification to an object `y`, as long as `y` is alive.

### 31.7.2. Weak Lists

A `EXT:WEAK-LIST` is an ordered collection of references to objects that does not keep the objects from being garbage-collected. It is semantically equivalent to a list of `EXT:WEAK-POINTER`s, however with a more efficient in-memory representation than a plain list of `EXT:WEAK-POINTER`s would be.

Weak List API

`(`EXT:MAKE-WEAK-LIST` `list`)`
  creates a `EXT:WEAK-LIST` pointing to each of the elements in the given `list`.
`(`EXT:WEAK-LIST-P` `object`)`
  returns true if the `object` is of type `EXT:WEAK-LIST`.
`(`EXT:WEAK-LIST-LIST` `weak-list`)`
  returns a `LIST` of those objects from the `weak-list` that are still alive.
`(`SETF` (`EXT:WEAK-LIST-LIST` `weak-list`) `list`)`
  replaces the list of objects stored by the `weak-list`.

Weak lists are useful for notification based communication protocols between software modules, e.g. when a change to an object `x` requires a notification to objects `k1`, `k2`, ..., as long as such a particular `kn` is alive.

A `EXT:WEAK-LIST` with a single element is semantically equivalent to a single `EXT:WEAK-POINTER`.

### 31.7.3. Weak “And” Relations

A weak “and” relation is an ordered collection of references to objects, that does not keep the objects from being garbage-collected, and which allows access to all the objects as long as all of them are still alive. As soon as one of them is garbage-collected, the entire collection of objects becomes empty.

Weak “And” Relation API

`(`EXT:MAKE-WEAK-AND-RELATION` `list`)`
  creates a `EXT:WEAK-AND-RELATION` between the objects in the given `list`.
`(`EXT:WEAK-AND-RELATION-P` `object`)`
  returns true if the `object` is of type `EXT:WEAK-AND-RELATION`.
`(`EXT:WEAK-AND-RELATION-LIST` `weak-and-relation`)`
  returns the list of objects stored in the `weak-and-relation`. The returned list must not be destructively modified.

`EXT:WEAK-AND-RELATION`s are useful to model relations between objects that become worthless when one of the objects dies.

A `EXT:WEAK-AND-RELATION` with a single element is semantically equivalent to a `EXT:WEAK-POINTER`.

### 31.7.4. Weak “Or” Relations

A weak “or” relation is an ordered collection of references to objects, that keeps all objects from being garbage-collected as long as one of them is still alive. In other words, each of them keeps all others among them from being garbage-collected. When all of them are unreferenced, the collection of objects becomes empty.

Weak “Or” Relation API

`(`EXT:MAKE-WEAK-OR-RELATION` `list`)`
  creates a `EXT:WEAK-OR-RELATION` between the objects in the given `list`.
`(`EXT:WEAK-OR-RELATION-P` `object`)`
  returns true if the `object` is of type `EXT:WEAK-OR-RELATION`.
`(`EXT:WEAK-OR-RELATION-LIST` `weak-or-relation`)`
  returns the list of objects stored in the `weak-or-relation`. The returned list must not be destructively modified.

`EXT:WEAK-OR-RELATION`s are useful to model relations between objects that do not become worthless when one of the objects dies.

A `EXT:WEAK-OR-RELATION` with a single element is semantically equivalent to a `EXT:WEAK-POINTER`.

### 31.7.5. Weak Associations

A weak association is a mapping from an object called `key` to an object called `value`, that exists as long as the key is alive. In other words, as long as the key is alive, it keeps the value from being garbage-collected.

Weak Association API

`(`EXT:MAKE-WEAK-MAPPING` `key` `value`)`
  creates a `EXT:WEAK-MAPPING`.
`(`EXT:WEAK-MAPPING-P` `object`)`
  returns true if the object is of type `EXT:WEAK-MAPPING`.
`(`EXT:WEAK-MAPPING-PAIR` `weak-mapping`)`
  returns three values: the original key, the original value, and `T`, if the key has not yet been garbage-collected, else `NIL`, `NIL`, `NIL`.
`(`EXT:WEAK-MAPPING-VALUE` `weak-mapping`)`
  returns the value, if the key has not yet been garbage-collected, else `NIL`.
`(`SETF` (`EXT:WEAK-MAPPING-VALUE` `weak-mapping`) `value`)`
  replaces the value stored in the `weak-mapping`. It has no effect when the key has already been garbage-collected.

Weak associations are useful to supplement objects with additional information that is stored outside of the object.

### 31.7.6. Weak “And” Mappings

A weak “and” mapping is a mapping from a tuple of objects called `keys` to an object called `value`, that does not keep the keys from being garbage-collected and that exists as long as all keys are alive. As soon as one of the keys is garbage-collected, the entire mapping goes away.

Weak “And” Mapping API

`(`EXT:MAKE-WEAK-AND-MAPPING` `keys` `value`)`
  creates a `EXT:WEAK-AND-MAPPING` between the `keys` objects in the given list and the given `value`. The `keys` list must be non-empty.
`(`EXT:WEAK-AND-MAPPING-P` `object`)`
  returns true if the `object` is of type `EXT:WEAK-AND-MAPPING`.
`(`EXT:WEAK-AND-MAPPING-PAIR` `weak-and-mapping`)`
  returns three values: the list of keys, the value, and `T`, if none of the keys have been garbage-collected, else `NIL`, `NIL`, `NIL`. The returned keys list must not be destructively modified.
`(`EXT:WEAK-AND-MAPPING-VALUE` `weak-and-mapping`)`
  returns the value, if none of the keys have been garbage-collected, else `NIL`.
`(`SETF` (`EXT:WEAK-AND-MAPPING-VALUE` `weak-and-mapping`) `value`)`
  replaces the value stored in the `weak-and-mapping`. It has no effect when some key has already been garbage-collected.

`EXT:WEAK-AND-MAPPING`s are useful to model properties of sets of objects that become worthless when one of the objects dies.

A `EXT:WEAK-AND-MAPPING` with a single key is semantically equivalent to a weak association.

### 31.7.7. Weak “Or” Mappings

A weak “or” mapping is a mapping from a tuple of objects called `keys` to an object called `value`, that keeps all keys and the value from being garbage-collected as long as one of the keys is still alive. In other words, each of the keys keeps all others among them and the value from being garbage-collected. When all of them are unreferenced, the entire mapping goes away.

Weak “Or” Mapping API

`(`EXT:MAKE-WEAK-OR-MAPPING` `keys` `value`)`
  creates a `EXT:WEAK-OR-MAPPING` between the `keys` objects in the given list and the given `value`. The `keys` list must be non-empty.
`(`EXT:WEAK-OR-MAPPING-P` `object`)`
  returns true if the `object` is of type `EXT:WEAK-OR-MAPPING`.
`(`EXT:WEAK-OR-MAPPING-PAIR` `weak-or-mapping`)`
  returns three values: the list of keys, the value, and `T`, if the keys have not yet been garbage-collected, else `NIL`, `NIL`, `NIL`. The returned keys list must not be destructively modified.
`(`EXT:WEAK-OR-MAPPING-VALUE` `weak-or-mapping`)`
  returns the value, if the keys have not yet been garbage-collected, else `NIL`.
`(`SETF` (`EXT:WEAK-OR-MAPPING-VALUE` `weak-or-mapping`) `value`)`
  replaces the value stored in the `weak-or-mapping`. It has no effect when the keys have already been garbage-collected.

`EXT:WEAK-OR-MAPPING`s are useful to model properties of sets of objects that do not become worthless when one of the objects dies.

A `EXT:WEAK-OR-MAPPING` with a single key is semantically equivalent to a weak association.

### 31.7.8. Weak Association Lists

A weak association list is an ordered collection of pairs, each pair being built from an object called `key` and an object called `value`. The lifetime of each pair depends on the type of the weak association list:

`:KEY`
  The pair exists as long as the `key` is not garbage-collected. As long as the `key` is alive, it prevents the `value` from being garbage-collected.
`:VALUE`
  The pair exists as long as the `value` is not garbage-collected. As long as the `value` is alive, it prevents the `key` from being garbage-collected.
`:KEY-AND-VALUE`
  The pair exists as long as the `key` and the `value` are alive.
`:KEY-OR-VALUE`
  The pair exists as long as the `key` or the `value` are alive. As long as the `key` is alive, it prevents the `value` from being garbage-collected, and as long as the `value` is alive, it prevents the `key` from being garbage-collected.

In other words, each pair is:

`:KEY`
  a `EXT:WEAK-MAPPING` from the `key` to the `value`,
`:VALUE`
  a `EXT:WEAK-MAPPING` from the `value` to the `key`,
`:KEY-AND-VALUE`
  a `EXT:WEAK-AND-RELATION` of the `key` and the `value`,
`:KEY-OR-VALUE`
  a `EXT:WEAK-OR-RELATION` of the `key` and the `value`.

Weak Association List API

`(`EXT:MAKE-WEAK-ALIST` :type :initial-contents)`
  creates a `EXT:WEAK-ALIST`. The `type` argument must be one of the four aforementioned types; the default is `:KEY`. The `initial-contents` argument must be an association list.
`(`EXT:WEAK-ALIST-P` `object`)`
  returns true if the `object` is of type `EXT:WEAK-ALIST`.
`(`EXT:WEAK-ALIST-TYPE` `weak-alist`)`
  returns the type of the `weak-alist`.
`(`EXT:WEAK-ALIST-CONTENTS` `weak-alist`)`
  returns an association list that corresponds to the current contents of the `weak-alist`.
`(`SETF` (`EXT:WEAK-ALIST-CONTENTS` `weak-alist`) `contents`)`
  replaces the contents of a `weak-alist`. The `contents` argument must be an association list.
`(`EXT:WEAK-ALIST-ASSOC` `item` `weak-alist` [:test] [:test-not] [:key])`
  is equivalent to `(`ASSOC` `item` (`EXT:WEAK-ALIST-CONTENTS` `weak-alist`) [:test] [:test-not] [:key])`.
`(`EXT:WEAK-ALIST-RASSOC` `item` `weak-alist` [:test] [:test-not] [:key])`
  is equivalent to `(`RASSOC` `item` (`EXT:WEAK-ALIST-CONTENTS` `weak-alist`) [:test] [:test-not] [:key])`.
`(`EXT:WEAK-ALIST-VALUE` `item` `weak-alist` [:test] [:test-not])`
  is equivalent to `(`CDR` (`EXT:WEAK-LIST-ASSOC` `item` `weak-alist` [:test] [:test-not]))`.
`(`SETF` (`EXT:WEAK-ALIST-VALUE` `item` `weak-alist` [:test] [:test-not]) `value`)`
  replaces the value stored for `item` in a `weak-alist`. When a pair with the given `item` as key does not exist or has already been garbage-collected, a new pair is added to the association list.

Weak associations lists are useful to supplement objects with additional information that is stored outside of the object, when the number of such objects is known to be small.

### 31.7.9. Weak Hash Tables

A weak `HASH-TABLE` is an unordered collection of pairs, each pair being built from an object called `key` and an object called `value`. There can be only one pair with a given `key` in a weak `HASH-TABLE`. The lifetime of each pair depends on the type of the weak `HASH-TABLE`

`:KEY`
  The pair exists as long as the `key` is not garbage-collected. As long as the `key` is alive, it prevents the `value` from being garbage-collected.
`:VALUE`
  The pair exists as long as the `value` is not garbage-collected. As long as the `value` is alive, it prevents the `key` from being garbage-collected.
`:KEY-AND-VALUE`
  The pair exists as long as the `key` and the `value` are alive.
`:KEY-OR-VALUE`
  The pair exists as long as the `key` or the `value` are alive. As long as the `key` is alive, it prevents the `key` from being garbage-collected, and as long as the `value` is alive, it prevents the `key` from being garbage-collected.

In other words, each pair is:

`:KEY`
  a `EXT:WEAK-MAPPING` from the `key` to the `value`,
`:VALUE`
  a `EXT:WEAK-MAPPING` from the `value` to the `key`,
`:KEY-AND-VALUE`
  a `EXT:WEAK-AND-RELATION` of the `key` and the `value`,
`:KEY-OR-VALUE`
  a `EXT:WEAK-OR-RELATION` of the `key` and the `value`.

See also Section 18.2, “Function `MAKE-HASH-TABLE`”.

Weak `HASH-TABLE`s are useful to supplement objects with additional information that is stored outside of the object. This data structure scales up without performance degradation when the number of pairs is big.

Weak `HASH-TABLE`s are also useful to implement canonicalization tables.

## 31.8. Finalization

Calling `(`EXT:FINALIZE` `object` `function`)` has the effect that when the specified object is being garbage-collected, `(`FUNCALL` `function` `object`)` will be executed.

Calling `(`EXT:FINALIZE` `object` `function` `guardian`)` has a similar effect, but only as long as the `guardian` has not been garbage-collected: when `object` is being garbage-collected, `(`FUNCALL` `function` `object` `guardian`)` will be executed. If the `guardian` is garbage-collected before `object` is, nothing happens.

### Note

The time when “the `object` is being garbage-collected” is not defined deterministically. (Actually, it might possibly never occur.) It denotes a moment at which no references to `object` exist from other Lisp objects. When the `function` is called, `object` (and, possibly, `guardian`) enter the “arena of live Lisp objects” again.

No finalization request will be executed more than once.

## 31.9. The Prompt

CLISP prompt consists of 3 mandatory parts: “start”, “body”, and “finish”; and 2 optional parts: “break”, which appears only in the debugger (after `BREAK` or `ERROR`), and “step”, which appears only in the `STEP`er. Each part is controlled by a custom variable, which can be either a `STRING` or a `FUNCTION` of no arguments returning a `STRING` (if it is something else - or if the return value was not a `STRING` - it is printed with `PRINC`). In the order of invocation:

`CUSTOM:*PROMPT-START*`
  Defaults to an empty string.
`CUSTOM:*PROMPT-STEP*`
  Used only during `STEP`ping. Defaults to “`Step n` ”, where `n` is the stepping level as returned by `EXT:STEP-LEVEL`.
`CUSTOM:*PROMPT-BREAK*`
  Used only inside break loop (during debugging). Defaults to “`Break n` ”, where `n` is the break level as returned by `EXT:BREAK-LEVEL`.
`CUSTOM:*PROMPT-BODY*`
  Defaults to “`package[n]`” where `package` is the shortest (nick)name (as returned by `EXT:PACKAGE-SHORTEST-NAME`) of the current package `*PACKAGE*` if it is not the same as it was in the beginning (determined by `EXT:PROMPT-NEW-PACKAGE`) or if it does not contain symbol `T`, (it is assumed that in the latter case you would want to keep in mind that your current package is something weird); and `n` is the index of the current prompt, kept in `EXT:*COMMAND-INDEX*`.
`CUSTOM:*PROMPT-FINISH*`
  Defaults to “`>` ”.

To facilitate your own custom prompt creation, the following functions and variables are available:

`EXT:BREAK-LEVEL`
  This `FUNCTION` returns current `BREAK`/`ERROR` level.
`EXT:STEP-LEVEL`
  This `FUNCTION` returns current `STEP` level.
`EXT:PROMPT-NEW-PACKAGE`
  This `FUNCTION` returns `*PACKAGE*` or `NIL` if the current package is the same as it was initially.
`EXT:PACKAGE-SHORTEST-NAME`
  This `FUNCTION` takes one argument, a `PACKAGE`, and returns its shortest name or nickname.
`EXT:*COMMAND-INDEX*`
  contains the current prompt number; it is your responsibility to increment it (this variable is bound to 0 before saving the memory image).

## 31.10. Maximum ANSI CL compliance

Some [ANSI CL standard] features are turned off by default for convenience and backward compatibility. They can be switched on, all at once, by setting the `SYMBOL-MACRO` `CUSTOM:*ANSI*` to `T`, or they can be switched on individually. Setting `CUSTOM:*ANSI*` to `T` implies the following:

1. Setting `CUSTOM:*PRINT-PATHNAMES-ANSI*` to `T`.
2. Setting `CUSTOM:*PRINT-SPACE-CHAR-ANSI*` to `T`.
3. Setting `CUSTOM:*COERCE-FIXNUM-CHAR-ANSI*` to `T`.
4. Setting `CUSTOM:*SEQUENCE-COUNT-ANSI*` to `T`.
5. Setting `CUSTOM:*MERGE-PATHNAMES-ANSI*` to `T`.
6. Setting `CUSTOM:*PARSE-NAMESTRING-ANSI*` to `T`.
7. Setting `CUSTOM:*FLOATING-POINT-CONTAGION-ANSI*` to `T`.
8. Setting `CUSTOM:*FLOATING-POINT-RATIONAL-CONTAGION-ANSI*` to `T`.
9. Setting `CUSTOM:*PHASE-ANSI*` to `T`.
10. Setting `CUSTOM:*LOOP-ANSI*` to `T`.
11. Setting `CUSTOM:*PRINT-EMPTY-ARRAYS-ANSI*` to `T`.
12. Setting `CUSTOM:*PRINT-UNREADABLE-ANSI*` to `T`.
13. Setting `CUSTOM:*DEFUN-ACCEPT-SPECIALIZED-LAMBDA-LIST*` to `NIL`.

### Note

If you run CLISP with the `-ansi` switch or set the `SYMBOL-MACRO` `CUSTOM:*ANSI*` to `T` and then save memory image, then all subsequent invocations of CLISP with this image will be as if with `-ansi` (regardless whether you actually supply the `-ansi` switch). You can always set the `SYMBOL-MACRO` `CUSTOM:*ANSI*` to `NIL`, or invoke CLISP with the `-traditional` switch, reversing the above settings, i.e.,

1. Setting `CUSTOM:*PRINT-PATHNAMES-ANSI*` to `NIL`.
2. Setting `CUSTOM:*PRINT-SPACE-CHAR-ANSI*` to `NIL`.
3. Setting `CUSTOM:*COERCE-FIXNUM-CHAR-ANSI*` to `NIL`.
4. Setting `CUSTOM:*SEQUENCE-COUNT-ANSI*` to `NIL`.
5. Setting `CUSTOM:*MERGE-PATHNAMES-ANSI*` to `NIL`.
6. Setting `CUSTOM:*PARSE-NAMESTRING-ANSI*` to `NIL`.
7. Setting `CUSTOM:*FLOATING-POINT-CONTAGION-ANSI*` to `NIL`.
8. Setting `CUSTOM:*FLOATING-POINT-RATIONAL-CONTAGION-ANSI*` to `NIL`.
9. Setting `CUSTOM:*PHASE-ANSI*` to `NIL`.
10. Setting `CUSTOM:*LOOP-ANSI*` to `NIL`.
11. Setting `CUSTOM:*PRINT-EMPTY-ARRAYS-ANSI*` to `NIL`.
12. Setting `CUSTOM:*PRINT-UNREADABLE-ANSI*` to `NIL`.
13. Setting `CUSTOM:*DEFUN-ACCEPT-SPECIALIZED-LAMBDA-LIST*` to `T`.

## 31.11. Additional Fancy Macros and Functions

CLISP comes with some extension macros, mostly defined in the file `macros3.lisp` and loaded from the file `init.lisp` during make:

### 31.11.1. Macro `EXT:ETHE`

`(`EXT:ETHE` `value-type` `form`)` enforces a type check in both interpreted and compiled code.

### 31.11.2. Macros `EXT:LETF` & `EXT:LETF*`

These macros are similar to `LET` and `LET*`, respectively, except that they can bind places, even places with multiple values. Example:

    (letf (((values a b) form)) ...)

is equivalent to

    (multiple-value-bind (a b) form ...)

while

    (letf (((first l) 7)) ...)

is approximately equivalent to

     (LET* ((#:g1 l) (#:g2 (first #:g1)))
       (UNWIND-PROTECT (PROGN (SETF (first #:g1) 7) ...)
          (SETF (first #:g1) #:g2)))

### 31.11.3. Macro `EXT:MEMOIZED`

`(`EXT:MEMOIZED` `form`)` memoizes the primary value of `form` from its first evaluation.

### 31.11.4. Macro `EXT:WITH-COLLECT`

Similar to the `LOOP`'s `COLLECT` construct, except that it is looks more "Lispy" and can appear arbitrarily deep. It defines local macros (with `MACROLET`) which collect objects given to it into lists, which are then returned as multiple values. E.g.,

    (ext:with-collect (c0 c1)
      (dotimes (i 10) (if (oddp i) (c0 i) (c1 i))))
    ⇒ (1 3 5 7 9) ;
    ⇒ (0 2 4 6 8)

returns two `LIST`s as multiple values.

### 31.11.5. Macro `EXT:COMPILE-TIME-VALUE`

Sometimes one may want to call an expensive function at compilation time and write the primary value into the `#P".fas"` file, thus speeding up loading the `#P".fas"` file. E.g., let your file `primes.lisp` be

    (defun primes-list (limit)
      "Return the list of all primes smaller than LIMIT."
      ...)
    (defvar *all-primes* (compile-time-value (primes-list MOST-POSITIVE-FIXNUM)))

Then

`(`LOAD` "primes.lisp")`
  will not call `primes-list` and `*all-primes*` will be `NIL`.
`(`COMPILE-FILE` "primes.lisp")`
  will call `primes-list` (and will probably take a long time) and will write the resulting list into `(`COMPILE-FILE-PATHNAME` "primes.lisp")`
`(`LOAD` (`COMPILE-FILE-PATHNAME` "primes.lisp"))`
  will not call `primes-list` but `*all-primes*` will be the list computed during compilation.

An alternative is to save a memory image, which is faster than `#P".fas"` file but less portable.

### 31.11.6. Macro `EXT:WITH-GENSYMS`

Similar to its namesake from Paul Graham's book “On Lisp”, this macro is useful for writing other macros:

    (with-gensyms ("FOO-" bar baz zot) ...)

expands to

    (let ((bar (gensym "FOO-BAR-"))
          (baz (gensym "FOO-BAZ-"))
          (zot (gensym "FOO-ZOT-")))
      ...)

### 31.11.7. Function `EXT:REMOVE-PLIST`

Similar to `REMOVE` and `REMF`, this function removes some properties from a property list. It is non-destructive and thus can be used on `&REST` arguments to remove some keyword parameters, e.g.,

    (defmacro with-foo ((&KEY foo1 foo2) &BODY body)
      `(... ,foo1 ... ,foo2 ... ,@body))
    (defmacro with-foo-bar ((&REST opts &KEY bar1 bar2
                             &ALLOW-OTHER-KEYS)
                            &BODY body)
      `(with-foo (,@(remove-plist opts :bar1 :bar2)
         ... ,bar1 ... ,bar2 ... ,@body)))
    (defun foo-bar ()
      (with-foo-bar (:bar1 1 :foo2 2) ...))

here `WITH-FOO` does not receive the `:BAR1 1` argument from `FOO-BAR`.

### 31.11.8. Macros `EXT:WITH-HTML-OUTPUT` and `EXT:WITH-HTTP-OUTPUT`

Defined in `inspect.lisp`, these macros are useful for the rudimentary HTTP server defined there.

### 31.11.9. Function `EXT:OPEN-HTTP` and macro `EXT:WITH-HTTP-INPUT`

Defined in `clhs.lisp`, they allow downloading data over the Internet using the HTTP protocol. `(`EXT:OPEN-HTTP` url `&KEY` `:IF-DOES-NOT-EXIST` :LOG)` opens a socket connection to the `url` host, sends the GET request, and returns two values: the `SOCKET:SOCKET-STREAM` and content length. `(EXT:WITH-HTTP-INPUT (`variable` url) `&BODY` body)` binds `variable` to the `SOCKET:SOCKET-STREAM` returned by `EXT:OPEN-HTTP` and executes the `body`. `(EXT:WITH-HTTP-INPUT ((`variable` `contents`) url) `&BODY` body)` additionally binds `contents` to the content length.

`EXT:OPEN-HTTP` will check `CUSTOM:*HTTP-PROXY*` on startup and parse the environment variable `HTTP_PROXY` if `CUSTOM:*HTTP-PROXY*` is `NIL`.

The `:LOG` argument binds `CUSTOM:*HTTP-LOG-STREAM*`.

### 31.11.10. Variable `CUSTOM:*HTTP-LOG-STREAM*`

Function `EXT:OPEN-HTTP` logs its actions to `CUSTOM:*HTTP-LOG-STREAM*` which is initially set to `*TERMINAL-IO*`.

### 31.11.11. Function `EXT:BROWSE-URL`

Function `(`EXT:BROWSE-URL` url `&KEY` `:BROWSER` `:OUT`)` calls a browser on the URL. `browser` (defaults to `CUSTOM:*BROWSER*`) should be a valid keyword in the `CUSTOM:*BROWSERS*` association list. `:OUT` specifies the stream where the progress messages are printed (defaults to `*STANDARD-OUTPUT*`).

### 31.11.12. Variable `CUSTOM:*HTTP-PROXY*`

If you are behind a proxy server, you will need to set `CUSTOM:*HTTP-PROXY*` to a `LIST` `(name:password host port)`. By default, the environment variable `http_proxy` is used, the expected format is `"name:password@host:port"`. If no `#\@` is present, `name` and `password` are `NIL`. If no `#\:` is present, `password` (or `port`) is `NIL`.

Use function `(EXT:HTTP-PROXY `&OPTIONAL` (`STRING` (`EXT:GETENV` "http_proxy")))` to reset `CUSTOM:*HTTP-PROXY*`.

### 31.11.13. Function `EXT:CANONICALIZE`

If you want to canonicalize a `value` before further processing it, you can pass it to `EXT:CANONICALIZE` together with a `SEQUENCE` of `FUNCTION`s: `(`EXT:CANONICALIZE` `value` `functions` `&KEY` (test '`EQL`) (max-iter 1024))` will call `function`s on `value` until it stabilizes under `test` (which should be a valid `HASH-TABLE-TEST`) and return the stabilized value and the number of iterations the stabilization required.

E.g., `clx/new-clx` uses it together with `XLIB:*CANONICALIZE-ENCODING*` to fix the broken encoding names returned by the X Window System (e.g., convert `"iso8859-1"` to `"ISO-8859-1"`) before passing them over to `EXT:MAKE-ENCODING`. If you encounter an `EXT:ENCODING` `ERROR` in `clx/new-clx`, you can augment this variable to avoid it.

## 31.12. Customizing CLISP behavior

The user-customizable variables and functions are located in the package “CUSTOM” and thus can be listed using `(`APROPOS` "" "CUSTOM")`:

`CUSTOM:*ANSI*` | `CUSTOM:*APPLYHOOK*`
`CUSTOM:*APROPOS-DO-MORE*` | `CUSTOM:*APROPOS-MATCHER*`
`CUSTOM:*BREAK-ON-WARNINGS*` | `CUSTOM:*BROWSER*`
`CUSTOM:*BROWSERS*` | `CUSTOM:CLHS-ROOT`
`CUSTOM:*CLHS-ROOT-DEFAULT*` | `CUSTOM:*COERCE-FIXNUM-CHAR-ANSI*`
`CUSTOM:*COMPILE-WARNINGS*` | `CUSTOM:*COMPILED-FILE-TYPES*`
`CUSTOM:*CURRENT-LANGUAGE*` | `CUSTOM:*DEFAULT-FILE-ENCODING*`
`CUSTOM:*DEFAULT-FLOAT-FORMAT*` | `CUSTOM:*DEFAULT-TIME-ZONE*`
`CUSTOM:*DEFTYPE-DEPTH-LIMIT*` | `CUSTOM:*DEFUN-ACCEPT-SPECIALIZED-LAMBDA-LIST*`
`CUSTOM:*DEVICE-PREFIX*` | `CUSTOM:*EDITOR*`
`CUSTOM:*EQ-HASHFUNCTION*` | `CUSTOM:*EQL-HASHFUNCTION*`
`CUSTOM:*EQUAL-HASHFUNCTION*` | `CUSTOM:*ERROR-HANDLER*`
`CUSTOM:*EVALHOOK*` | `CUSTOM:*FILL-INDENT-SEXP*`
`CUSTOM:*FINI-HOOKS*` | `CUSTOM:*FLOATING-POINT-CONTAGION-ANSI*`
`CUSTOM:*FLOATING-POINT-RATIONAL-CONTAGION-ANSI*` | `CUSTOM:*FOREIGN-ENCODING*`
`CUSTOM:*HTTP-LOG-STREAM*` | `CUSTOM:*HTTP-PROXY*`
`CUSTOM:IMPNOTES-ROOT` | `CUSTOM:*IMPNOTES-ROOT-DEFAULT*`
`CUSTOM:*INIT-HOOKS*` | `CUSTOM:*INSPECT-BROWSER*`
`CUSTOM:*INSPECT-FRONTEND*` | `CUSTOM:*INSPECT-LENGTH*`
`CUSTOM:*INSPECT-PRINT-LENGTH*` | `CUSTOM:*INSPECT-PRINT-LEVEL*`
`CUSTOM:*INSPECT-PRINT-LINES*` | `CUSTOM:*LIB-DIRECTORY*`
`CUSTOM:*LOAD-COMPILING*` | `CUSTOM:*LOAD-ECHO*`
`CUSTOM:*LOAD-LOGICAL-PATHNAME-TRANSLATIONS-DATABASE*` | `CUSTOM:*LOAD-OBSOLETE-ACTION*`
`CUSTOM:*LOAD-PATHS*` | `CUSTOM:*LOOP-ANSI*`
`CUSTOM:*MERGE-PATHNAMES-ANSI*` | `CUSTOM:*MISC-ENCODING*`
`CUSTOM::*MODULE-PROVIDER-FUNCTIONS*` | `CUSTOM:*PACKAGE-TASKS-TREAT-SPECIALLY*`
`CUSTOM:*PARSE-NAMESTRING-ANSI*` | `CUSTOM:*PARSE-NAMESTRING-DOT-FILE*`
`CUSTOM:*PATHNAME-ENCODING*` | `CUSTOM:*PHASE-ANSI*`
`CUSTOM:*PPRINT-FIRST-NEWLINE*` | `CUSTOM:*PRINT-CLOSURE*`
`CUSTOM:*PRINT-EMPTY-ARRAYS-ANSI*` | `CUSTOM:*PRINT-INDENT-LISTS*`
`CUSTOM:*PRINT-SYMBOL-PACKAGE-PREFIX-SHORTEST*` | `CUSTOM:*PRINT-PATHNAMES-ANSI*`
`CUSTOM:*PRINT-PRETTY-FILL*` | `CUSTOM:*PRINT-RPARS*`
`CUSTOM:*PRINT-SPACE-CHAR-ANSI*` | `CUSTOM:*PRINT-UNREADABLE-ANSI*`
`CUSTOM:*PROMPT-BODY*` | `CUSTOM:*PROMPT-BREAK*`
`CUSTOM:*PROMPT-FINISH*` | `CUSTOM:*PROMPT-START*`
`CUSTOM:*PROMPT-STEP*` | `CUSTOM:*REOPEN-OPEN-FILE*`
`CUSTOM:*REPORT-ERROR-PRINT-BACKTRACE*` | `CUSTOM:*SAVEINITMEM-VERBOSE*`
`CUSTOM:*SEQUENCE-COUNT-ANSI*` | `CUSTOM:*SOURCE-FILE-TYPES*`
`CUSTOM:*SUPPRESS-CHECK-REDEFINITION*` | `CUSTOM:*SUPPRESS-SIMILAR-CONSTANT-REDEFINITION-WARNING*`
`CUSTOM:*SYSTEM-PACKAGE-LIST*` | `CUSTOM:*TERMINAL-ENCODING*`
`CUSTOM:*TRACE-INDENT*` | `CUSTOM:*USER-COMMANDS*`
`CUSTOM:*USER-LIB-DIRECTORY*` | `CUSTOM:*USER-MAIL-ADDRESS*`
`CUSTOM:*WARN-ON-FLOATING-POINT-CONTAGION*` | `CUSTOM:*WARN-ON-HASHTABLE-NEEDING-REHASH-AFTER-GC*`
`CUSTOM:*WITH-HTML-OUTPUT-DOCTYPE*` |

### Note

Some of these variables are platform-specific.

You should set these variables (and do whatever other customization you see fit) in the file `config.lisp` in the build directory before building CLISP. Alternatively, after building CLISP, or if you are using a binary distribution of CLISP, you can modify `config.lisp`, compile and load it, and then save the memory image. Finally, you can create an RC file which is loaded whenever CLISP is started.

## 31.13. Code Walker

You can use function `EXT:EXPAND-FORM` to expand all the macros, `SYMBOL-MACRO`s, etc, in a single form:

    (EXT:EXPAND-FORM '(macrolet ((bar (x) `(print ,x)))
                        (macrolet ((baz (x) `(bar ,x)))
                          (symbol-macrolet ((z 3))
                            (baz z)))))
    ⇒ (locally (print 3)) 	; the expansion
    ⇒ T 	; indicator: some expansion has actually been done

This is sometimes called a “code walker”, except that a code walker would probably leave the `MACROLET` and `SYMBOL-MACROLET` forms intact and just do the expansion.

### Warning

Function `EXT:EXPAND-FORM` is the exported part of the CLISP interpreter (AKA `EVAL`), so it expands forms by assuming the `EVAL-WHEN` situation `:EXECUTE` and is therefore unsuitable for forms that may later be passed to the compiler:

    (EXT:EXPAND-FORM '(EVAL-WHEN (:COMPILE-TOPLEVEL) (foo)))
    ⇒ NIL ;
    ⇒ T
    (EXT:EXPAND-FORM '(EVAL-WHEN (:LOAD-TOPLEVEL) (foo)))
    ⇒ NIL ;
    ⇒ T

## Chapter 32. Platform Specific Extensions

## 32.1. Random Screen Access

### Platform Dependent: UNIX, Win32 platforms only.

`(`SCREEN:MAKE-WINDOW`)`
  returns a WINDOW-STREAM. As long as this stream is open, the terminal is in cbreak/noecho mode. `*TERMINAL-IO*` should not be used for input or output during this time. (Use `EXT:WITH-KEYBOARD` and `EXT:*KEYBOARD-INPUT*` instead.)
`(`SCREEN:WITH-WINDOW` . `body`)`
  binds `SCREEN:*WINDOW*` to a WINDOW-STREAM and executes `body`. The stream is guaranteed to be closed when the body is left. During its execution, `*TERMINAL-IO*` should not be used, as above.
`(`SCREEN:WINDOW-SIZE` `window-stream`)`
  returns the window's size, as two values: height (= ymax+1) and width (= xmax+1).
`(`SCREEN:WINDOW-CURSOR-POSITION` `window-stream`)`
  returns the position of the cursor in the window, as two values: line (≥0, ≤ymax, 0 means top), column (≥0, ≤xmax, 0 means left margin).
`(`SCREEN:SET-WINDOW-CURSOR-POSITION` `window-stream` `line` `column`)`
  sets the position of the cursor in the window.
`(`SCREEN:CLEAR-WINDOW` `window-stream`)`
  clears the window's contents and puts the cursor in the upper left corner.
`(`SCREEN:CLEAR-WINDOW-TO-EOT` `window-stream`)`
  clears the window's contents from the cursor position to the end of window.
`(`SCREEN:CLEAR-WINDOW-TO-EOL` `window-stream`)`
  clears the window's contents from the cursor position to the end of line.
`(`SCREEN:DELETE-WINDOW-LINE` `window-stream`)`
  removes the cursor's line, moves the lines below it up by one line and clears the window's last line.
`(`SCREEN:INSERT-WINDOW-LINE` `window-stream`)`
  inserts a line at the cursor's line, moving the lines below it down by one line.
`(`SCREEN:HIGHLIGHT-ON` `window-stream`)`
  switches highlighted output on.
`(`SCREEN:HIGHLIGHT-OFF` `window-stream`)`
  switches highlighted output off.
`(`SCREEN:WINDOW-CURSOR-ON` `window-stream`)`
  makes the cursor visible, a cursor block in most implementations.
`(`SCREEN:WINDOW-CURSOR-OFF` `window-stream`)`
  makes the cursor invisible, in implementations where this is possible.

## 32.2. External Modules

### Platform Dependent: UNIX, Win32 platforms only.

List of Examples

32.1. Create a module set with GNU libc bindings

### Modules on Win32

Everything described in the section will work verbatim on Win32 when using Cygwin or MinGW, except for one thing - you will need to replace the `run` extension in `lisp.run` with the Win32 executable extension `exe`.

For historical reasons, all examples appear to assume UNIX and use the `run` file type (“extension”) for the CLISP runtime. This does not mean that they will not work on Win32.

### 32.2.1. Overview

External modules are a mechanism to add extensions (written in C, for example) to CLISP. Extending CLISP using an external module requires creating a module set and adding it to an existing linking set using clisp-link to prodice a new linking set which contains the extension.

#### Module Set

A module is a piece of code (C or Lisp) which defines extra (non-core) Lisp objects, symbols and functions. Together with link.sh, which describes how to add the module to an existing CLISP, it comprises a module set.

More formally, module set is a directory containing:

link.sh
  some /bin/sh commands, which prepare the directory for linking, and set some environment variables, see the section called “Module set variables”
all other files that define the module functionality
  needed by link.sh

In link.sh the module set directory is referred to as `$modulename/`.

A module name must consist of the characters `A`-`Z`, `a`-`z`, `_`, `0`-`9`.

The module name “clisp” is reserved.

#### Linking Set

A linking set is a collection of files (runtime, memory image &c) which allows performing two major tasks:

1. Running CLISP: to run a CLISP contained in some linking set `directory`, call

       $ directory/lisp.run -M directory/lispinit.mem

   or

       $ clisp -K directory

   (recommended, since it also passes `-B` to the runtime).

2. Adding a module set to create a new linking set which will contain the module functionality.

The CLISP build directory contains three linking sets in directories boot, base, and full, and a CLISP installation normally contains two linking sets: base, and full

More formally, a linking set is a directory containing at least these files:

`lisp.run`
  the executable runtime
`lispinit.mem`
  the memory image
`modules.h`
  the list of modules contained in this linking set
`modules.o`
  the compiled list of modules contained in this linking set
`makevars`

  some /bin/sh commands, setting the variables

  `CC` | the C compiler
  `CPPFLAGS` | flags for the C compiler, when preprocessing or compiling
  `CFLAGS` | flags for the C compiler, when compiling or linking
  `CLFLAGS` | flags for the C compiler, when linking
  `LIBS` | libraries to use when linking (either present in the linking set directory, or system-wide)
  `X_LIBS` | additional X Window System libraries to use
  `RANLIB` | the ranlib command
  `FILES` | the list of files needed when linking

all the `FILES`
  listed in `makevars`

#### Manipulating module sets and linking sets

Use clisp-link to create and install module sets and add them to linking sets.

See also Section 32.2.6, “Example”.

#### Module set variables

The following variables should be defined in link.sh.

`NEW_FILES`
  the space-separated list of object files that belong to the module set and will belong to every new linking set linked with this module set.
`NEW_LIBS`
  the space-separated list of object files, libraries or C compiler switches that need to be passed to the C compiler when linking the `lisp.run` belonging to a new linking set.
`NEW_MODULES`
  the space-separated list of the module names belonging to the module set. Normally, every `#P".c"` file in the module set defines a module of its own. The module name is usually derived from the file name.
`TO_LOAD`
  the space-separated list of Lisp files to load before building the `lispinit.mem` belonging to a new linking set.
`TO_PRELOAD` (optional)

  the space-separated list of Lisp files to load into an intermediate `lispinit.mem` file, before building the `lispinit.mem` belonging to a new linking set. This variable is usually used to create (or unlock) the Lisp `PACKAGE`s which must be present when the new `#P".c"` files are initialized. E.g., the `FFI:DEF-CALL-IN` functions must reside in already defined packages; see Example 32.7, “Calling Lisp from C”. You can find a live example in `modules/syscalls/preload.lisp` and `modules/syscalls/link.sh.in`.

  ### Warning

  If you are unlocking a package, you must also `DELETE` it from `CUSTOM:*SYSTEM-PACKAGE-LIST*` (see Section 31.2, “Saving an Image”) here and re-add it to `CUSTOM:*SYSTEM-PACKAGE-LIST*` in one of the `TO_LOAD` files. See, e.g., `modules/i18n/preload.lisp` and `modules/i18n/link.sh.in`.

### 32.2.2. Module initialization

Each module has two initialization functions:

void `module__`name`__init_function_1` (struct module_t* module)

  called only once when CLISP discovers while loading a memory image that there is a module present in the executable (`lisp.run`) which was not present at the time the image was saved. It can be used to create Lisp objects, e.g. functions or keywords, and is indeed used for that purpose by modprep.

  You do not have to define this function yourself; modprep and “FFI” will do that for you.

  If you use “FFI”, `(`FFI:C-LINES` :init-once ...)` will add code to this function.

  ### Warning

  The `PACKAGE`s must already exist and be unlocked, cf. `TO_PRELOAD`.

  ### Warning

  If you are using modprep and defining your own “init-once” function, it must call the `module__`name`__init_function_1__modprep` function!

void `module__`name`__init_function_2` (struct module_t* module)

  called every time CLISP starts. It can be used to bind names to foreign addresses, since the address will be different in each invocation of CLISP, and is indeed used for that purpose by “FFI” (e.g., by `FFI:DEF-CALL-OUT`). It can also be used to set parameters of the libraries to which the module interfaces, e.g., the `pcre` module sets `pcre_malloc` and `pcre_free`.

  You do not have to define this function yourself; modprep and “FFI” will do that for you.

  If you use “FFI”, `(`FFI:C-LINES` :init-always ...)` will add code to this function.

`name` is the module name.

See also Section 31.1, “Customizing CLISP Process Initialization and Termination”.

### 32.2.3. Module finalization

Each module has a finalization function

void `module__`name`__fini_function` (struct module_t* module)

  called before exiting CLISP.

  You do not have to define this function yourself; modprep and “FFI” will do that for you.

  If you use “FFI”, `(`FFI:C-LINES` :fini ...)` will add code to this function.

`name` is the module name.

See also Section 31.1, “Customizing CLISP Process Initialization and Termination”.

### 32.2.4. Function `EXT:MODULE-INFO`

Function `(`EXT:MODULE-INFO` `&OPTIONAL` `name` `verbose`)` allows one to inquire about what modules are available in the currently running image. When called without arguments, it returns the list of module names, starting with “clisp”. When `name` is supplied and names a module, 3 values are returned - `name`, `subr-count`, `object-count`. When `verbose` is non-`NIL`, the full list of module lisp function names written in C (Subrs) and the full list of internal lisp objects available in C code are additionally returned for the total of 5 values.

When `name` is `:FFI`, returns the list of shared libraries opened using `:LIBRARY`. When `verbose` is non-`NIL`, return the association list of DLL names and all foreign objects associated with it.

### 32.2.5. Dynamic module loading

#### Platform Dependent: Only in CLISP built without configure flag `--without-dynamic-modules`.

### Note

Dynamic loading does not work on all operating systems (`dlopen` or equivalent is required).

### Note

You will probably never need to call the function `SYS::DYNLOAD-MODULES` explicitly (this is why it is in “SYSTEM” and not in “EXT”). You should install your module with

    $ clisp-link install name

and load it with `(`REQUIRE` `name`).`

Function `(`SYS::DYNLOAD-MODULES` `filename` ({`name`}+))` loads a shared object file or library containing a number of named external CLISP modules.

### Note

This facility cannot be used to access arbitrary shared libraries. To do that, use the `:LIBRARY` argument to `FFI:DEF-CALL-OUT` and `FFI:DEF-C-VAR` instead.

External modules for CLISP are shared objects (dynamic libraries) that contain the `module__`name`__subr_tab` variable, among others. This serves to register external functions which operate on Lisp-level structures with CLISP.

To use `dlopen` with modules, you should add `-fPIC` to the module's compilation options. Something like

    $ cc -shared -o name.so name.o

may be needed to produce the shared object file.

### 32.2.6. Example

List of Examples

32.1. Create a module set with GNU libc bindings

Example 32.1. Create a module set with GNU libc bindings

To link in the “FFI” bindings for the GNU/Linux operating system, the following steps are needed. (Step 1 and step 2 need not be executed in this order.)

1. Create a new module set

       $ clisp-link create linux /pathname/bindings/linux.c

2. Modify the newly created `linux/link.sh`

   1. add `-lm` to the libraries

      replace

          NEW_LIBS="$file_list"

      with

          NEW_LIBS="$file_list -lm"

   2. load `linux.fas` before saving the memory image

      replace

          TO_LOAD=''

      with

          TO_LOAD='/pathname/bindings/linux.fas'

3. Compile `linux.lisp`, creating `linux.c`

       $ clisp -c /pathname/bindings/linux.lisp

4. Create a new linking set

       $ clisp-link add base base+linux linux

5. Run and try it

       $ base+linux/lisp.run -M base+linux/lispinit.mem -x '(linux:stat "/tmp")'

### 32.2.7. Module tools

There are some tools to facilitate easy module writing.

#### 32.2.7.1. Modprep

If your module is written in C, you can pre-process your sources with modprep in the CLISP distribution and define lisp functions with the `DEFUN` macro:

    DEFUN(MY-PACKAGE:MY-FUNCTION-NAME, arg1 arg2 &KEY FOO BAR) {
      if (!boundp(STACK_0)) STACK_0 = fixnum(0); /* BAR */
      if (!boundp(STACK_1)) STACK_1 = fixnum(1); /* FOO */
      pushSTACK(`MY-PACKAGE::SOME-SYMBOL`); /* create a symbol in the package */
      pushSTACK(`#(:THIS :IS :A :VECTOR)`); /* some vector, created once */
      pushSTACK(``MY-PACKAGE::MY-FUNCTION-NAME``); /* double `` means FUNCTION */
      VALUES1(listof(7)); /* cons up a new list and clean up the STACK */
    }

Then `(MY-PACKAGE:MY-FUNCTION-NAME 'A 12 :FOO T)` will return (A 12 T 0 MY-PACKAGE::SOME-SYMBOL #(:THIS :IS :A :VECTOR) #<ADD-ON-SYSTEM-FUNCTION MY-PACKAGE:MY-FUNCTION-NAME>) (assuming you `EXPORT`ed `MY-FUNCTION-NAME` from “MY-PACKAGE”).

Note that the arguments are passed on the `STACK` (last argument being the top) which has to be cleaned up before exit.

Another useful macros are:

`DEFVAR`
  create a GC-visible private object
`DEFFLAGSET`
  define a C function which will remove several flag arguments from the `STACK` and return the combined flag value
`DEFCHECKER`
  define a map from cpp constants to lisp symbols and functions that map between them, checking that the argument is appropriate

See `modules/syscalls/calls.c` and other included modules for more examples and file modprep for full documentation.

### Warning

If you manipulate Lisp objects, you need to watch out for GC-safety.

#### 32.2.7.2. clisp.h

If your module is written in C, you will probably want to `#include "clisp.h"` to access CLISP objects. You will certainly need to read `"clisp.h"` and some code in included modules, but here are some important hints that you will need to keep in mind:

- Lisp objects have type object.
- Variables of this type are invalidated by lisp memory allocation (`allocate_*()` functions) - but not C allocations (`malloc` et al) - and must be saved on the `STACK` using cpp macros `pushSTACK()`, `popSTACK()` and `skipSTACK()`.
- Access object slots using the appropriate `TheFoo()` macro, e.g., `TheCons(my_cons)->Car`, but first check the type with `consp()`.
- Arguments are passed on the `STACK`, as illustrated in the above example.

- Wrap your system calls in `begin_system_call()`/`end_system_call()` pairs. These macros, defined in `"clisp.h"`, save and restore registers used by CLISP which could be clobbered by a system call.

  If the system call could block (e.g., `read`) you need to use `begin_blocking_system_call()` and `end_blocking_system_call()` instead. This will allow other threads to run while yours is inside the system call. This means that garbage-collection could happen while you are inside this system call and, thus, that all objects of type object are invalidated by the call. See also Section 35.5, “The burden of garbage-collection upon the rest of CLISP” and Section 35.8, “Garbage Collection and Multithreading”.

#### 32.2.7.3. Exporting

If your module uses “FFI” to interface to a C library, you might want to make your module package `:CASE-SENSITIVE` and use `exporting.lisp` in the CLISP distribution to make “FFI” forms and `DEFUN`, `DEFMACRO` at al export the symbols they define. See `modules/netica/`, `modules/matlab/` and `modules/bindings/` for examples.

### 32.2.8. Trade-offs: “FFI” vs. C modules

When deciding how to write a module: whether to use “FFI” or to stick with C and modprep, one has to take into account several issues:

Speed: C wins

  “FFI” has a noticeable overhead: compare `RAWSOCK:HTONS` (defined in `modules/rawsock/rawsock.c`) with

      (FFI:DEF-CALL-OUT htons (:NAME "htons") (:LIBRARY :default)
        (:ARGUMENTS (s ffi:short)) (:RETURN-TYPE ffi:short) (:LANGUAGE :stdc))

  and observe that `RAWSOCK:HTONS` is almost 3 times as fast (this really does compare the “FFI” overhead to the normal lisp function call because `htons` is computationally trivial). This difference will matter only if you call a simple function very many times, in which case it would make sense to put the loop itself into C.

Portability: C wins
  1. “FFI” is not as widely ported as CLISP, so it is possible that you will face a platform where CLISP runs but “FFI” is not present.
  2. It is much easier to handle portability in C: observe the alternative implementations of `htonl` et al in `modules/rawsock/rawsock.c`.
  3. Certain C structures have different layout on different platforms, and functions may take 64-bit arguments on some platforms and 32-bit arguments on others; so the “FFI” code has to track those differences, while C will mostly take care of these things for you.
Code size: “FFI” wins
  You need to type much fewer characters with “FFI”, and, if you use the `:LIBRARY` argument to `FFI:DEF-CALL-OUT` and `FFI:DEF-C-VAR`, you do not need to leave your CLISP session to try out your code. This is a huge advantage for rapid prototyping.
UI: C wins
  To produce a nice lispy UI (using `&OPTIONAL` and `&KEY`word arguments etc), you will need to write wrappers to your `FFI:FOREIGN-FUNCTION`s, while in C you can do that directly. The same goes for “polymorphism”: accepting different argument types (like, e.g., `POSIX:RESOLVE-HOST-IPADDR` does) would require a lisp wrapper for `FFI:FOREIGN-FUNCTION`s.
Learning curve: unclear

  If you are comfortable with C, you might find the CLISP C module facilities (e.g., modprep) very easy to use.

  CLISP “FFI”, on the other hand, is quite high-level, so, if you are more comfortable with high-level languages, you might find it easier to write “FFI” forms than C code.

Safety: unclear
  One can get a segfault either way: if your `FFI:DEF-CALL-OUT` form does not describe the C function's expectations with respect to the arguments and return values (including `ALLOCATION`), you will probably learn that the hard way. If the module is written in C, all the opportunities to shoot oneself in the foot (and other body parts) are wide open (although well known to most C users). However, with C, one has to watch for GC-safety too.
System requirements: “FFI” wins

  Some Linux distributions offer separate library (containing shared libraries only) and development (containing static libraries and C headers) packages.

  - When developing using “FFI” with `:LIBRARY` (and avoiding `FFI:DEF-C-CONST`), the development package is not needed.
  - When developing with modprep, the development package is necessary.
  - When distributing module (built with either “FFI” or modprep), only the library package is needed.

### Note

The granularity of the choice is per function: the same module can use both modprep and “FFI”.

### Note

It is not a good idea to have both `foo.lisp` and `foo.c` files in a module, because if you ever add an “FFI” form to the former, `COMPILE-FILE` will overwrite the latter.

### 32.2.9. Modules included in the source distribution

A few modules come with the source distribution of CLISP (but are not necessarily built in a particular binary distribution).

To use modules, read `unix/INSTALL` and build CLISP in a directory `build-dir` with, e.g.,

    $ ./configure --with-module=pcre --with-module=clx/new-clx --cbc build-dir

then run it with

    $ ./build-dir/clisp -K full

This will create a base linking set with modules `i18n`, `regexp` and `syscalls` (and maybe `readline`); and a full linking set with modules `clx/new-clx` and `pcre` in addition to the 3 (or 4) base modules.

Here we list the included modules by their general theme. See Chapter 33, Extensions Implemented as Modules for individual module documentation.

#### 32.2.9.1. Base Modules

The default build process includes the following modules in both base and full linking sets:

`i18n`
  Internationalization of User Programs.
`regexp`
  The POSIX Regular Expressions matching, compiling, executing.
`syscalls`
  Use some system calls in a platform-independent way.
`readline` (only when both GNU readline and “FFI” are available)
  Some advanced readline and history features are exported using this module.

The composition of the full linking set depends on the platform and on the vendor preferences.

#### 32.2.9.2. Database, Directory et al

`gdbm`
  Interface to GNU DataBase Manager by Masayuki Onjo.
`berkeley-db`
  Berkeley DB interface.
`dirkey`
  Directory Access (LDAP, Win32 registry etc).
`postgresql`
  Access PostgreSQL from CLISP.
`oracle`
  Access Oracle RDBMS from CLISP; by John Hinsdale.

#### 32.2.9.3. Mathematics, Data Mining et al

`libsvm`
  Build Support Vector Machine models using LibSVM inside CLISP.
`pari`
  Interface to the computer algebra system PARI.
`matlab`
  Do matrix computations via MATLAB.
`netica`
  Work with Bayesian belief networks and influence diagrams using Netica C API.

#### 32.2.9.4. Matching, File Processing et al

`pcre`
  The Perl Compatible Regular Expressions matching, compiling, executing.
`zlib`
  Compress `VECTOR`s using ZLIB.

#### 32.2.9.5. Communication, Networking

`rawsock`
  Raw socket access.
`dbus`
  Interface to D-Bus.
`fastcgi`
  Access FastCGI from CLISP; by John Hinsdale.

#### 32.2.9.6. Graphics

CLX

  Call Xlib functions from CLISP. Two implementations are supplied:

  `clx/mit-clx`, from MIT https://www.x.org/archive/unsupported/lib/CLX/
    the standard implementation
  `clx/new-clx`, by Gilbert Baumann

    faster, with additional features, but not quite complete yet. Please try it first and use `clx/mit-clx` only if `clx/new-clx` does not work for you. `clx/new-clx` comes with several demos, please try them using

        $ clisp -K full -i modules/clx/new-clx/demos/clx-demos.lisp -x '(clx-demos:run-all-demos)'

    and follow the intructions.

  This functionality is documented in the manual https://common-lisp.net/project/cmucl/doc/clx/, also available in the CLISP source distribution as `modules/clx/clx-manual.tar.gz`.

`gtk2`
  Use GTK+ and Glade to create GUI by James Bailey.

#### 32.2.9.7. Bindings

Call the operating system functions from CLISP. The following platforms are supported:

`bindings/glibc`
  Linux/GNU libc
`bindings/win32`
  Win32

#### 32.2.9.8. Toys and Games

`queens`
  Compute the number of solutions to the `n`-queens problem on a `n`×`n` chessboard (a toy example for the users to explore the CLISP module system).
`modules/clx/new-clx/demos/sokoban.lisp`
  a demo which comes with `clx/new-clx`.

#### 32.2.9.9. Miscellaneous

`asdf`
  A system definition facility.

## 32.3. The Foreign Function Call Facility

### Platform Dependent: Many UNIX, Win32 platforms only.

List of Examples

32.2. Simple declarations and access
32.3. External C variable and some accesses
32.4. Calling an external function
32.5. Another example for calling an external function
32.6. Accessing cpp macros
32.7. Calling Lisp from C
32.8. Calling Lisp from C dynamically
32.9. Variable size arguments: calling `gethostname` from CLISP
32.10. Accessing variables in shared libraries
32.11. Controlling validity of resources
32.12. Floating point arrays

### 32.3.1. Introduction

This facility, also known as “Foreign Language Interface”, allows one to call a function implemented in C from inside CLISP and to do many related things, like inspect and modify foreign memory, define a “callback” (i.e., make a lisp function available to the C world), etc. To use this facility, one writes a foreign function description into an ordinary Lisp file, which is then compiled and loaded as usual; or just evaluates the appropriate form in the read-eval-print loop.

There are two basic ways to do define a foreign function:

1. Use `dlopen` and `dlsym` to get to the location of the function code in a dynamic library. To access this facility, pass the `:LIBRARY` option to `FFI:DEF-CALL-OUT` and `FFI:DEF-C-VAR`.

   Unfortunately, this functionality is not available on some operating systems, and, also, it offers only a part of the foreign functionality: cpp macros and `inline` functions cannot be accessed this way. On the other hand, this functionality is available in the read-eval-print loop and does not require a C compiler.

2. Use a somewhat less direct way: when you do not use the `:LIBRARY` argument, `COMPILE-FILE` produces a `#P".c"` file (in addition to a `#P".fas"` and a `#P".lib"`). Then you compile (with a C compiler) and link it into CLISP (statically, linking it into `lisp.a`, or dynamically, loading it into a running CLISP using `dlopen` and `dlsym`). This way you can use any functionality your foreign library exports, whether using ordinary functions, `inline` functions, or cpp macros (see Example 32.6, “Accessing cpp macros”).

All symbols relating to the foreign function interface are exported from the package “FFI”. To use them, `(`USE-PACKAGE` “FFI”)`.

Special “FFI” forms may appear anywhere in the Lisp file.

### 32.3.2. Overview

These are the special “FFI” forms. We have taken a pragmatic approach: the only foreign languages we support for now are C and ANSI C.

### Note

Unless specifically noted otherwise, type specification parameters are not evaluated, so that they can be compiled by `FFI:PARSE-C-TYPE` into the internal format at macroexpansion time.

High-level “FFI” forms; `name` is any Lisp `SYMBOL`; `c-name` is a `STRING`

`(`FFI:DEF-C-TYPE` `name` `&OPTIONAL` `c-type`)`

  This form makes `name` a shortcut for `c-type`. Note that `c-type` may already refer to `name`. Forward declarations of types are not possible, however.

  When `c-type` is omitted, the type is assumed to be an integer, and its size and signedness are determined at link time, e.g., `(`FFI:DEF-C-TYPE` size_t)`.

`(`FFI:DEF-C-VAR` `name` {`option`}*)`

  This form defines a `FFI:FOREIGN-VARIABLE`. `name` is the Lisp name, a regular Lisp `SYMBOL`.

  Options for `FFI:DEF-C-VAR`

  `(`:NAME` `c-name`)`
    specifies the name as seen from C, as a `STRING`. If not specified, it is derived from the print name of the Lisp name.
  `(`:TYPE` `c-type`)`
    specifies the variable's foreign type.
  `(`:READ-ONLY` `BOOLEAN`)`
    If this option is specified and non-`NIL`, it will be impossible to change the variable's value from within Lisp (using `SETQ` or similar).
  `(:ALLOC `ALLOCATION`)`
    This option can be either `:NONE` or `:MALLOC-FREE` and defaults to `:NONE`. If it is `:MALLOC-FREE`, any values of type FFI:C-STRING, FFI:C-PTR, FFI:C-PTR-NULL, FFI:C-ARRAY-PTR within the foreign value are assumed to be pointers to `malloc`-allocated storage, and when `SETQ` replaces an old value by a new one, the old storage is freed using `free` and the new storage allocated using `malloc`. If it is `:NONE`, `SETQ` assumes that the pointers point to good storage (not `NULL`!) and overwrites the old values by the new ones. This is dangerous (just think of overwriting a string with a longer one or storing some data in a `NULL` pointer...) and deprecated.
  `(`:LIBRARY` `name`)`
    Specifies the (optional) dynamic library which contains the variable, the default is set by `FFI:DEFAULT-FOREIGN-LIBRARY`.
  `(`:VERSION` `version`)`
    Specifies the (optional) symbol version in the library (therefore, if `:VERSION` is supplied, `:LIBRARY` must also be supplied)
  `(`:DOCUMENTATION` `string`)`
    Specifies the (optional) `VARIABLE` documentation.
`(`FFI:DEF-C-CONST` `name` {`option`}*)`

  This form defines a Lisp constant variable `name` whose value is determined at build time using an internal `FFI:FOREIGN-FUNCTION`.

  Options for `FFI:DEF-C-CONST`

  `(`:NAME` `c-name`)`
    specifies the name as seen from C, as a `STRING`. If not specified, it is derived from the print name of the Lisp name.
  `(`:TYPE` `c-type`)`

    specifies the constant's foreign type, one of

    FFI:INT
    FFI:C-STRING
    FFI:C-POINTER

  `(`:GUARD` `string`)`

    specifies the cpp check to wrap around `c-name`, defaults to `"defined(`c-name`)"`; can be `NIL` to omit the test. When the test fails, `name` is unbound.

  `(`:DOCUMENTATION` `string`)`
    Specifies the (optional) `VARIABLE` documentation.

  See also Example 32.6, “Accessing cpp macros”.

`(`FFI:DEF-CALL-OUT` `name` {`option`}*)`

  This form defines a named call-out function (a foreign function called from Lisp: control flow temporarily leaves Lisp).

  Options for `FFI:DEF-CALL-OUT`

  `(`:NAME` `c-name`)`
    Any Lisp function call to `#'`name`` is redirected to call the C function `c-name`.
  `(`:ARGUMENTS` {(`argument` `c-type` [`PARAM-MODE` [`ALLOCATION`]])}*)`
  `(`:RETURN-TYPE` `c-type` [`ALLOCATION`])`
    Argument list and return value, see Section 32.3.8, “Argument and result passing conventions” and Section 32.3.9, “Parameter Mode”.
  `(`:LANGUAGE` `language`)`
    See Section 32.3.4, “The choice of the C flavor”.
  `(:BUILT-IN `BOOLEAN`)`
    When the function is a C built-in, the full prototype will be output (unless suppressed by `FFI:*OUTPUT-C-FUNCTIONS*`).
  `(`:LIBRARY` `name`)`
    Specifies the (optional) dynamic library which contains the function, the default is set by `FFI:DEFAULT-FOREIGN-LIBRARY`.
  `(`:VERSION` `version`)`
    Specifies the (optional) symbol version in the library (therefore, if `:VERSION` is supplied, `:LIBRARY` must also be supplied).
  `(:GUARD `guard`)`

    Specifies how to wrap the C code in the cpp conditionals for portability and defaults to `FFI:*FOREIGN-GUARD*`:

    `NIL`
      Do nothing
    `T`
      Rely on GNU autoconf feature detection as described in `FFI:*FOREIGN-GUARD*`.
    anything else

      Use as is, e.g., in `modules/bindings/glibc/linux.lisp`:

          (def-call-out canonicalize_file_name (:arguments (name c-string))
            (:return-type c-string :malloc-free) (:guard "defined(__USE_GNU)"))

  `(`:DOCUMENTATION` `string`)`
    Specifies the (optional) `FUNCTION` documentation.

  See also Section 32.3.7, “Foreign functions”.

`(`FFI:DEF-CALL-IN` `function` {`option`}*)`

  This form defines a callback - a named call-in function (i.e., a Lisp function called from the foreign language: control flow temporary enters Lisp)

  Options for `FFI:DEF-CALL-IN`

  `(`:NAME` `c-name`)`
    Any C function call to the C function `c-name` is redirected to call the Common Lisp function `function`, which should be a function name.
  `(`:ARGUMENTS` {(`argument` `c-type` [`PARAM-MODE` [`ALLOCATION`]])}*)`
  `(`:RETURN-TYPE` `c-type` [`ALLOCATION`])`
    Argument list and return value, see Section 32.3.8, “Argument and result passing conventions” and Section 32.3.9, “Parameter Mode”.
  `(`:LANGUAGE` `language`)`
    See Section 32.3.4, “The choice of the C flavor”.

  See also Section 32.3.7, “Foreign functions”.

`(`FFI:OPEN-FOREIGN-LIBRARY` `name` `&KEY` :REQUIRE)`

  Open (load) a shared foreign library.

  Some shared libraries depend on other shared libraries and this dependency can be specified using the `:REQUIRE` argument.

  Unless the library has dependencies, this is only needed if you want to test for presence of a library without creating a foreign object referencing its contents. When you create a `FFI:FOREIGN-VARIABLE` or a `FFI:FOREIGN-FUNCTION` using `FFI:DEF-C-VAR` or `FFI:DEF-CALL-OUT` with a `:LIBRARY` argument, the library `name` is opened automatically.

  E.g., `libgsl.so` requires `libgslcblas.so`:

      (FFI:OPEN-FOREIGN-LIBRARY "libgsl.so")
      *** - FFI:OPEN-FOREIGN-LIBRARY: Cannot open library "libgsl.so": "/usr/lib64/libgsl.so: undefined symbol: cblas_ctrmv"

  so a common way is to pre-open the dependency:

      (FFI:OPEN-FOREIGN-LIBRARY "libgslcblas.so")
      (FFI:DEF-CALL-OUT gsl_cheb_alloc (:LIBRARY "libgsl.so") (:language :stdc)
        (:arguments (n ffi:int)) (:return-type ffi:c-pointer))
      ⇒ GSL_CHEB_ALLOC

  Alas, this would work in the current image only: if you save the image, `GSL_CHEB_ALLOC` will not work there because CLISP will try to re-open `libgsl.so` and fail as above. However, using the `:REQUIRE` argument will tell CLISP to re-open both libraries in the right order:

      $ clisp
      > (FFI:OPEN-FOREIGN-LIBRARY "libgsl.so" :require '("libgslcblas.so"))
      > (FFI:DEF-CALL-OUT gsl_cheb_alloc (:library "libgsl.so") (:language :stdc)
        (:arguments (n ffi:int)) (:return-type ffi:c-pointer))
      > (EXT:SAVEINITMEM "foo" :executable t)
      > (EXT:EXIT)
      $ ./foo
      > (gsl_cheb_alloc 10)
      #<FFI:FOREIGN-ADDRESS #x0000000017AC38A0>

`(`FFI:CLOSE-FOREIGN-LIBRARY` `name`)`

  Close (unload) a shared foreign library (opened by `FFI:OPEN-FOREIGN-LIBRARY` or the `:LIBRARY` argument to `FFI:DEF-CALL-OUT` or `FFI:DEF-C-VAR`).

  If you want to modify your shared library, you need to close it using `FFI:CLOSE-FOREIGN-LIBRARY` first. When you use a `FFI:FOREIGN-VARIABLE` or a `FFI:FOREIGN-FUNCTION` which resides in the library `name`, it will be re-opened automatically.

`(`FFI:DEFAULT-FOREIGN-LIBRARY` `library-name`)`

  This macro sets the default `:LIBRARY` argument for `FFI:DEF-CALL-OUT` and `FFI:DEF-C-VAR`. `library-name` should be `NIL` (meaning use the C file produced by `COMPILE-FILE`), a `STRING`, or, depending on the underlying `dlsym` or `dlvsym` implementation, `:DEFAULT` or `:NEXT`.

  The default is set separately in each compilation unit, so, if you are interfacing to a single library, you can set this variable in the beginning of your lisp file and omit the `:LIBRARY` argument throughout the file.

`(`FFI:DEF-C-STRUCT` `name` (`symbol` `c-type`)*)`

  This form defines `name` to be both a `STRUCTURE-CLASS` and a foreign C type with the given slots. If this class representation overhead is not needed one should consider writing `(`FFI:DEF-C-TYPE` `name` (FFI:C-STRUCT {`LIST` | `VECTOR`} (`symbol` `c-type`)*))` instead. `name` is a `SYMBOL` (structure name) or a `LIST` whose `FIRST` element is the structure name and the `REST` is options. Two options are supported at this time:

  Options for `FFI:DEF-C-STRUCT`

  `:TYPEDEF`
    means that the name of this structure is a C type defined with `typedef` elsewhere.
  `:EXTERNAL`
    means that this structure is defined in a C header file that you include with, e.g., `(`FFI:C-LINES` "#include <filename.h>~%")`.

  These options determine how the struct is written to the `#P".c"`.

`(`FFI:DEF-C-ENUM` `name` {`symbol` | (`symbol` [`value`])}*)`

  This form defines `symbol`s as constants, similarly to the C declaration enum { `symbol` [= `value`], ... };

  You can use `(`FFI:ENUM-FROM-VALUE` `name` `value`)` and `(`FFI:ENUM-TO-VALUE` `name` `symbol`)` to convert between the numeric and symbolic representations (of course, the latter function boils down to `SYMBOL-VALUE` plus a check that the `symbol` is indeed a constant defined in the `FFI:DEF-C-ENUM` `name`).

`(`FFI:C-LINES` `format-string` {`argument`}*)`

  This form outputs the string `(`FORMAT` `NIL` `format-string` {`argument`}*)` to the C output file's top level. This is usually used to include the relevant header files, see `:EXTERNAL` and `FFI:*OUTPUT-C-FUNCTIONS*`.

  When `format-string` is not a `STRING`, is should be a `SYMBOL`, and then the `STRING` `(`FORMAT` `NIL` {`argument`}*)` is added to the appropriate C function:

  `:INIT-ALWAYS`
  `:INIT-ONCE`
    initialization function
  `:FINI`
    finalization function
`(`FFI:ELEMENT` `c-place` `index1` ... `indexn`)`
  Array element: If `c-place` is of foreign type `(FFI:C-ARRAY `c-type` (`dim1` ... `dimn`))` and 0 ≤ `index1` < `dim1`, ..., 0 ≤ `indexn` < `dimn`, this will be the place corresponding to `(`AREF` `c-place` `index1` ... `indexn`)` or ``c-place`[`index1`]...[`indexn`]`. It is a place of type `c-type`. If `c-place` is of foreign type `(FFI:C-ARRAY-MAX `c-type` `dim`)` and 0 ≤ `index` < `dim`, this will be the place corresponding to `(`AREF` `c-place` `index`)` or ``c-place`[`index`]`. It is a place of type `c-type`.
`(`FFI:DEREF` `c-place`)`
  Dereference pointer: If `c-place` is of foreign type `(FFI:C-PTR `c-type`)`, `(FFI:C-PTR-NULL `c-type`)` or `(FFI:C-POINTER `c-type`)`, this will be the place the pointer points to. It is a place of type `c-type`. For `(FFI:C-PTR-NULL `c-type`)`, the `c-place` may not be `NULL`.
`(`FFI:SLOT` `c-place` `slot-name`)`
  Struct or union component: If `c-place` is of foreign type `(FFI:C-STRUCT `class` ... (`slot-name` `c-type`) ...)` or of type `(FFI:C-UNION ... (`slot-name` `c-type`) ...)`, this will be of type `c-type`.
`(`FFI:CAST` `c-place` `c-type`)`
  Type change: A place denoting the same memory locations as the original `c-place`, but of type `c-type`.
`(`FFI:OFFSET` `c-place` `offset` `c-type`)`
  Type change and displacement: return a place denoting a memory locations displaced from the original `c-place` by an `offset` counted in bytes, with type `c-type`. This can be used to resize an array, e.g. of `c-type` `(FFI:C-ARRAY uint16 `n`)` via `(`FFI:OFFSET` `c-place` 0 '(FFI:C-ARRAY uint16 `k`))`.
`(`FFI:C-VAR-ADDRESS` `c-place`)`
  Return the address of `c-place` as a Lisp object of type `FFI:FOREIGN-ADDRESS`. This is useful as an argument to foreign functions expecting a parameter of C type FFI:C-POINTER.
`(`FFI:C-VAR-OBJECT` `c-place`)`
  Return the `FFI:FOREIGN-VARIABLE` object underlying the `c-place`. This is also an acceptable argument type to a FFI:C-POINTER declaration.
`(`FFI:TYPEOF` `c-place`)`
  returns the `c-type` corresponding to the `c-place`.
`(`FFI:SIZEOF` `c-type`)`
`(`FFI:SIZEOF` `c-place`)`

  The first form returns the size and alignment of the C type `c-type`, measured in bytes.

  The second form returns the size and alignment of the C type of `c-place`, measured in bytes.

`(`FFI:BITSIZEOF` `c-type`)`
`(`FFI:BITSIZEOF` `c-place`)`

  The first form returns the size and alignment of the C type `c-type`, measured in bits.

  The second form returns the size and alignment of the C type of `c-place`, measured in bits.

`(`FFI:FOREIGN-ADDRESS-UNSIGNED` `foreign-entity`)`
`(`FFI:UNSIGNED-FOREIGN-ADDRESS` `number`)`

  `FFI:FOREIGN-ADDRESS-UNSIGNED` returns the `INTEGER` address embodied in the Lisp object of type `FFI:FOREIGN-ADDRESS`, `FFI:FOREIGN-POINTER`, `FFI:FOREIGN-VARIABLE` or `FFI:FOREIGN-FUNCTION`.

  `FFI:UNSIGNED-FOREIGN-ADDRESS` returns a `FFI:FOREIGN-ADDRESS` object pointing to the given `INTEGER` address.

`(`FFI:FOREIGN-ADDRESS` `foreign-entity`)`

  `FFI:FOREIGN-ADDRESS` is both a type name and a selector/constructor function. It is the Lisp object type corresponding to a FFI:C-POINTER external type declaration, e.g. a call-out function with `(`:RETURN-TYPE` FFI:C-POINTER)` yields a Lisp object of type `FFI:FOREIGN-ADDRESS`.

  The function extracts the object of type `FFI:FOREIGN-ADDRESS` living within any `FFI:FOREIGN-VARIABLE` or `FFI:FOREIGN-FUNCTION` object. If the `foreign-entity` already is a `FFI:FOREIGN-ADDRESS`, it returns it. If it is a `FFI:FOREIGN-POINTER` (e.g. a base foreign library address), it encapsulates it into a `FFI:FOREIGN-ADDRESS` object, as suitable for use with a FFI:C-POINTER external type declaration. It does not construct addresses out of `NUMBER`s, `FFI:UNSIGNED-FOREIGN-ADDRESS` must be used for that purpose.

`(`FFI:FOREIGN-VARIABLE` `foreign-entity` `c-type-internal` `&KEY` `name`)`
  This constructor creates a new `FFI:FOREIGN-VARIABLE` from the given `FFI:FOREIGN-ADDRESS` or `FFI:FOREIGN-VARIABLE` and the internal C type descriptor (as obtained from `FFI:PARSE-C-TYPE`). `name`, a `STRING`, is mostly useful for documentation and interactive debugging since it appears in the printed representation of the `FFI:FOREIGN-VARIABLE` object, as in `#<`FFI:FOREIGN-VARIABLE` "foo" #x0ADD4E55>`. In effect, this is similar to `FFI:CAST` (or rather `(`FFI:OFFSET` ... 0 ...)` for places), except that it works with `FFI:FOREIGN-ADDRESS` objects and allows caching of the internal C types.
`(`FFI:FOREIGN-FUNCTION` `foreign-entity` `c-type-internal` `&KEY` `name`)`

  This constructor creates a `FFI:FOREIGN-FUNCTION` from the given `FFI:FOREIGN-ADDRESS` or `FFI:FOREIGN-FUNCTION` and the internal C type descriptor (as obtained from `(`FFI:PARSE-C-TYPE` '(FFI:C-FUNCTION ...))`, in which case it is important to specify the `:LANGUAGE` because the expressions are likely to be evaluated at run time, outside the compilation unit). The `name`, a `STRING`, is mostly useful for documentation and interactive debugging since it appears in the printed representation of the `FFI:FOREIGN-FUNCTION` object, e.g., `#<`FFI:FOREIGN-FUNCTION` "foo" #x0052B060>`. It is inherited from the given `FFI:FOREIGN-FUNCTION` object when available.

  See also Section 32.3.7, “Foreign functions”.

`(`FFI:VALIDP` `foreign-entity`)`
`(`SETF` (`FFI:VALIDP` `foreign-entity`) `value`)`

  This predicate returns `NIL` if the `foreign-entity` (e.g. the Lisp equivalent of a FFI:C-POINTER) refers to a pointer which is invalid (e.g., because it comes from a previous Lisp session). It returns `T` if `foreign-entity` can be used within the current Lisp process (thus it returns `T` for all non-foreign arguments).

  You can invalidate a foreign object using `(`SETF` `FFI:VALIDP`)`. You cannot resurrect a zombie, nor can you kill a non-foreign object.

`(`FFI:FOREIGN-POINTER` `foreign-entity`)`
  `FFI:FOREIGN-POINTER` returns the `FFI:FOREIGN-POINTER` associated with the Lisp object of type `FFI:FOREIGN-ADDRESS`, `FFI:FOREIGN-POINTER`, `FFI:FOREIGN-VARIABLE` or `FFI:FOREIGN-FUNCTION`.
`(`FFI:SET-FOREIGN-POINTER` `foreign-entity` {`foreign-entity` | `:COPY`})`
  `FFI:SET-FOREIGN-POINTER` changes the `FFI:FOREIGN-POINTER` associated with the Lisp object of type `FFI:FOREIGN-ADDRESS`, `FFI:FOREIGN-VARIABLE` or `FFI:FOREIGN-FUNCTION` to that of the other entity. With `:COPY`, a fresh `FFI:FOREIGN-POINTER` is allocated. The original `foreign-entity` still points to the same object and is returned. This is particularly useful with `(`SETF` `FFI:VALIDP`)`, see Example 32.11, “Controlling validity of resources”.
`(`FFI:WITH-FOREIGN-OBJECT` (`variable` `c-type` [`initarg`]) `body`)`
`(`FFI:WITH-C-VAR` (`variable` `c-type` [`initarg`]) `body`)`

  These forms allocate space on the C execution stack, bind respectively a `FFI:FOREIGN-VARIABLE` object or a local `SYMBOL-MACRO` to `variable` and execute `body`.

  When `initarg` is not supplied, they allocate space only for `(`FFI:SIZEOF` `c-type`)` bytes. This space is filled with zeroes. E.g., using a `c-type` of FFI:C-STRING or even `(FFI:C-PTR (FFI:C-ARRAY uint8 32))` (!) both allocate space for a single pointer, initialized to `NULL`.

  When `initarg` is supplied, they allocate space for an arbitrarily complex set of structures rooted in `c-type`. Therefore, FFI:C-ARRAY-MAX, `#()` and `""` are your friends for creating a pointer to the empty arrays:

      (with-c-var (v '(c-ptr (c-array-max uint8 32)) #())
        (setf (element (deref v) 0) 127) v)

  `c-type` is evaluated, making creation of variable sized buffers easy:

      (with-c-var (fv `(c-array uint8 ,(length my-vector)) my-vector)
        (print fv))

`(`FFI:FOREIGN-VALUE` `FFI:FOREIGN-VARIABLE`)`
`(`SETF` (`FFI:FOREIGN-VALUE` `FFI:FOREIGN-VARIABLE`) ...)`

  This functions converts the reference to a C data structure which the `FFI:FOREIGN-VARIABLE` describes, to Lisp. Such a reference is typically obtained from `FFI:ALLOCATE-SHALLOW`, `FFI:ALLOCATE-DEEP`, `FFI:FOREIGN-ALLOCATE` or via a `(FFI:C-POINTER `c-type`)` C type description. Alternatively, macros like `FFI:WITH-C-PLACE` or `FFI:WITH-C-VAR` and the concept of foreign place hide many uses of this function.

  The `SETF` form performs conversion from Lisp to C, following to the `FFI:FOREIGN-VARIABLE`'s type description.

`(`FFI:WITH-FOREIGN-STRING` (`foreign-address` `char-count` `byte-count` `string` `&KEY` `encoding` `null-terminated-p` `start` `end`) `&BODY` `body`)`

  This forms converts a Lisp `string` according to the `encoding`, allocating space on the C execution stack. `encoding` can be any `EXT:ENCODING`, e.g. `CHARSET:UTF-16` or `CHARSET:UTF-8`, whereas `CUSTOM:*FOREIGN-ENCODING*` must be an ASCII-compatible encoding.

  `body` is then executed with the three variables `foreign-address`, `char-count` and `byte-count` respectively bound to an untyped `FFI:FOREIGN-ADDRESS` (as known from the FFI:C-POINTER foreign type specification) pointing to the stack location, the number of `CHARACTER`s of the Lisp `string` that were considered and the number of `(`UNSIGNED-BYTE` 8)` bytes that were allocated for it on the C stack.

  When `null-terminated-p` is true, which is the default, a variable number of zero bytes is appended, depending on the encoding, e.g. 2 for `CHARSET:UTF-16`, and accounted for in `byte-count`, and `char-count` is incremented by one.

  The `FFI:FOREIGN-ADDRESS` object bound to `foreign-address` is invalidated upon the exit from the form.

  A stupid example (a quite costly interface to `mblen`):

      (with-foreign-string (fv elems bytes string
                            :encoding charset:jis... :null-terminated-p nil
                            :end 5)
       (declare (ignore fv elems))
       (format t "This string would take ~D bytes." bytes))

`(`FFI:PARSE-C-TYPE` `c-type`)`
`(`FFI:DEPARSE-C-TYPE` `c-type-internal`)`

  Convert between the external (`LIST`) and internal (`VECTOR`) C type representations (used by `DESCRIBE`).

  ### Note

  Although you can memoize a `c-type-internal` (see Section 31.11.3, “Macro `EXT:MEMOIZED`” - but do not expect type redefinitions to work across memoization!), you cannot serialize it (write to disk) because deserialization loses object identity.

`(`FFI:ALLOCATE-SHALLOW` `c-type` `&KEY` `:COUNT` `:READ-ONLY`)`
`(`FFI:ALLOCATE-DEEP` `c-type` `contents` `&KEY` `:COUNT` `:READ-ONLY`)`
`(`FFI:FOREIGN-FREE` `foreign-entity` `&KEY` :FULL)`
`(`FFI:FOREIGN-ALLOCATE` `c-type-internal` `&KEY` :INITIAL-CONTENTS `:COUNT` `:READ-ONLY`)`

  Macro `FFI:ALLOCATE-SHALLOW` allocates `(`FFI:SIZEOF` `c-type`)` bytes on the C heap and zeroes them out (like `calloc`). When `:COUNT` is supplied, `c-type` is substituted with `(FFI:C-ARRAY `c-type` `count`)`, except when `c-type` is `CHARACTER`, in which case `(FFI:C-ARRAY-MAX `CHARACTER` `count`)` is used instead. When `:READ-ONLY` is supplied, the Lisp side is prevented from modifying the memory contents. This can be used as an indication that some foreign side is going to fill this memory (e.g. via `read`).

  Returns a `FFI:FOREIGN-VARIABLE` object of the actual `c-type`, whose address part points to the newly allocated memory.

  `FFI:ALLOCATE-DEEP` will call C `malloc` as many times as necessary to build a structure on the C heap of the given `c-type`, initialized from the given `contents`.

  E.g., `(`FFI:ALLOCATE-DEEP` 'FFI:C-STRING "ABCDE")` performs 2 allocations: one for a C pointer to a string, another for the contents of that string. This would be useful in conjunction with a char** C type declaration. `(`FFI:ALLOCATE-SHALLOW` 'FFI:C-STRING)` allocates room for a single pointer (probably 4 bytes).

  `(`FFI:ALLOCATE-DEEP` '`CHARACTER` "ABCDEF" :count 10)` allocates and initializes room for the type `(FFI:C-ARRAY-MAX `CHARACTER` 10)`, corresponding to char* or, more specifically, char[10] in C.

  Function `FFI:FOREIGN-FREE` deallocates memory at the address held by the given `foreign-entity`. If `:FULL` is supplied and the argument is of type `FFI:FOREIGN-VARIABLE`, recursively frees the whole complex structure pointed to by this variable.

  If given a `FFI:FOREIGN-FUNCTION` object that corresponds to a CLISP callback, deallocates it. Callbacks are automatically created each time you pass a Lisp function via the “FFI”.

  Use `(`SETF` `FFI:VALIDP`)` to disable further references to this address from Lisp. This is currently not done automatically. If the given pointer is already invalid, `FFI:FOREIGN-FREE` (currently) `SIGNAL`s an `ERROR`. This may change to make it easier to integrate with `EXT:FINALIZE`.

  Function `FFI:FOREIGN-ALLOCATE` is a lower-level interface as it requires an internal C type descriptor as returned by `FFI:PARSE-C-TYPE`.

`(`FFI:WITH-C-PLACE` (`variable` `foreign-entity`) `body`)`

  Create a place out of the given `FFI:FOREIGN-VARIABLE` object so operations on places (e.g. `FFI:CAST`, `FFI:DEREF`, `FFI:SLOT` etc.) can be used within `body`. `FFI:WITH-C-VAR` appears as a composition of `FFI:WITH-FOREIGN-OBJECT` and `FFI:WITH-C-PLACE`.

  Such a place can be used to access memory referenced by a `foreign-entity` object:

      (setq foo (allocate-deep '(c-array uint8 3) rgb))
      (with-c-place (place foo) (element place 0))

`FFI:*OUTPUT-C-FUNCTIONS*`
`FFI:*OUTPUT-C-VARIABLES*`
  CLISP will write the extern declarations for foreign functions (defined with `FFI:DEF-CALL-OUT`) and foreign variables (defined with `FFI:DEF-C-VAR`) into the output `#P".c"` (when the Lisp file is compiled with `COMPILE-FILE`) unless these variables are `NIL`. They are `NIL` by default, so the extern declarations are not written; you are encouraged to use `FFI:C-LINES` to include the appropriate C headers. Set these variables to non-`NIL` if the headers are not available or not usable.
`FFI:*FOREIGN-GUARD*`

  When this variable is non-`NIL` at compile time, CLISP will guard the C statements in the output file with cpp conditionals to take advantage of GNU autoconf feature detection. E.g.,

      (EVAL-WHEN (compile) (setq *foreign-guard* t))
      (FFI:DEF-CALL-OUT some-function (:name "function_name") ...)

  will produce

      # if defined(HAVE_FUNCTION_NAME)
        register_foreign_function((void*)&function_name,"function_name",1024);
      # endif

  and will compile and link on any system.

  This is mostly useful for product delivery when you want your module to build on any system even if some features will not be available.

  `FFI:*FOREIGN-GUARD*` is initialized to `NIL` for backwards compatibility.

`FFI:FOREIGN-POINTER-INFO`
  This is an interface to `dladdr` and it returns the 4 fields of Dl_info as multiple values.

Low-level “FFI” forms

`(`FFI:MEMORY-AS` `foreign-address` `c-type-internal` `&OPTIONAL` `offset`)`
`(`SETF` (`FFI:MEMORY-AS` `foreign-address` `c-type-internal` `&OPTIONAL` `offset`) `value`)`

  This accessor is useful when operating with untyped foreign pointers (`FFI:FOREIGN-ADDRESS`) as opposed to typed ones (represented by `FFI:FOREIGN-VARIABLE`). It allows to type and dereference the given pointer without the need to create an object of type `FFI:FOREIGN-VARIABLE`.

  Alternatively, one could use `(`FFI:FOREIGN-VALUE` (`FFI:FOREIGN-VARIABLE` `foreign-entity` `c-type-internal`))` (also `SETF`able).

  Note that `c-type-internal` is the internal representation of a foreign type, thus `FFI:PARSE-C-TYPE` is required with literal names or types, e.g. `(`FFI:MEMORY-AS` `foreign-address` (`FFI:PARSE-C-TYPE` '(FFI:C-ARRAY uint8 3)))` or `(`SETF` (`FFI:MEMORY-AS` `foreign-address` (`FFI:PARSE-C-TYPE` 'uint32)) 0)`.

### 32.3.3. (Foreign) C types

Foreign C types are used in the “FFI”. They are not regular Common Lisp types or CLOS classes.

A `c-type` is either a predefined C type or the name of a type defined by `FFI:DEF-C-TYPE`.

the predefined C types (`c-type`)

`simple-c-type`

  the simple C types

  Lisp name | Lisp equivalent | C equivalent | ILU equivalent | Comment
  --- | --- | --- | --- | ---
  `NIL` | `NIL` | void |  | as a result type only
  `BOOLEAN` | `BOOLEAN` | int | BOOLEAN |
  `CHARACTER` | `CHARACTER` | char | SHORT CHARACTER |
  char | `INTEGER` | signed char |  |
  uchar | `INTEGER` | unsigned char |  |
  short | `INTEGER` | short |  |
  ushort | `INTEGER` | unsigned short |  |
  int | `INTEGER` | int |  |
  uint | `INTEGER` | unsigned int |  |
  long | `INTEGER` | long |  |
  ulong | `INTEGER` | unsigned long |  |
  uint8 | `(`UNSIGNED-BYTE` 8)` | uint8 | BYTE |
  sint8 | `(`SIGNED-BYTE` 8)` | sint8 |  |
  uint16 | `(`UNSIGNED-BYTE` 16)` | uint16 | SHORT CARDINAL |
  sint16 | `(`SIGNED-BYTE` 16)` | sint16 | SHORT INTEGER |
  uint32 | `(`UNSIGNED-BYTE` 32)` | uint32 | CARDINAL |
  sint32 | `(`SIGNED-BYTE` 32)` | sint32 | INTEGER |
  uint64 | `(`UNSIGNED-BYTE` 64)` | uint64 | LONG CARDINAL | does not work on all platforms
  sint64 | `(`SIGNED-BYTE` 64)` | sint64 | LONG INTEGER | does not work on all platforms
  `SINGLE-FLOAT` | `SINGLE-FLOAT` | float |  |
  `DOUBLE-FLOAT` | `DOUBLE-FLOAT` | double |  |

FFI:C-POINTER
  This type corresponds to what C calls void*, an opaque pointer. When used as an argument, `NIL` is accepted as a FFI:C-POINTER and treated as `NULL`; when a function wants to return a `NULL` FFI:C-POINTER, it actually returns `NIL`.
`(FFI:C-POINTER `c-type`)`
  This type is equivalent to what C calls `c-type` *: a pointer to a single item of the given `c-type`. It differs from `(FFI:C-PTR-NULL `c-type`)` (see below) in that no conversion to and from Lisp will occur (beyond the usual one of the C `NULL` pointer to or from Lisp `NIL`). Instead, an object of type `FFI:FOREIGN-VARIABLE` is used to represent the foreign place. It is assimilable to a typed pointer.
FFI:C-STRING
  This type corresponds to what C calls char*, a zero-terminated string. Its Lisp equivalent is a string, without the trailing zero character.
`(FFI:C-STRUCT `class` (`ident1` `c-type1`) ... (`identn` `c-typen`))`

  This type is equivalent to what C calls struct { `c-type1` `ident1`; ...; `c-typen` `identn`; }. Its Lisp equivalent is: if `class` is `VECTOR`, a `SIMPLE-VECTOR`; if `class` is `LIST`, a proper list; if `class` is a symbol naming a structure or CLOS class, an instance of this class, with slots of names `ident1`, ..., `identn`.

  `class` may also be a `CONS` of a `SYMBOL` (as above) and a `LIST` of `FFI:DEF-C-STRUCT` options.

`(FFI:C-UNION (`ident1` `c-type1`) ... (`identn` `c-typen`))`
  This type is equivalent to what C calls union { `c-type1` `ident1`; ...; `c-typen` `identn`; }. Conversion to and from Lisp assumes that a value is to be viewed as being of `c-type1`.
`(FFI:C-ARRAY `c-type` `dim1`)`
`(FFI:C-ARRAY `c-type` (`dim1` ... `dimn`))`
  This type is equivalent to what C calls `c-type` [`dim1`] ... [`dimn`]. Note that when an array is passed as an argument to a function in C, it is actually passed as a pointer; you therefore have to write `(FFI:C-PTR (FFI:C-ARRAY ...))` for this argument's type.
`(FFI:C-ARRAY-MAX `c-type` `maxdimension`)`
  This type is equivalent to what C calls `c-type` [`maxdimension`], an array containing up to `maxdimension` elements. The array is zero-terminated if it contains less than `maxdimension` elements. Conversion from Lisp of an array with more than `maxdimension` elements silently ignores the extra elements.
`(FFI:C-FUNCTION (`:ARGUMENTS` {(`argument` `a-c-type` [`PARAM-MODE` [`ALLOCATION`]])}*) (`:RETURN-TYPE` `r-c-type` [`ALLOCATION`]) (`:LANGUAGE` `language`))`
  This type designates a C function that can be called according to the given prototype `(`r-c-type` (*) (`a-c-type1`, ...))`. Conversion between C functions and Lisp functions is transparent, and `NULL`/`NIL` is recognized and accepted.
`(FFI:C-PTR `c-type`)`
  This type is equivalent to what C calls `c-type` *: a pointer to a single item of the given `c-type`.
`(FFI:C-PTR-NULL `c-type`)`
  This type is also equivalent to what C calls `c-type` *: a pointer to a single item of the given `c-type`, with the exception that C `NULL` corresponds to Lisp `NIL`.
`(FFI:C-ARRAY-PTR `c-type`)`
  This type is equivalent to what C calls `c-type` (*)[]: a pointer to a zero-terminated array of items of the given `c-type`.

The conversion of FFI:C-STRING, `(FFI:C-ARRAY `CHARACTER` `dim1`)`, `(FFI:C-ARRAY-MAX `CHARACTER` `maxdimension`)`, `(FFI:C-ARRAY-PTR `CHARACTER`)` is governed by `CUSTOM:*FOREIGN-ENCODING*` and dimensions are given in bytes. The conversion of `CHARACTER`, and as such of `(FFI:C-PTR `CHARACTER`)`, or `(FFI:C-PTR-NULL `CHARACTER`)`, as well as that of multi-dimensional arrays `(FFI:C-ARRAY `CHARACTER` (`dim1` ... `dimn`))`, are governed by `CUSTOM:*FOREIGN-ENCODING*` if the latter is a “1:1” encoding, or by the ASCII encoding otherwise.

### Note

Remember that the C type char is a numeric type and does not use `CHARACTER` `EXT:ENCODING`s.

### 32.3.4. The choice of the C flavor

FFI:C-FUNCTION, `FFI:DEF-CALL-IN`, `FFI:DEF-CALL-OUT` take a `:LANGUAGE` argument. The `language` is either `:C` (denotes K&R C) or `:STDC` (denotes ANSI C) or `:STDC-STDCALL` (denotes ANSI C with the stdcall calling convention). It specifies whether the C function (caller or callee) has been compiled by a K&R C compiler or by an ANSI C compiler, and possibly the calling convention.

The default language is set using the macro `FFI:DEFAULT-FOREIGN-LANGUAGE` . If this macro has not been called in the current compilation unit (usually a file), a warning is issued and `:STDC` is used for the rest of the unit.

### 32.3.5. Foreign variables

Foreign variables are variables whose storage is allocated in the foreign language module. They can nevertheless be evaluated and modified through `SETQ`, just as normal variables can, except that the range of allowed values is limited according to the variable's foreign type.

### Equality of foreign values

For a foreign variable `x` the form `(`EQL` `x` `x`)` is not necessarily true, since every time `x` is evaluated its foreign value is converted to a fresh Lisp value. Ergo, `(`SETF` (`AREF` `x` `n`) `y`)` modifies this fresh Lisp value (immediately discarded), not the foreign data. Use `FFI:ELEMENT` et al instead, see Section 32.3.6, “Operations on foreign places”.

Foreign variables are defined using `FFI:DEF-C-VAR` and `FFI:WITH-C-VAR`.

### 32.3.6. Operations on foreign places

A `FFI:FOREIGN-VARIABLE` `name` defined by `FFI:DEF-C-VAR`, `FFI:WITH-C-VAR` or `FFI:WITH-C-PLACE` defines a place, i.e., a form which can also be used as argument to `SETF`. (An “lvalue” in C terminology.) The following operations are available on foreign places:

`FFI:ELEMENT` | `FFI:C-VAR-ADDRESS`
`FFI:DEREF` | `FFI:C-VAR-OBJECT`
`FFI:SLOT` | `FFI:TYPEOF`
`FFI:CAST` | `FFI:SIZEOF`
`FFI:OFFSET` | `FFI:BITSIZEOF`

### 32.3.7. Foreign functions

Foreign functions are functions which are defined in the foreign language. There are named foreign functions (imported via `FFI:DEF-CALL-OUT` or created via `FFI:DEF-CALL-IN`) and anonymous foreign functions; they arise through conversion of function pointers using `FFI:FOREIGN-FUNCTION`.

A call-out function is a foreign function called from Lisp: control flow temporarily leaves Lisp. A call-in function (AKA callback) is a Lisp function called from the foreign language: control flow temporary enters Lisp.

The following operators define foreign functions:

`FFI:DEF-CALL-IN`
`FFI:DEF-CALL-OUT`
`FFI:FOREIGN-FUNCTION`

#### 32.3.7.1. Callbacks and memory management

Callbacks (C function calling Lisp function) create so-called trampolines. A trampoline is a piece of C code which knows how to call a particular Lisp function. (That is how all foreign language interfaces work, not just ours). The C pointer that the foreign library receives is the pointer to this piece of code. These are not subject to garbage-collection, as there is no protocol to tell the garbage collector when a given callback is not needed anymore (unlike with Lisp objects).

With callbacks to named functions (i.e., created by a `FFI:DEF-CALL-IN` form where `function` is a function name) this is mostly harmless, since `function` is unlikely to be redefined.

With callbacks to anonymous functions (i.e., created by `FFI:FOREIGN-FUNCTION` or a `FFI:DEF-CALL-IN` form where `function` argument is a lambda expression), this might become an issue when they are produced dynamically and en masse, e.g. inside a loop, so that many trampolines are generated.

You can use `FFI:FOREIGN-FREE` to free the trampoline associated with a `FFI:FOREIGN-FUNCTION` object, but when you pass a lambda expression to a `FFI:DEF-CALL-OUT` as an argument of type FFI:C-FUNCTION, such a trampoline is allocated, but you do not get hold of the associated trampoline object, and thus you cannot (trivially) free it. Thus you may find it easier to create the `FFI:FOREIGN-FUNCTION` object first, pass it to the `FFI:DEF-CALL-OUT`, and then call `FFI:FOREIGN-FREE` manually.

### 32.3.8. Argument and result passing conventions

When passed to and from functions, allocation of arguments and results is handled as follows:

Values of `SIMPLE-C-TYPE`, FFI:C-POINTER are passed on the stack, with dynamic extent. The `ALLOCATION` is effectively ignored.

Values of type FFI:C-STRING, FFI:C-PTR, FFI:C-PTR-NULL, FFI:C-ARRAY-PTR need storage. The `ALLOCATION` specifies the allocation policy:

`:NONE`
  no storage is allocated.
`:ALLOCA`
  allocation of storage on the stack, which has dynamic extent.
`:MALLOC-FREE`
  storage will be allocated via `malloc` and released via `free`.

If no `ALLOCATION` is specified, the default `ALLOCATION` is `:NONE` for most types, but `:ALLOCA` for FFI:C-STRING and FFI:C-PTR and FFI:C-PTR-NULL and FFI:C-ARRAY-PTR and for `:OUT` arguments. The `:MALLOC-FREE` policy provides the ability to pass arbitrarily nested structures within a single conversion.

Call-out function arguments:

For arguments passed from Lisp to C:
  `:MALLOC-FREE`
    Lisp allocates the storage using `malloc` and never deallocates it. The C function is supposed to call `free` when done with it.
  `:ALLOCA`
    Lisp allocates the storage on the stack, with dynamic extent. It is freed when the C function returns.
  `:NONE`

    Lisp assumes that the pointer already points to a valid area of the proper size and puts the result value there.

    This is dangerous and deprecated.

For results passed from C to Lisp:
  `:MALLOC-FREE`
    Lisp calls `free` on it when done.
  `:NONE`
    Lisp does nothing.

Call-in function arguments:

For arguments passed from C to Lisp:
  `:MALLOC-FREE`
    Lisp calls `free` on it when done.
  `:ALLOCA`
  `:NONE`
    Lisp does nothing.
For results passed from Lisp to C:
  `:MALLOC-FREE`
    Lisp allocates the storage using `malloc` and never deallocates it. The C function is supposed to call `free` when done with it.
  `:NONE`

    Lisp assumes that the pointer already points to a valid area of the proper size and puts the result value there.

    This is dangerous and deprecated.

### Warning

Passing FFI:C-STRUCT, FFI:C-UNION, FFI:C-ARRAY, FFI:C-ARRAY-MAX values as arguments (not via pointers) is only possible to the extent the C compiler supports it. Most C compilers do it right, but some C compilers (such as gcc on hppa, x86_64 and Win32) have problems with this. The recommended workaround is to pass pointers; this is fully supported. See also clisp-devel (`Gmane/devel/10089`/https://sourceforge.net/p/clisp/mailman/message/12562038/).

### 32.3.9. Parameter Mode

A function parameter's `PARAM-MODE` may be

`:IN` (means: read-only):
  The caller passes information to the callee.
`:OUT` (means: write-only):
  The callee passes information back to the caller on return. When viewed as a Lisp function, there is no Lisp argument corresponding to this, instead it means an additional return value. Requires `ALLOCATION` = `:ALLOCA`.
`:IN-OUT` (means: read-write):
  Information is passed from the caller to the callee and then back to the caller. When viewed as a Lisp function, the `:OUT` value is returned as an additional return value.

The default is `:IN`.

### 32.3.10. Examples

List of Examples

32.2. Simple declarations and access
32.3. External C variable and some accesses
32.4. Calling an external function
32.5. Another example for calling an external function
32.6. Accessing cpp macros
32.7. Calling Lisp from C
32.8. Calling Lisp from C dynamically
32.9. Variable size arguments: calling `gethostname` from CLISP
32.10. Accessing variables in shared libraries
32.11. Controlling validity of resources
32.12. Floating point arrays

Example 32.2. Simple declarations and access

The C declaration

    struct foo {
      int a;
      struct foo * b[100];
    };

corresponds to

    (FFI:DEF-C-STRUCT foo
      (a int)
      (b (c-array (c-ptr foo) 100)))

The element access

    struct foo f;
    f.b[7].a

corresponds to

    (declare (type foo f))
    (foo-a (aref (foo-b f) 7)) 	; or
    (slot-value (aref (slot-value f 'b) 7) 'a)

Example 32.3. External C variable and some accesses

    struct bar {
      short x, y;
      char a, b;
      int z;
      struct bar * n;
    };

    extern struct bar * my_struct;

    my_struct->x++;
    my_struct->a = 5;
    my_struct = my_struct->n;

corresponds to

    (FFI:DEF-C-STRUCT bar
      (x short)
      (y short)
      (a char)
      (b char) 	; or (b character) if it represents a character, not a number
      (z int)
      (n (c-ptr bar)))

    (FFI:DEF-C-VAR my_struct (:type (c-ptr bar)))

    (setq my_struct (let ((s my_struct)) (incf (slot-value s 'x)) s)) 	; or
    (incf (slot my_struct 'x))
    (setq my_struct (let ((s my_struct)) (setf (slot-value s 'a) 5) s)) 	; or
    (setf (slot my_struct 'a) 5)
    (setq my_struct (slot-value my_struct 'n)) 	; or
    (setq my_struct (deref (slot my_struct 'n)))

Example 32.4. Calling an external function

On ANSI C systems, <`stdlib.h`> contains the declarations:

    typedef struct {
      int quot;   /* Quotient */
      int rem;    /* Remainder */
    } div_t;
    extern div_t div (int numer, int denom);

This translates to

    (FFI:DEF-C-STRUCT (div_t :typedef)
      (quot int)
      (rem int))
    (FFI:DEFAULT-FOREIGN-LANGUAGE :stdc)
    (FFI:DEF-CALL-OUT div (:ARGUMENTS (numer int) (denom int))
      (:RETURN-TYPE div_t))

Sample call from within Lisp (after running clisp-link):

    (div 20 3)
    ⇒ #S(DIV_T :QUOT 6 :REM 2)

Example 32.5. Another example for calling an external function

Suppose the following is defined in a file `cfun.c`:

    struct cfunr { int x; char *s; };
    struct cfunr * cfun (int i,char *s,struct cfunr * r,int a[10]) {
      int j;
      struct cfunr * r2;
      printf("i = %d\n", i);
      printf("s = %s\n", s);
      printf("r->x = %d\n", r->x);
      printf("r->s = %s\n", r->s);
      for (j = 0; j < 10; j++) printf("a[%d] = %d.\n", j, a[j]);
      r2 = (struct cfunr *) malloc (sizeof (struct cfunr));
      r2->x = i+5;
      r2->s = "A C string";
      return r2;
    }

It is possible to call this function from Lisp using the file `callcfun.lisp` (do not call it `cfun.lisp` - `COMPILE-FILE` will overwrite `cfun.c`) whose contents is:

    (DEFPACKAGE "TEST-C-CALL" (:use “COMMON-LISP” “FFI”))
    (IN-PACKAGE "TEST-C-CALL")
    (EVAL-WHEN (compile) (setq FFI:*OUTPUT-C-FUNCTIONS* t))
    (FFI:DEF-C-STRUCT cfunr (x int) (s c-string))
    (FFI:DEFAULT-FOREIGN-LANGUAGE :stdc)
    (FFI:DEF-CALL-OUT cfun (:RETURN-TYPE (c-ptr cfunr))
      (:ARGUMENTS (i int)
                  (s c-string)
                  (r (c-ptr cfunr) :in :alloca)
                  (a (c-ptr (c-array int 10)) :in :alloca)))
    (defun call-cfun ()
      (cfun 5 "A Lisp string" (make-cfunr :x 10 :s "Another Lisp string")
            '#(0 1 2 3 4 5 6 7 8 9)))

Use the module facility:

    $ clisp-link create cfun callcfun.c
    $ cc -O -c cfun.c
    $ cd cfun
    $ ln -s ../cfun.o cfun.o
    Add cfun.o to NEW_LIBS and NEW_FILES in link.sh.
    $ cd ..
    $ base/lisp.run -M base/lispinit.mem -c callcfun.lisp
    $ clisp-link add base base+cfun cfun
    $ base+cfun/lisp.run -M base+cfun/lispinit.mem -i callcfun
    > (test-c-call::call-cfun)
    i = 5
    s = A Lisp string
    r->x = 10
    r->s = Another Lisp string
    a[0] = 0.
    a[1] = 1.
    a[2] = 2.
    a[3] = 3.
    a[4] = 4.
    a[5] = 5.
    a[6] = 6.
    a[7] = 7.
    a[8] = 8.
    a[9] = 9.
    #S(TEST-C-CALL::CFUNR :X 10 :S "A C string")
    >
    $ rm -r base+cfun

Note that there is a memory leak here: The return value `r2` of `cfun()` is `malloc`ed but never `free`d. Specifying

    (:RETURN-TYPE (c-ptr cfunr) :malloc-free)

is not an alternative because this would also `free(r2->x)` but `r2->x` is a pointer to static data.

The memory leak can be avoided using

    (:RETURN-TYPE (c-pointer cfunr))

instead, in conjunction with

    (defun call-cfun ()
      (let ((data (cfun ...)))
        (UNWIND-PROTECT (FFI:FOREIGN-VALUE data)
          (FFI:FOREIGN-FREE data :FULL nil))))

Example 32.6. Accessing cpp macros

Suppose you are interfacing to a library `mylib.so` which defines types, macros and `inline` functions in `mylib.h`:

    #define FOO(x)  .....
    #define BAR ...
    struct zot { ... }
    inline int bar (int x) { ... }

To make them available from CLISP, write these forms into the lisp file `my.lisp`:

    (FFI:C-LINES "#include <mylib.h>
    int my_foo (int x) { return FOO(x); }
    int my_bar (int x) { return bar(x); }~%")
    (FFI:DEF-C-CONST bar)
    (FFI:DEF-C-CONST zot-size (:name "sizeof(struct zot)") (:guard nil))
    (FFI:DEF-CALL-OUT my-foo (:NAME "my_foo") (:ARGUMENTS (x ffi:int)) (:RETURN-TYPE ffi:int))
    (FFI:DEF-CALL-OUT my-bar (:NAME "my_bar") (:ARGUMENTS (x ffi:int)) (:RETURN-TYPE ffi:int))

Compiling this file will produce `my.c` and `my.fas` and you have two options:

1. Compile `my.c` into `my.o` with

       $ gcc -c my.c -lmylib

   and use clisp-link to create a new CLISP linking set.

2. Add `(`:LIBRARY` "my.dll")` to the `FFI:DEF-CALL-OUT` forms, compile `my.c` into `my.so` (or `my.dll` on Win32) with

       $ gcc -shared -o my.so my.c -lmylib

   and load `my.fas`.

Of course, you could have created `my1.c` containing

    #include <mylib.h>
    int my_foo (int x) { return FOO(x); }
    int my_bar (int x) { return bar(x); }

manually, but `FFI:C-LINES` allows you to keep the definitions of `my_foo` and `my-foo` close together for easier maintenance.

Example 32.7. Calling Lisp from C

To sort an array of double-floats using the Lisp function `SORT` instead of the C library function `qsort`, one can use the following interface code `sort1.c`. The main problem is to pass a variable-sized array.

    extern void lispsort_begin (int);
    void* lispsort_function;
    void lispsort_double (int n, double * array) {
      double * sorted_array;
      int i;
      lispsort_begin(n); /* store #'sort2 in lispsort_function */
      sorted_array = ((double * (*) (double *)) lispsort_function) (array);
      for (i = 0; i < n; i++) array[i] = sorted_array[i];
      free(sorted_array);
    }

This is accompanied by `sort2.lisp`:

    (DEFPACKAGE "FFI-TEST" (:use “COMMON-LISP” “FFI”))
    (IN-PACKAGE "FFI-TEST")
    (EVAL-WHEN (compile) (SETQ FFI:*OUTPUT-C-FUNCTIONS* t))
    (FFI:DEF-CALL-IN lispsort_begin (:ARGUMENTS (n int))
      (:RETURN-TYPE nil)
      (:LANGUAGE :stdc))
    (FFI:DEF-C-VAR lispsort_function (:type c-pointer))
    (DEFUN lispsort_begin (n)
      (SETF (FFI:CAST lispsort_function
                  `(FFI:C-FUNCTION
                     (:ARGUMENTS (v (c-ptr (c-array double-float ,n))))
                     (:RETURN-TYPE (c-ptr (c-array double-float ,n))
                                   :malloc-free)))
            #'sort2))
    (DEFUN sort2 (v)
      (declare (type vector v))
      (sort v #'<))

To test this, use the following test file `sorttest.lisp`:

    (EVAL-WHEN (compile) (setq FFI:*OUTPUT-C-FUNCTIONS* t))
    (FFI:DEF-CALL-OUT sort10
      (:NAME "lispsort_double")
      (:LANGUAGE :stdc)
      (:ARGUMENTS (n ffi:int)
                  (array (FFI:C-PTR (FFI:C-ARRAY ffi:double-float 10)) :in-out)))

Now try

    $ clisp-link create sort sort2.c sorttest.c
    $ cc -O -c sort1.c
    $ cd sort
    $ ln -s ../sort1.o sort1.o

Add `sort1.o` to `NEW_LIBS` and `NEW_FILES` in link.sh. Create a file `package.lisp` containing the form

    (MAKE-PACKAGE "FFI-TEST" :use '(“COMMON-LISP” “FFI”))

and add `package.lisp` to `TO_PRELOAD` in link.sh. Proceed:

    $ cd ..
    $ base/lisp.run -M base/lispinit.mem -c sort2.lisp -c sorttest.lisp
    $ clisp-link add base base+sort sort
    $ base+sort/lisp.run -M base+sort/lispinit.mem -i sort2 sorttest
    > (sort10 10 '#(0.501d0 0.528d0 0.615d0 0.550d0 0.711d0
                    0.523d0 0.585d0 0.670d0 0.271d0 0.063d0))
    #(0.063d0 0.271d0 0.501d0 0.523d0 0.528d0 0.55d0 0.585d0 0.615d0 0.67d0 0.711d0)
    $ rm -r base+sort

Example 32.8. Calling Lisp from C dynamically

Create a dynamic library `lispdll` (`#P".dll"` on Win32, `#P".so"` on UNIX) with the following function:

    typedef int (*LispFunc)(int parameter);
    int CallInFunc(LispFunc f) {
      return f(5)+11;
    }

and call it from Lisp:

    (ffi:def-call-out callout
      (:NAME "CallInFunc")
      (:LIBRARY "lispdll.dll")
      (:ARGUMENTS (function-arg
                   (FFI:C-FUNCTION (:ARGUMENTS (number ffi:int))
                                   (:RETURN-TYPE ffi:int) (:LANGUAGE :stdc))))
      (:RETURN-TYPE ffi:int)
      (:LANGUAGE :stdc))
    (defun f (x) (* x 2))
    ⇒ F
    (callout #'f)
    ⇒ 21

Example 32.9. Variable size arguments: calling `gethostname` from CLISP

The standard UNIX function

`int gethostname(` | char* name,
| size_t length`)`;

follows a typical pattern of C “out”-parameter convention: it expects a pointer to a buffer it is going to fill. So you must view this parameter as either `:OUT` or `:IN-OUT`. Additionally, one must tell the function the size of the buffer. Here `length` is just an `:IN` parameter. Sometimes this will be an `:IN-OUT` parameter, returning the number of bytes actually filled in.

So `name` is actually a pointer to an array of up to `length` characters, regardless of what the poor char* C prototype says, to be used like a C string (`NULL`-termination). UNIX specifies that “host names are limited to `HOST_NAME_MAX` bytes”, which is, of course, system dependent, but it appears that 256 is sufficient.

In the present example, you can use allocation `:ALLOCA`, like you would do in C: stack-allocate a temporary:

    (FFI:DEF-CALL-OUT gethostname
      (:ARGUMENTS (name (FFI:C-PTR (FFI:C-ARRAY-MAX ffi:char 256))
                        :OUT :ALLOCA)
                  (length ffi:int))
      (:LANGUAGE :stdc) (:LIBRARY :default)
      (:RETURN-TYPE ffi:int))
    ⇒ GETHOSTNAME
    (defun myhostname ()
      (multiple-value-bind (success name)	; :OUT and :IN-OUT parameters are returned as multiple values
          (gethostname 256)
        (if (zerop success) name
          (error "~S: ~S: ~S" 'myhostname (os:errno) (os:strerror)))))	; See Section 33.2.15, “Error handling”
    ⇒ MYHOSTNAME
    (myhostname)
    ⇒ #(97 98 97 122 111 110 107)

It is a `SIMPLE-VECTOR`, not a `STRING`, because the `name` argument is an array of char (an `INTEGER` type, see Section 32.3.3, “(Foreign) C types”), not character.

    (FFI:DEF-CALL-OUT gethostname
      (:ARGUMENTS (name (FFI:C-PTR (FFI:C-ARRAY-MAX character 256))
                        :OUT :ALLOCA)
                  (length ffi:int))
      (:LANGUAGE :stdc) (:LIBRARY :default)
      (:RETURN-TYPE ffi:int))
    ⇒ GETHOSTNAME
    (myhostname)
    ⇒ "abazonk"

Now we have a different problem: if `gethostname` fails, then the buffer allocated for `name` will be filled with garbage, but it will still go through the string conversion before we can check the `success` status. If `CUSTOM:*FOREIGN-ENCODING*` is `CHARSET:ISO-8859-1`, this is not a problem since no real conversion is happening, but with `CHARSET:UTF-8` an `ERROR` may be `SIGNAL`ed. A safe approach is to pass to the foreign function our own stack-allocated buffer, and only convert the buffer to a string when the foreign function succeeds:

    (FFI:DEF-CALL-OUT gethostname
      (:ARGUMENTS (name FFI:C-POINTER)
                  (length ffi:int))
      (:LANGUAGE :stdc) (:LIBRARY :default)
      (:RETURN-TYPE ffi:int))
    ⇒ GETHOSTNAME
    (defun myhostname ()
      (FFI:WITH-FOREIGN-OBJECT (name '(FFI:C-ARRAY-MAX character 256))
        (let ((success (gethostname name 256)))
          (if (zerop success) (FFI:FOREIGN-VALUE name)
            (error "~S: ~S: ~S" 'myhostname (os:errno) (os:strerror))))))
    ⇒ MYHOSTNAME
    (myhostname)
    ⇒ "abazonk"

Note that the `type` argument of `FFI:WITH-FOREIGN-OBJECT` is evaluated, so we do not have to make any assumptions about `HOST_NAME_MAX`:

    (defun myhostname ()
      (let ((host-name-max (os:sysconf :host-name-max)))
        (FFI:WITH-FOREIGN-OBJECT (name `(FFI:C-ARRAY-MAX character ,host-name-max))
          (let ((success (gethostname name host-name-max)))
            (if (zerop success) (FFI:FOREIGN-VALUE name)
              (error "~S: ~S: ~S" 'myhostname (os:errno) (os:strerror)))))))
    ⇒ MYHOSTNAME
    (myhostname)
    ⇒ "abazonk"

Example 32.10. Accessing variables in shared libraries

Suppose one wants to access and modify variables that reside in shared libraries:

    struct bar {
      double x, y;
      double out;
    };

    struct bar my_struct = {10.0, 20.5, 0.0};

    double test_dll(struct bar *ptr)
    {
      return ptr->out = ptr->out + ptr->x + ptr->y;
    }

This is compiled to `libtest.so` (or `libtest.dll`, depending on your platform).

Use the following lisp code:

    (USE-PACKAGE “FFI”)

    (FFI:DEF-C-STRUCT bar
      (x double-float)
      (y double-float)
      (out double-float))

    (FFI:DEF-CALL-OUT get-own-c-float
      (:LIBRARY "libtest.so")
      (:LANGUAGE :stdc)
      (:NAME "test_dll")
      (:ARGUMENTS (ptr c-pointer :in :alloca))
      (:RETURN-TYPE double-float))

    (FFI:DEF-C-VAR my-c-var (:name "my_struct")
      (:LIBRARY "libtest.so") (:type (c-ptr bar)))

Note that `get-own-c-float` takes a FFI:C-POINTER, not a `(FFI:C-PTR bar)` as the argument.

Now you can access call `get-own-c-float` on `my-c-var`:

    (FFI:C-VAR-ADDRESS my-c-var)
    ⇒ #<FOREIGN-ADDRESS #x282935D8>
    (get-own-c-float (FFI:C-VAR-ADDRESS my-c-var))
    ⇒ 30.5d0
    (get-own-c-float (FFI:C-VAR-ADDRESS my-c-var))
    ⇒ 61.0d0
    (get-own-c-float (FFI:C-VAR-ADDRESS my-c-var))
    ⇒ 91.5d0
    (get-own-c-float (FFI:C-VAR-ADDRESS my-c-var))
    ⇒ 122.0d0

Example 32.11. Controlling validity of resources

`FFI:SET-FOREIGN-POINTER` is useful in conjunction with `(`SETF` `FFI:VALIDP`)` to limit the extent of external resources. Closing twice can be avoided by checking `FFI:VALIDP`. All pointers depending on this resource can be disabled at once upon close by sharing their `FFI:FOREIGN-POINTER` using `FFI:SET-FOREIGN-POINTER`.

    (FFI:DEF-C-TYPE PGconn c-pointer)	; opaque pointer
    (FFI:DEF-CALL-OUT PQconnectdb (:RETURN-TYPE PGconn)
      (:ARGUMENTS (conninfo c-string)))
    (defun sql-connect (conninfo)
      (let ((conn (PQconnectdb conninfo)))
        (unless conn (error "NULL pointer"))
        ;; may wish to use EXT:FINALIZE as well
        (FFI:SET-FOREIGN-POINTER conn :COPY)))
    (defun sql-dependent-resource (conn arg1)
      (FFI:SET-FOREIGN-POINTER (PQxxx conn arg1) conn))
    (defun sql-close (connection)
      (when (FFI:VALIDP connection)
        (PQfinish connection)
        (setf (FFI:VALIDP connection) nil)
        T))

### Warning

Sharing `FFI:FOREIGN-POINTER` goes both ways: invalidating the dependent resource will invalidate the primary one.

### Note

An alternative approach to resource management, more suitable to non-“FFI” modules, is implemented in the `berkeley-db` module, see Section 33.7.2, “Closing handles”.

Example 32.12. Floating point arrays

Save this code into `sum.c`:

    double sum (int len, double *vec) {
      int i;
      double s=0;
      for (i=0; i<len; i++) s+= vec[i];
      return s;
    }

and compile it with

    $ gcc -shared -o libsum.so sum.c

Now you can sum doubles:

    (FFI:DEF-CALL-OUT sum (:NAME "sum") (:LIBRARY "libsum.so") (:LANGUAGE :stdc)
      (:RETURN-TYPE ffi:double-float)
      (:ARGUMENTS (len ffi:int) (vec (FFI:C-ARRAY-PTR ffi:double-float))))
    (sum 3 #(1d0 2d0 3d0))
    ⇒ 6d0

#### 32.3.10.1. More examples

You can find more information and examples of the CLISP “FFI” in the following clisp-list messages:

variable size values
  `Gmane/general/7278`/https://sourceforge.net/p/clisp/mailman/message/10143425/
variable length arrays
  `Gmane/general/6626`/https://sourceforge.net/p/clisp/mailman/message/10142276/ `Gmane/general/6628`/https://sourceforge.net/p/clisp/mailman/message/10142279/

Even more examples can be found in the file `tests/ffi.tst` in the CLISP source distribution.

## 32.4. Socket Streams

### Platform Dependent: UNIX, Win32 platforms only.

List of Examples

32.13. Lisp read-eval-print loop server
32.14. Lisp HTTP client

### 32.4.1. Introduction

List of Examples

32.13. Lisp read-eval-print loop server
32.14. Lisp HTTP client

Sockets are used for interprocess communications by processes running on the same host as well as by processes running on different hosts over a computer network. The most common kind of sockets is Internet stream sockets, and a high-level interface to them is described here. A more low level interface that closely follows the C system calls is also available, see Section 33.17, “Raw Socket Access”.

Two main varieties of sockets are interfaced to:

“active” sockets
  correspond to `SOCKET:SOCKET-STREAM`s which are bidirectional `STREAM`s
“passive” sockets
  correspond to `SOCKET:SOCKET-SERVER`s which are a special kind of objects that are used to allow the other side to initiate interaction with lisp.

Example 32.13. Lisp read-eval-print loop server

Here is a simple lisp read-eval-print loop server that waits for a remote connection and evaluates forms read from it:

    (LET ((server (SOCKET:SOCKET-SERVER)))
      (FORMAT t "~&Waiting for a connection on ~S:~D~%"
              (SOCKET:SOCKET-SERVER-HOST server) (SOCKET:SOCKET-SERVER-PORT server))
      (UNWIND-PROTECT
          ;; infinite loop, terminate with Control+C
          (LOOP (WITH-OPEN-STREAM (socket (SOCKET:SOCKET-ACCEPT server))
                  (MULTIPLE-VALUE-BIND (local-host local-port) (SOCKET:SOCKET-STREAM-LOCAL socket)
                    (MULTIPLE-VALUE-BIND (remote-host remote-port) (SOCKET:SOCKET-STREAM-PEER socket)
                      (FORMAT T "~&Connection: ~S:~D -- ~S:~D~%"
                              remote-host remote-port local-host local-port)))
                  ;; loop is terminated when the remote host closes the connection or on EXT:EXIT
                  (LOOP (WHEN (EQ :eof (SOCKET:SOCKET-STATUS (cons socket :input))) (RETURN))
                        (PRINT (EVAL (READ socket)) socket)
                        ;; flush everything left in socket
                        (LOOP :for c = (READ-CHAR-NO-HANG socket nil nil) :while c)
                        (TERPRI socket))))
        ;; make sure server is closed
        (SOCKET:SOCKET-SERVER-CLOSE server)))

### This opens a gaping security hole!

Functions like `EXT:SHELL`, `EXT:EXECUTE`, `EXT:RUN-SHELL-COMMAND` will allow the remote host to execute arbitrary code with your permissions. While functions defined in lisp (like `EXT:RUN-SHELL-COMMAND`) can be removed (using `FMAKUNBOUND`), the built-in functions (like `EXT:SHELL` and `EXT:EXECUTE`) cannot be permanently removed from the runtime, and an experienced hacker will be able to invoke them even if you `FMAKUNBOUND` their names.

You should limit the socket server to local connections by passing the `STRING` `"127.0.0.1"` as the `:INTERFACE` argument to `SOCKET:SOCKET-SERVER`.

Example 32.14. Lisp HTTP client

Here are a couple of simple lisp HTTP clients that fetch a web page and a binary file, and upload a file:

    (DEFUN wget-text (host page file &OPTIONAL (port 80))
      ;; HTTP requires the :DOS line terminator
      (WITH-OPEN-STREAM (socket (SOCKET:SOCKET-CONNECT port host :EXTERNAL-FORMAT :DOS))
         (FORMAT socket "GET ~A HTTP/1.0~2%" page)
         ;; dump the whole thing - header+data - into the output file
         (WITH-OPEN-FILE (out file :direction :output)
           (LOOP :for line = (READ-LINE socket nil nil) :while line
              :do (WRITE-LINE line out)))))
    (DEFUN wget-binary (host page file &OPTIONAL (port 80))
      (WITH-OPEN-STREAM (socket (SOCKET:SOCKET-CONNECT port host :EXTERNAL-FORMAT :DOS))
        (FORMAT socket "GET ~A HTTP/1.0~2%" page)
        (LOOP :with content-length :for line = (READ-LINE socket nil nil)
          ;; header is separated from the data with a blank line
          :until (ZEROP (LENGTH line)) :do
          (WHEN (STRING= line #1="Content-length: " :end1 #2=#.(LENGTH #1#))
            (SETQ content-length (PARSE-INTEGER line :start #2#))
          ;; this will not work if the server does not supply the content-length header
          :finally (RETURN (LET ((data (MAKE-ARRAY content-length
                                                   :element-type '(UNSIGNED-BYTE 8))))
                               ;; switch to binary i/o on socket
                               (SETF (STREAM-ELEMENT-TYPE socket) '(UNSIGNED-BYTE 8))
                               ;; read the whole file in one system call
                               (EXT:READ-BYTE-SEQUENCE data socket)
                               (WITH-OPEN-FILE (out file :direction :output
                                                    :ELEMENT-TYPE '(UNSIGNED-BYTE 8))
                                 ;; write the whole file in one system call
                                 (EXT:WRITE-BYTE-SEQUENCE data out))
                               data))))))
    (DEFUN wput (host page file &OPTIONAL (port 80))
      (WITH-OPEN-STREAM (socket (SOCKET:SOCKET-CONNECT port host :EXTERNAL-FORMAT :DOS))
        (WITH-OPEN-FILE (in file :direction :inptut :ELEMENT-TYPE '(UNSIGNED-BYTE 8))
          (LET* ((length (FILE-LENGTH in))
                 (data (MAKE-ARRAY length :element-type '(UNSIGNED-BYTE 8))))
            ;; some servers may not understand the "Content-length" header
            (FORMAT socket "PUT ~A HTTP/1.0~%Content-length: ~D~2%" page length)
            (SETF (STREAM-ELEMENT-TYPE socket) '(UNSIGNED-BYTE 8))
            (EXT:READ-BYTE-SEQUENCE data in)
            (EXT:WRITE-BYTE-SEQUENCE data socket)))
        ;; not necessary if the server understands the "Content-length" header
        (SOCKET:SOCKET-STREAM-SHUTDOWN socket :output)
        ;; get the server response
        (LOOP :for line = (READ-LINE socket nil nil) :while line :collect line)))

### 32.4.2. Socket API Reference

`(`SOCKET:SOCKET-SERVER` `&OPTIONAL` `port` `&KEY` `:INTERFACE` `:BACKLOG`)`

  This function creates a passive socket an binds a port to it. The server exists to watch for client connection attempts.

  The optional argument is the port to use (non-negative `FIXNUM`, `0` means assigned by the system).

  The `:BACKLOG` parameter defines maximum length of queue of pending connections (see `listen`) and defaults to 1.

  The `:INTERFACE` parameter specifies the interface(s) on which the socket server will listen, and is either a `STRING`, interpreted as the interface `IP` address that will be bound, or a socket, from whose peer the connections will be made.

  Default is (for backward compatibility) to bind to all local interfaces, but for security reasons it is advisable to bind to the loopback interface `"127.0.0.1"` if you need only local connections.

`(`SOCKET:SOCKET-SERVER-CLOSE` `socket-server`)`
  Closes down the server socket. Just like streams, `SOCKET:SOCKET-SERVER`s are closed at garbage-collection. You should not rely on this however, because garbage-collection times are not deterministic and the port assigned to the server socket cannot be reused until it is closed.
`(`SOCKET:SOCKET-SERVER-HOST` `socket-server`)`
`(`SOCKET:SOCKET-SERVER-PORT` `socket-server`)`
  Returns the host mask indicating which hosts can connect to this server and the port which was bound using `SOCKET:SOCKET-SERVER`.
`(`SOCKET:SOCKET-WAIT` `socket-server` `&OPTIONAL` [`seconds` [`microseconds`]])`
  Wait for a fixed time for a connection on the `socket-server` (a `SOCKET:SOCKET-SERVER`). Without a timeout argument, `SOCKET:SOCKET-WAIT` blocks indefinitely. When timeout is zero, poll. Returns `T` when a connection is available (i.e., `SOCKET:SOCKET-ACCEPT` will not block) and `NIL` on timeout.
`(`SOCKET:SOCKET-ACCEPT` `socket-server` `&KEY` `:ELEMENT-TYPE` `:EXTERNAL-FORMAT` `:BUFFERED` `:TIMEOUT`)`

  Waits for an attempt to connect to the `socket-server` and creates the server-side bidirectional `SOCKET:SOCKET-STREAM` for the connection.

  `SIGNAL`s an `ERROR` if no connection is made in that time.

`(`SOCKET:SOCKET-CONNECT` `port` `&OPTIONAL` [`host`] `&KEY` `:ELEMENT-TYPE` `:EXTERNAL-FORMAT` `:BUFFERED` `:TIMEOUT`)`

  Attempts to create a client-side bidirectional `SOCKET:SOCKET-STREAM`. Blocks until the server accepts the connection, for no more than `:TIMEOUT` seconds. If it is 0, returns immediately.

  `SIGNAL`s an `ERROR` if no connection could be established within the given time.

`(`SOCKET:SOCKET-STATUS` `socket-stream-or-list` `&OPTIONAL` [`seconds` [`microseconds`]])`

  Checks whether it is possible to read from or write to a `SOCKET:SOCKET-STREAM` or whether a connection is available on a `SOCKET:SOCKET-SERVER` without blocking.

  This is similar to `LISTEN`, which checks only one `STREAM` and only for input, and `SOCKET:SOCKET-WAIT`, which works only with `SOCKET:SOCKET-SERVER`s.

  We define `status` for a `SOCKET:SOCKET-SERVER` or a `SOCKET:SOCKET-STREAM` to be `:ERROR` if `select` finds an exceptional condition pending on any of the argument file descriptors.

  Additionally, for a `SOCKET:SOCKET-SERVER`, we define `status` to be `T` if a connection is available, i.e., is `SOCKET:SOCKET-ACCEPT` will not block, and `NIL` otherwise.

  Additionally, for a `SOCKET:SOCKET-STREAM`, we define `status` in the given `direction` (one of `:INPUT`, `:OUTPUT`, and `:IO`) to be

  Possible status values for various directions:

  `:INPUT` status: |
  `NIL` | reading will block
  `:INPUT` | some input is available
  `:EOF` | the stream has reached its end
  `:OUTPUT` status: |
  `NIL` | writing will block
  `:OUTPUT` | output to the stream will not block
  `:IO` status: |
  output status | input status
  --- | ---
  `NIL` | `:INPUT` | `:EOF`
  `NIL` | `NIL` | `:INPUT` | `:EOF`
  `:OUTPUT` | `:OUTPUT` | `:IO` | `:APPEND`

  Possible values of `socket-stream-or-list`:

  `SOCKET:SOCKET-STREAM` or `SOCKET:SOCKET-SERVER`
    Returns the appropriate status, as defined above (`:IO` status for `SOCKET:SOCKET-STREAM`)
  `(`SOCKET:SOCKET-STREAM` . `direction`)`
    Return the status in the specified direction
  a non-empty list of the above
    Return a list of values, one for each element of the argument list (a la `MAPCAR`)

  If you want to avoid consing[3] up a fresh list, you can make the elements of `socket-stream-or-list` to be `(`socket-stream` `direction` . `x`)` or `(`socket-server` . `x`)`. Then `SOCKET:SOCKET-STATUS` will destructively modify its argument and replace `x` or `NIL` with the status and return the modified list. You can pass this modified list to `SOCKET:SOCKET-STATUS` again.

  The optional arguments specify the timeout. `NIL` means wait forever, `0` means poll.

  The second value returned is the number of objects with non-`NIL` status, i.e., “actionable” objects. `SOCKET:SOCKET-STATUS` returns either due to a timeout or when this number is positive, i.e., if the timeout was `NIL` and `SOCKET:SOCKET-STATUS` did return, then the second value is positive (this is the reason `NIL` is not treated as an empty `LIST`, but as an invalid argument).

  This is the interface to `select` (on some platforms, `poll`), so it will work on any CLISP `STREAM` which is based on a file descriptor, e.g., `EXT:*KEYBOARD-INPUT*` and file/pipe/socket `STREAM`s, as well as on raw sockets.

`(`SOCKET:SOCKET-STREAM-HOST` `socket-stream`)`
`(`SOCKET:SOCKET-STREAM-PORT` `socket-stream`)`
  These two functions return information about the `SOCKET:SOCKET-STREAM`.
`(`SOCKET:SOCKET-STREAM-PEER` `socket-stream` [`do-not-resolve-p`])`

  Given a `SOCKET:SOCKET-STREAM`, this function returns the name of the host on the opposite side of the connection and its port number; the server-side can use this to see who connected.

  When the optional second argument is non-`NIL`, the hostname resolution is disabled and just the `IP` address is returned, without the FQDN.

  The `socket-stream` argument can also be a raw socket.

`(`SOCKET:SOCKET-STREAM-LOCAL` `socket-stream` [`do-not-resolve-p`])`

  The dual to `SOCKET:SOCKET-STREAM-PEER` - same information, host name and port number, but for the local host. The difference from `SOCKET:SOCKET-STREAM-HOST` and `SOCKET:SOCKET-STREAM-PORT` is that this function asks the OS (and thus returns the correct trusted values) while the other two are just accessors to the internal data structure, and basically return the arguments given to the function which created the `socket-stream`.

  The `socket-stream` argument can also be a raw socket.

`(`SOCKET:SOCKET-STREAM-SHUTDOWN` `socket-stream` `direction`)`

  Some protocols provide for closing the connection in one `direction` using `shutdown`. This function provides an interface to this UNIX system call. `direction` should be `:INPUT` or `:OUTPUT`. Note that you should still call `CLOSE` after you are done with your `socket-stream`; this is best accomplished by using `WITH-OPEN-STREAM`.

  All `SOCKET:SOCKET-STREAM`s are bidirectional `STREAM`s (i.e., both `INPUT-STREAM-P` and `OUTPUT-STREAM-P` return `T` for them). `SOCKET:SOCKET-STREAM-SHUTDOWN` breaks this and turns its argument stream into an input `STREAM` (if `direction` is `:OUTPUT`) or output `STREAM` (if `direction` is `:INPUT`). Thus, the following important invariant is preserved: whenever

  - a `STREAM` is open (i.e., `OPEN-STREAM-P` returns `T`) and
  - a `STREAM` is an input `STREAM` (i.e., `INPUT-STREAM-P` returns `T`)

  the `STREAM` can be read from (e.g., with `READ-CHAR` or `READ-BYTE`).

  The `socket-stream` argument can also be a raw socket.

`(`SOCKET:SOCKET-OPTIONS` `socket-server` `&REST` {`option`}*)`

  Query and, optionally, set socket options using `getsockopt` and `setsockopt`. An `option` is a keyword, optionally followed by the new value. When the new value is not supplied, `setsockopt` is not called. For each option the old (or current, if new value was not supplied) value is returned. E.g., `(`SOCKET:SOCKET-OPTIONS` `socket-server` :SO-LINGER 1 :SO-RCVLOWAT)` returns 2 values: `NIL`, the old value of the `:SO-LINGER` option, and 1, the current value of the `:SO-RCVLOWAT` option.

  The `socket-stream` argument can also be a raw socket.

`(`EXT:STREAM-HANDLES` `stream`)`
  Return the input and output OS file descriptors of the `stream` as multiple values. See Section 33.17, “Raw Socket Access”.

### 32.4.3. Argument `:TIMEOUT`

The `:TIMEOUT` argument specifies the number of seconds to wait for an event. The value may be a

- a non-negative `REAL` or
- a `LIST` `(sec usec)` or
- a `CONS` cell `(sec . usec)`.

## 32.5. Multiple Threads of Execution

### Platform Dependent: Only in CLISP built with configure-time flag `--with-threads`.

### Warning

This functionality is experimental.

Use it at your own risk.

Discuss it on clisp-devel.

### 32.5.1. Introduction

CLISP uses the OS threads to implement multiple threads of execution. Two flavors are supported: POSIX and Win32. Both are preemptive.

All symbols are exported from the package “THREADS”, which has nicknames “MT” (for MultiThreading) and “MP” (for MultiProcessing). When this functionality is present, `*FEATURES*` contains the symbol `:MT`.

See also Section 35.8, “Garbage Collection and Multithreading”.

### 32.5.2. General principles

#### 32.5.2.1. Parallelizability

A program developed for a single-threaded world which shares no application objects with programs running in other threads must run fine, without problems.

Specfically: if, in a single-threaded world, execution of program A before program B produces semantically the same results as execution of program B before program A, then in a multithreaded world, it is possible to run A and B simultaneously in different threads, and the result will be the same as in the two single-threaded cases (A before B, or B before A).

Summary

- If A and B have no common objects, then the implementation ensures that the principle is fulfilled.
- If A and B share some objects, the implementation allows the programs to satisfy the principle with little effort.

#### 32.5.2.2. Special Variable Values

Every dynamic variable has a global value that can be shared across all MT:THREADs.

Bindings of dynamic variables (via `LET`/`LET*`/`MULTIPLE-VALUE-BIND`) are local to MT:THREADs, i.e. every `SYMBOL` has a different value cell in each MT:THREAD. `MT:SYMBOL-VALUE-THREAD` can be used to inspect and modify these thread local bindings.

Threads do not inherit dynamic bindings from the parent thread.

Example:

    (defvar *global* 1)	; create a Global Variable
    (defun thread-1 ()
       	; here *global* and (SYMBOL-VALUE *global*) will be 1 not 2!
      (setq *global* 5)	; change the Global Variable value
      (let ((*global* 10))	; Per-Thread Variable value is initialized
        (setq *global* 20)	; Per-Thread Variable value is changed
        	; Global Variable value is not accessible here (only via MT:SYMBOL-VALUE-THREAD)
        )
      (setq *global* 30))	; Global Variable value is modified again
    (let ((*global* 2))	; Per-Thread Variable value is initialized
      (MT:MAKE-THREAD #'thread-1))

#### 32.5.2.3. Packages

### Note

Locking discussed in this section has nothing to do with `EXT:PACKAGE-LOCK`.

`PACKAGE` objects have an internal MT:MUTEX and are locked by `INTERN` before adding a symbol (if `FIND-SYMBOL` fails). All modifications of internal package data are guarded by this MT:MUTEX.

While iterating over package symbols with `DO-SYMBOLS`, `DO-EXTERNAL-SYMBOLS`, `DO-ALL-SYMBOLS`, `WITH-PACKAGE-ITERATOR` or the `LOOP` for-as-package subclause the package being iterated over is also locked.

#### 32.5.2.4. CLOS

##### This information is likely to change in the near future

CLOS is not thread-safe. `DEFCLASS`, `DEFGENERIC`, `DEFMETHOD`, `DEFSTRUCT` modify CLOS without any locking and may interfere with each other.

It is recommended that all code is `LOAD`ed before any MT:THREADs are spawned.

#### 32.5.2.5. Hash Tables, Sequences, and other mutable objects

##### If you want to shoot yourself, it is your responsibility to wear armor.

Nothing is ever locked automatically (automatic locking will impose an unjustifiable penalty on `HASH-TABLE`s and `SEQUENCE`s local to threads), so the user must use locks when sharing `HASH-TABLE`s, `SEQUENCE`s and user-defined mutable objects between threads.

This approach is consistent with the usual Common Lisp approach:

| The consequences are undefined when code executed during an object-traversing operation destructively modifies the object in a way that might affect the ongoing traversal operation... |
| --[sec_3-6]

| If an object O1 is used as a key in a hash table H and is then visibly modified with regard to the equivalence test of H, then the consequences are unspecified if O1 is used as a key in further operations on H... |
| --[sec_18-1-2]

##### 32.5.2.5.1. `RANDOM` and `RANDOM-STATE`

`RANDOM` modifies a `RANDOM-STATE` without locking, which means that you cannot carelessly share such objects between threads. However, `*RANDOM-STATE*` is bound per-thread (see `MT:MAKE-THREAD` and `MT:*DEFAULT-SPECIAL-BINDINGS*`), i.e., each thread has its own value and thus `RANDOM` is thread-safe.

#### 32.5.2.6. Examples of thread-unsafe code

Here are some forms whose results are undefined if two threads evaluate them without locking:

    (INCF (GETHASH x global-ht 0))	; see Section 32.5.2.5, “Hash Tables, Sequences, and other   mutable objects”
    (SETF (AREF global-array ...) ...)	; ditto
    (DEFMETHOD generic-function (...) ...)	; see Section 32.5.2.4, “CLOS”

### Warning

The above code may result in a segfault!

This is the reason why the multithreading support is still experimental. However, if you do not share global `HASH-TABLE`s between your threads and define all your CLOS methods before spawning threads, multithreading should work fine.

### 32.5.3. Thread API reference

MT:THREAD

  The type of the object returned by `MT:MAKE-THREAD`.

  Each MT:THREAD represent a separate computation, executed in parallel to each other.

`(`MT:MAKE-THREAD` `function` `&KEY` `:NAME` :INITIAL-BINDINGS :CSTACK-SIZE :VSTACK-SIZE)`

  Start a new named MT:THREAD running `function`.

  `:INITIAL-BINDINGS`

    an association list of `(`symbol` . `form`)`. The `form`s are `EVAL`uated in the context of the new thread and `symbol`s are bound to the result in the thread before `function` is called. The default value is `MT:*DEFAULT-SPECIAL-BINDINGS*`.

    The main purpose of this argument is to initialize some global data that should not be shared between threads, e.g., `*RANDOM-STATE*`, `*READTABLE*`.

    When using `:INITIAL-BINDINGS` it is best to `CONS` the application-specific data in front of `MT:*DEFAULT-SPECIAL-BINDINGS*` or copy and modify it to fit the application needs.

    ### Note

    When the same `symbol` appears in this association list multiple times, the first occurrence determines the value.

  `:CSTACK-SIZE`
    the size in bytes of the control (C) stack. If 0, the value is decided by the OS.
  `:VSTACK-SIZE`
    the size of the CLISP `STACK` in objects. The default value is calculated based on the `-m` option used when CLISP was started. If 0, the value will be the same as that of the calling thread.

  If MT:THREAD creation fails (e.g., due to a lack of system memory), a `CONTROL-ERROR` is `SIGNAL`ed.

  Cf. `pthread_create`.

`(`MT:THREADP` `object`)`
  Check whether the object is of type MT:THREAD.
`(`MT:THREAD-YIELD` `thread`)`

  Relinquish the CPU. The `thread` is placed at the end of the run queue and another thread is scheduled to run.

  Cf. `sched_yield`.

`(`MT:THREAD-INTERRUPT` `thread` `&KEY` `:FUNCTION` `:OVERRIDE` `:ARGUMENTS`)`

  Interrupt the normal execution flow in `thread` and ask it to `APPLY` `function` to `arguments`.

  Use `(`MT:THREAD-INTERRUPT` `thread` `:FUNCTION` `NIL`)` to debug `thread` and `(`MT:THREAD-INTERRUPT` `thread` `:FUNCTION` `T`)` to terminate `thread`.

  The `:OVERRIDE` argument overrides `MT:WITH-DEFERRED-INTERRUPTS` and should be used with extreme care.

  Threads can only be interrupted at a point where the garbage-collection can run, see Section 35.8, “Garbage Collection and Multithreading”.

  Currently on Win32 blocking I/O cannot be interrupted. The interrupt will be handled after the call returns.

  ### Warning

  Thread may be interrupted inside `UNWIND-PROTECT`'s cleanup forms and on non-local exit from `function` - they may not execute entirely. In order to prevent this, `MT:WITH-DEFERRED-INTERRUPTS` is provided.

`(`MT:THREAD-NAME` `thread`)`
  Return the `name` of the `thread`.
`(`MT:THREAD-ACTIVE-P` `thread`)`

  Return `NIL` if the thread has already terminated and `T` otherwise.

  ### Warning

  By the time this function returns `T`, `thread` may have already terminated anyway.

`(`MT:CURRENT-THREAD`)`
  Return the MT:THREAD object encapsulating the caller.
`(`MT:LIST-THREADS`)`

  Return the `LIST` of all currently running MT:THREADs.

  ### Warning

  By the time this function returns, the set of actually running threads may have a single intersection with the return value - the `MT:CURRENT-THREAD`.

MT:MUTEX

  The type of the object return by `MT:MAKE-MUTEX`.

  This represents a lock, i.e., a way to prevent different threads from doing something at the same time, e.g., modifying the same object.

`(`MT:MUTEXP` `object`)`
  Check whether the object is of type MT:MUTEX.
`(`MT:MAKE-MUTEX` `&KEY` `:NAME` `:RECURSIVE-P`)`

  Create new MT:MUTEX object - not locked by any thread. `:NAME` should be a `STRING` describing the mutex (this really helps debugging deadlocks). When `RECURSIVE-P` is non-`NIL`, a recursive MT:MUTEX is created i.e., a thread can acquire the mutex repeatedly (and should, of course, release it for each successful acquisition).

  Cf. `pthread_mutex_init`.

`(`MT:MUTEX-NAME` `thread`)`
  Return the `name` of the MT:MUTEX.
`(`MT:MUTEX-LOCK` `mutex` `&KEY` `:TIMEOUT`)`

  Acquire the `mutex`. If `mutex` is locked by another thread, the call blocks and waits up to `:TIMEOUT` seconds. If `:TIMEOUT` is not specified, waits forever.

  Return `T` on a successful locking of `mutex`, and `NIL` on timeout.

  If the calling thread has already acquired `mutex`, then

  - if `mutex` is recursive, `T` is returned (for each recursive `MT:MUTEX-LOCK` there should be a separate `MT:MUTEX-UNLOCK`);
  - If `mutex` is non-recursive an `ERROR` is `SIGNAL`ed to avoid a deadlock.

  Cf. `pthread_mutex_lock`.

`(`MT:MUTEX-UNLOCK` `mutex`)`

  Release (unlock) `mutex`. If the calling thread is not locking `mutex`, an `ERROR` is `SIGNAL`ed.

  Cf. `pthread_mutex_unlock`.

`(`MT:MUTEX-OWNER` `mutex`)`

  Return the MT:THREAD that owns (locks) `mutex`, or `NIL` if `mutex` is not locked.

  ### Warning

  By the time this function returns the `mutex` ownership may have changed (unless the owner is the `MT:CURRENT-THREAD`). The function is mostly useful for debugging deadlocks.

`(`MT:MUTEX-RECURSIVE-P` `mutex`)`
  Return a indicator whether `mutex` is recursive.
`(`MT:WITH-MUTEX-LOCK` (`mutex`) `&BODY` `body`)`
  Execute `body` with `mutex` locked. Upon exit `mutex` is released. Return whatever `body` returns.
MT:EXEMPTION

  The type of the object returned by `MT:MAKE-EXEMPTION`. These correspond to the POSIX condition variables, see <`pthread.h`>.

  These objects allow broadcasting state from one MT:THREAD to the others.

`(`MT:EXEMPTIONP` `object`)`
  Check whether the object is of type MT:EXEMPTION.
`(`MT:MAKE-EXEMPTION` `&KEY` `:NAME`)`

  Create a new MT:EXEMPTION object. `:NAME` should be a `STRING` describing the exemption (this really helps debugging deadlocks).

  Cf. `pthread_cond_init`.

`(`MT:EXEMPTION-NAME` `exemption`)`
  Return the `name` of the `exemption`.
`(`MT:EXEMPTION-SIGNAL` `exemption`)`

  Signal `exemption` object, i.e. wake up a thread blocked on waiting for `exemption`.

  Cf. `pthread_cond_signal`.

`(`MT:EXEMPTION-WAIT` `exemption` `mutex` `&KEY` `:TIMEOUT` `:TEST`)`

  Wait for another MT:THREAD to call `MT:EXEMPTION-SIGNAL` or `MT:EXEMPTION-BROADCAST` on `exemption`. `mutex` should be locked by the caller; otherwise an `ERROR` is `SIGNAL`ed. The function releases the `mutex` and waits for `exemption`. On return `mutex` is acquired again.

  When using exemptions there is always a boolean `predicate` involving shared variables associated with each exemption wait that is true if the thread should proceed.

  The function waits up to `:TIMEOUT` seconds. If timeout is not specified, waits forever.

  Returns `T` if `exemption` was signaled and `NIL` on timeout.

  On POSIX it is possible to have spurious wakeups, i.e., this function may return `T` even though no thread called `MT:EXEMPTION-BROADCAST` or `MT:EXEMPTION-SIGNAL`. Therefore, a common idiom for using this function is: `(`LOOP` :until (`predicate`) :do (`MT:EXEMPTION-WAIT` `exemption` `mutex`))`

  The `:TEST` argument simplifies this. When supplied, `MT:EXEMPTION-WAIT` returns when either `:TEST` `predicate` is satisfied (always called while `mutex` is held) or when `:TIMEOUT` elapses. The above loop is equivalent to: `(`MT:EXEMPTION-WAIT` `exemption` `mutex` `:TEST` #'`predicate`)`. When `:TEST` is supplied, `MT:EXEMPTION-WAIT` returns `T` when `exemption` was signaled and `:TEST` `predicate` is satisfied and `NIL` on timeout.

  This is the preferred and most portable way to wait on an exemption.

  Cf. `pthread_cond_wait`.

`(`MT:EXEMPTION-BROADCAST` `exemption`)`

  Signal `exemption` to all threads waiting for it.

  Cf. `pthread_cond_broadcast`.

`(`MT:Y-OR-N-P-TIMEOUT` seconds default `&REST` `arguments`)`
`(`MT:YES-OR-NO-P-TIMEOUT` seconds default `&REST` `arguments`)`
  Similar to `Y-OR-N-P` and `YES-OR-NO-P`, but use `MT:WITH-TIMEOUT` to return `DEFAULT` when no reply is given within timeout seconds.
`(`MT:WITH-TIMEOUT` (seconds `&BODY` timeout-forms) `&BODY` `body`)`

  Execute `body`. If it does not finish for up to seconds, it is interrupted and `timeout-forms` are executed.

  Return the values of the last evaluated form in either `body` or `timeout-forms`.

  ### Warning

  Since on timeout the current thread is interrupted, special care may be needed for ensuring proper cleanup in `body`. See `MT:THREAD-INTERRUPT` and `MT:WITH-DEFERRED-INTERRUPTS`.

`(`SETF` (`MT:SYMBOL-VALUE-THREAD` `symbol` `thread`) `value`)`
`(`MT:SYMBOL-VALUE-THREAD` `symbol` `thread`)`
  Access or set the Per-Thread Variable value. When `thread` is `T`, use the `MT:CURRENT-THREAD`; if it is `NIL`, use the Global Variable binding. Returns two values: the `symbol` binding and an indicator: `NIL` if not bound in the `thread`, `T` if bound, and `SYMBOL` `MAKUNBOUND` if the Per-Thread Variable binding was removed with `MAKUNBOUND`.
`MT:*DEFAULT-SPECIAL-BINDINGS*`
  The default `:INITIAL-BINDINGS` argument of `MT:MAKE-THREAD`.
`(`MT:WITH-DEFERRED-INTERRUPTS` `&BODY` `body`)`

  Defer thread interrupts (but not thread preemption) while `body` is executed. If there is an interrupt while `body` is run, it is queued and will be executed after `body` finishes.

  ### Warning

  Care is needed if waiting or blocking in `body`, since there is no way to interrupt it (in case of a deadlock). The macro was added to avoid partial `UNWIND-PROTECT`'s cleanup forms evaluation in case they are interrupted with a non-local exit.

`(`MT:THREAD-JOIN` `thread` `&KEY` `:TIMEOUT`)`

  Wait for `thread` to terminate and return two values: `thread`'s multiple values as a `LIST` and a `BOOLEAN` indicator of whether `thread` finished normally or has been interrupted with `MT:THREAD-INTERRUPT`.

  This function uses `MT:EXEMPTION-WAIT` (and not `pthread_join`), so there are no resource leaks normally associated with this function.

  On timeout, return multiple values `NIL` and `:TIMEOUT`.

  This function can be used repeatedly on the same thread, so this is the usual way to access the return values of a finished thread.

## 32.6. Quickstarting delivery with CLISP

This section describes three ways to turn CLISP programs into executable programs, which can be started as quickly as executables written in other languages.

### 32.6.1. Summary

UNIX
  CLISP can act as a script interpreter.
Desktop environments such as KDE, Gnome, Mac OS X or Win32.
  Files created with CLISP can be associated with the CLISP executable so that clicking on them would make CLISP execute the appropriate code.
Linux kernel with `CONFIG_BINFMT_MISC=y`
  Associate the extensions `#P".fas"` and `#P".lisp"` with CLISP; then you can make the files executable and run them from the command line.

### Multi-file applications

These three techniques apply to a single `#P".lisp"` or `#P".fas"` file. If your application is made up of several `#P".lisp"` or `#P".fas"` files, you can simply concatenate them (using cat) into one file; the techniques then apply to that concatenated file.

### Lisp-less target

These three techniques assume that the target machine has CLISP pre-installed and thus you can deliver just your own application, not CLISP itself. If you want to deliver applications without assuming anything about your target box, you have to resort to creating executable memory images.

### 32.6.2. Scripting with CLISP

#### Platform Dependent: UNIX platform only.

On UNIX, a text file (`#P".fas"` or `#P".lisp"`) can be made executable by adding a first line of the form

    #!interpreter [interpreter-arguments]

and using chmod to make the file executable.

#### OS Requirements

CLISP can be used as a script interpreter under the following conditions:

- The `interpreter` must be the full pathname of clisp The recommended path is `/usr/local/bin/clisp`, and if CLISP is actually installed elsewhere, making `/usr/local/bin/clisp` be a symbolic link to the real clisp.
- The `interpreter` must be a real executable, not a script. Unfortunately, in the binary distributions of CLISP on Solaris, clisp is a shell script because a C compiler cannot be assumed to be installed on this platform. If you do have a C compiler installed, build CLISP from the source yourself; make install will install clisp as a real executable.

- On some platforms, the first line which specifies the interpreter is limited in length:

  - max. 80 characters on HP-UX,
  - max. 127 characters on Linux.

  Characters exceeding this limit are simply cut off by the system. At least 128 characters are accepted on Solaris, IRIX, AIX, OSF/1. There is no workaround: You have to keep the interpreter pathname and arguments short.

- On Solaris and HP-UX, only the first `interpreter-arg` is passed to the `interpreter`. In order to pass more than one option (for example, `-M` and `-C`) to CLISP, separate them with no-break spaces instead of normal spaces. (But the separator between `interpreter` and `interpreter-arguments` must still be a normal space!) CLISP will split the `interpreter-arguments` both at no-break spaces and at normal spaces.

#### How clisp handles `interpreter-arguments`.

Shebang. The UNIX Shebang interpreter directive consists of one `interpreter` path and one `interpreter-arguments` string. This means that if the script `"my-script.lisp"` starts with

    #!/usr/local/bin/clisp -C -M my-image.mem -L French

the OS will pass clisp the following two arguments:

1. `"-C -M my-image.mem -L French"`
2. `"./my-script.lisp"`

instead of the six arguments:

1. `"-C"`
2. `"-M"`
3. `"my-image.mem"`
4. `"-L"`
5. `"French"`
6. `"./my-script.lisp"`

that the similar command line would generate.

Argument Splitting. This means that clisp may need to split its first argument on spaces. In fact, clisp does split its first argument when it starts with a dash.

Scripts named with a leading dash. When executing a script named, say, `-leading dash.lisp`:

    $ "-leading dash.lisp" maybe with args

clisp receives as its first argument either an absolute path `"/home/you/bin/-leading dash.lisp"` or a relative path `"./-leading dash.lisp"` - either way it does not start with a dash and thus will not be split. If, however, the script is run like this:

    $ clisp "-leading dash.lisp" args

the file name argument `"-leading dash.lisp"` will be split into two arguments

1. `"-leading"`
2. `"dash.lisp"`

and will fail. There are two workarounds to this problem:

1. Do not use dash as the first character in the file name. clisp is not the only command that will have problems. Rename them:

       $ mv "./-leading dash.lisp" "something sensible.lisp"

2. Pass the relative path on the command line:

       $ clisp "./-leading dash.lisp" args

#### Script execution

- The script should contain Lisp forms, except in the `#!` line.
- The file is loaded normally, through the function `LOAD` (in particular, the name of the script file, which is `$0` in /bin/sh, can be found in `*LOAD-TRUENAME*` and `*LOAD-PATHNAME*`).
- Before it is loaded, the variable `EXT:*ARGS*` is bound to a `LIST` of `STRING`s, representing the arguments given to the Lisp script (i.e., `$1` in /bin/sh becomes `(`FIRST` `EXT:*ARGS*`)` etc).
- The standard UNIX i/o facilities (see <`stdio.h`>) are used: `*STANDARD-INPUT*` is bound to `stdin`, `*STANDARD-OUTPUT*` to `stdout`, and `*ERROR-OUTPUT*` to `stderr`. Note Section 25.2.11.1, “Scripting and `DRIBBLE`”.
- The continuable `ERROR`s will be turned into `WARNING`s (using `EXT:APPEASE-CERRORS`).
- Non-continuable `ERROR`s and Control+C interrupts will terminate the execution of the Lisp script with an error status (using `EXT:EXIT-ON-ERROR`).
- If you wish the script's contents to be compiled during loading, add `-C` to the `interpreter-arguments`.

#### If nothing works

Another, quite inferior, alternative is to put the following into a file:

    #!/bin/sh
    exec clisp <<EOF
    (lisp-form)
    (another-lisp-form)
    (yet-another-lisp-form)
    EOF

The problem with this approach is that the return values of each form will be printed to `*STANDARD-OUTPUT*`. Another problem is that no user input will be available.

### 32.6.3. Desktop Environments

#### Platform Dependent: Win32, Gnome, KDE, Mac OS X desktop platforms only.

### Notations

Although we use Win32-specific notation, these techniques work on other desktop environments as well.

There are two different ways to make CLISP “executables” on desktop platforms.

1. Associate the `#P".mem"` extension with c:\clisp\clisp.exe `-M` "%s".
2. Associate the `#P".fas"` extension with c:\clisp\clisp.exe `-i` "%s" Alternatively, you may want to have a function `main` in your `#P".fas"` files and associate the `#P".fas"` extension with c:\clisp\clisp.exe `-i` %s `-x` (main).

Then clicking on the compiled lisp file (with `#P".fas"` extension) will load the file (thus executing all the code in the file), while the clicking on a CLISP memory image (with `#P".mem"` extension) will start CLISP with the given memory image.

### Note

On Win32, CLISP is distributed with a file `src/install.bat`, which runs `src/install.lisp` to create a file `clisp.lnk` on your desktop and also associates `#P".fas"`, `#P".lisp"`, and `#P".mem"` files with CLISP.

### 32.6.4. Associating extensions with CLISP via kernel

#### Platform Dependent: Linux platforms only.

You have to build your kernel with `CONFIG_BINFMT_MISC=y` and `CONFIG_PROC_FS=y`. Then you will have a `/proc/sys/fs/binfmt_misc/` directory and you will be able to do (as `root`; you might want to put these lines into `/etc/rc.d/rc.local`):

    # echo ":CLISP:E::fas::/usr/local/bin/clisp:" >> /proc/sys/fs/binfmt_misc/register
    # echo ":CLISP:E::lisp::/usr/local/bin/clisp:" >> /proc/sys/fs/binfmt_misc/register

Then you can do the following:

    $ cat << EOF > hello.lisp
    (print "hello, world!")
    EOF
    $ clisp -c hello.lisp
    ;; Compiling file hello.lisp ...
    ;; Wrote file hello.fas
    0 errors, 0 warnings
    $ chmod +x hello.fas
    $ hello.fas

    "hello, world!"

Please read `/usr/src/linux/Documentation/binfmt_misc.txt` for details.

## 32.7. Shell, Pipes and Printing

This section describes how CLISP can invoke external executables and communicate with the resulting processes.

### 32.7.1. Shell

Platform Dependent: UNIX platform only.
  `(`EXT:EXECUTE` `program` `arg1` `arg2` ...)` executes an external program. Its name is `program` (a full pathname). It is given the `STRING`s `arg1`, `arg2`, ... as arguments.
Platform Dependent: UNIX, Win32 platforms only.

  `(`EXT:SHELL` [`command`])` calls the operating system's shell.

  `(`EXT:SHELL`)` calls the shell for interactive use.

  `(`EXT:SHELL` `command`)` calls the shell only for execution of the one given `command`, which can be a complex expression:

      (EXT:SHELL "for x in 1 2 3; do echo $x; done")
      1
      2
      3
      ⇒ NIL

  Platform Dependent: UNIX platform only.
    `EXT:EXECUTE` is called on the value of the environment variable `SHELL` if used interactively; /bin/sh -c `command` if used non-interactively.
  Platform Dependent: Win32 platform only.
    `CreateProcess` is called on `(`OR` `command` (`EXT:GETENV` `COMSPEC`))`
Platform Dependent: UNIX, Win32 platforms only.

  The functions `EXT:RUN-SHELL-COMMAND` and `EXT:RUN-PROGRAM` are the general interface to `EXT:SHELL` and the above:

  `(`EXT:RUN-SHELL-COMMAND` `command` `&KEY` `:MAY-EXEC` `:INDIRECTP` `:INPUT` `:OUTPUT` `:IF-OUTPUT-EXISTS` `:WAIT`)` runs a shell command (including shell built-in commands, like DIR on Win32 and for/do/done on UNIX).

  `(`EXT:RUN-PROGRAM` `program` `&KEY` `:MAY-EXEC` `:INDIRECTP` `:ARGUMENTS` `:INPUT` `:OUTPUT` `:IF-OUTPUT-EXISTS` `:WAIT`)` runs an external program.

  `command`
    the shell command.
  `program`
    the program. The directories listed in the environment variable `PATH` will be searched for it.
  `:ARGUMENTS`
    a list of arguments (`STRING`s) that are given to the program.
  `:INPUT`
    where the program's input is to come from: either `:TERMINAL` (`stdin`, the default) or `:STREAM` (a Lisp `STREAM` to be created) or a pathname designator (an input file) or `NIL` (no input at all).
  `:OUTPUT`
    where the program's output is to be sent to: either `:TERMINAL` (`stdout`, the default) or `:STREAM` (a Lisp `STREAM` to be created) or a pathname designator (an output file) or `NIL` (ignore the output).
  `:IF-OUTPUT-EXISTS`
    what to do if the `:OUTPUT` file already exists. The possible values are `:OVERWRITE`, `:APPEND`, `:ERROR`, with the same meaning as for `OPEN`. The default is `:OVERWRITE`.
  `:WAIT`
    whether to wait for program termination or not (this is useful when no i/o to the process is needed); the default is `T`, i.e., synchronous execution.
  `:MAY-EXEC`
    pass exec to the underlying shell (UNIX only).
  `:INDIRECTP`
    use a shell to run the command, e.g., `(`EXT:RUN-PROGRAM` "dir" :indirectp `T`)` will run the shell built-in command DIR. This argument defaults to `T` for `EXT:RUN-SHELL-COMMAND` and to `NIL` for `EXT:RUN-PROGRAM`. (Win32 only).

  If `:STREAM` was specified for `:INPUT` or `:OUTPUT`, a Lisp `STREAM` is returned. If `:STREAM` was specified for both `:INPUT` and `:OUTPUT`, three Lisp `STREAM`s are returned, as for the function `EXT:MAKE-PIPE-IO-STREAM`. Otherwise, the return value depends on the process termination status: if it exited on a signal or a core-dump, the signal number is returned as a negative `INTEGER`, else, if it ended normally with 0 exit status, `NIL` is returned; otherwise, the status is returned as a positive `INTEGER`.

  This use of `EXT:RUN-PROGRAM` can cause deadlocks, see `EXT:MAKE-PIPE-IO-STREAM`.

### 32.7.2. Pipes

Platform Dependent: UNIX, Win32 platforms only.
  `(`EXT:MAKE-PIPE-INPUT-STREAM` `command` `&KEY` `:ELEMENT-TYPE` `:EXTERNAL-FORMAT` `:BUFFERED`)`
    returns an input `STREAM` that will supply the output from the execution of the given operating system command.
  `(`EXT:MAKE-PIPE-OUTPUT-STREAM` `command` `&KEY` `:ELEMENT-TYPE` `:EXTERNAL-FORMAT` `:BUFFERED`)`
    returns an output `STREAM` that will pass its output as input to the execution of the given operating system command.
  `(`EXT:MAKE-PIPE-IO-STREAM` `command` `&KEY` `:ELEMENT-TYPE` `:EXTERNAL-FORMAT` `:BUFFERED`)`

    returns three values. The primary value is a bidirectional `STREAM` that will simultaneously pass its output as input to the execution of the given operating system command and supply the output from this command as input. The second and third value are the input `STREAM` and the output `STREAM` that make up the bidirectional `STREAM`, respectively.

    ### Warning

    These three streams must be closed individually, see CLOSE-CONSTRUCTED-STREAM:ARGUMENT-STREAM-ONLY.

    ### Warning

    Improper use of this function can lead to deadlocks. Use it at your own risk!

    A deadlock occurs if the command and your Lisp program either both try to read from each other at the same time or both try to write to each other at the same time.

    To avoid deadlocks, it is recommended that you fix a protocol between the command and your program and avoid any hidden buffering: use `READ-CHAR`, `READ-CHAR-NO-HANG`, `LISTEN`, `SOCKET:SOCKET-STATUS` instead of `READ-LINE` and `READ` on the input side, and complete every output operation by a `FINISH-OUTPUT`. The same precautions must apply to the called command as well.

### 32.7.3. Printing

The macro `EXT:WITH-OUTPUT-TO-PRINTER`:

    (EXT:WITH-OUTPUT-TO-PRINTER (variable [:EXTERNAL-FORMAT])
      {declaration}*
      {form}*)

binds the variable `variable` to an output `STREAM` that sends its output to the printer.

## 32.8. Operating System Environment

This section describes how to get information about the environment on the machine on which CLISP is running.

### 32.8.1. Operating System Identification

`(`EXT:OPERATING-SYSTEM-TYPE`)`

  Returns the operating system (kernel) name. The value is a string, similar to the result of `uname -s`. Possible values include: `Linux` (both on GNU/Linux and Android systems), `GNU/Hurd`, `GNU/kFreeBSD`, `Darwin` (on macOS systems), `FreeBSD`, `DragonFly`, `NetBSD`, `OpenBSD`, `CYGWIN`, `Haiku`, `IRIX`, `Minix`, `SunOS` (on Solaris systems), `AIX`, `Windows`, `HP-UX`. Other values are possible as well.

`(`EXT:OPERATING-SYSTEM-VERSION`)`

  Returns the operating system (kernel) version. The value is a string, similar to the result of `uname -r`.

### 32.8.2. Environment Variables

Most modern operating systems support environment variables that associate strings (“variables”) with other strings (“values”). These variables are somewhat similar to the `SPECIAL` variables in Common Lisp: their values are inherited by the processes from their parent process.

You can access your OS environment variables using the function `(`EXT:GETENV` `&OPTIONAL` `string`)`, where `string` is the name of the environment variable. When `string` is omitted or `NIL`, all the environment variables and their values are returned in an association list.

You can change the value of existing environment variables or create new ones using `(`SETF` (`EXT:GETENV` `string`) `new-value`)`.

Use `(`SETF` (`EXT:GETENV` `string`) `NIL`)` to remove an environment variable `string`.

## Chapter 33. Extensions Implemented as Modules

## 33.1. A System Definition Facility

This module offers a system definition facility (similar to make). It is based on `asdf` 3.2.0.

Additionally, it hooks into `REQUIRE` using `CUSTOM::*MODULE-PROVIDER-FUNCTIONS*`. This way, requiring a module causes `asdf` to load the corresponding system.

When this module is present, `*FEATURES*` contains the symbols

`:ASDF3.2`
`:ASDF3.1`
`:ASDF3`
`:ASDF2`
`:ASDF`
`:ASDF-PACKAGE-SYSTEM`

.

## 33.2. System Calls

The “POSIX” module makes some system calls available from lisp. Not all of these system calls are actually POSIX, so this package has a nickname “OS”. If the package prefix is not specified below, the symbol resides in this package.

This module is present in the base linking set by default.

When this module is present, `*FEATURES*` contains the symbol `:SYSCALLS`.

### 33.2.1. Networking

`(`POSIX:RESOLVE-HOST-IPADDR` `&OPTIONAL` `host`)`

  Returns the HOSTENT structure:

  `name`
    host name
  `aliases`
    `LIST` of aliases
  `addr-list`
    `LIST` of `IP` addresses as dotted quads (for IPv4) or coloned octets (for IPv6)
  `addrtype`
    `INTEGER` address type (IPv4 or IPv6)

  When `host` is omitted or `:DEFAULT`, return the data for the current host. When `host` is `NIL`, all the host database is returned as a list (this would be the contents of the `/etc/hosts` file on a UNIX system or `${windir}/system32/etc/hosts` on a Win32 system).

  This is an interface to `gethostent`, `gethostbyname`, and `gethostbyaddr`.

`(OS:SERVICE `&OPTIONAL` `service-name` `protocol`)`

  A convenience function for looking up a port given the service name, such as “WWW” or “FTP”. It returns the SERVICE structure (name, list of aliases, port, protocol) for the given `service-name` and `protocol`, or all services as a `LIST` if `service-name` is missing or `NIL`.

  This is an interface to `getservent`, `getservbyname`, and `getservbyport`.

### 33.2.2. File system

`(POSIX:FILE-STAT `pathname` `&OPTIONAL` `link-p`)`

  Return the FILE-STAT structure. `pathname` can be a `STREAM`, a `PATHNAME`, a `STRING` or a `NUMBER` (on a UNIX system, meaning file descriptor). The first slot of the structure returned is the string or the number on which `stat`, `fstat`, or `lstat` was called. The other slots are numbers, members of the struct stat:

  `dev`
    Device ID of device containing file.
  `ino`
    File serial number.
  `mode`
    Mode of file.
  `nlink`
    Number of hard links to the file.
  `uid`
    User ID of file.
  `gid`
    Group ID of file.
  `rdev`
    Device ID (if file is character or block special).
  `size`
    For regular files, the file size in bytes. For symbolic links, the length in bytes of the pathname contained in the symbolic link. For a shared memory object, the length in bytes. For a typed memory object, the length in bytes. For other file types, the use of this field is unspecified.
  `atime`
    universal time of last access.
  `mtime`
    universal time of last data modification.
  `ctime`
    universal time of last status change (on Win32 - creation time).
  `blksize`
    A file system-specific preferred I/O block size for this object. In some file system types, this may vary from file to file.
  `blocks`
    Number of blocks allocated for this object.

  All slots are read-only.

  If the system does not support a particular field (e.g., Win32 prior to 2000 does not have hard links), `NIL` (or the default, like 1 for the number of hard links for old Win32) is returned.

  ### Win32 platform only.

  Normally, one would expect `(POSIX:FILE-STAT "foo")` and `(POSIX:FILE-STAT (`OPEN` "foo"))` to return “similar” objects (`OPEN`ing a file changes its access time though). This is not the case on Win32, where `stat` works but `fstat` does not. Specifically, `fstat` requires an int argument of an unknown nature, and it is not clear how do deduce it from the Win32 file handle. Therefore, instead of always failing on open `FILE-STREAM` arguments, this function calls `GetFileInformationByHandle` and fills the FILE-STAT return value based on that.

`(POSIX:SET-FILE-STAT `pathname` `&KEY` :ATIME :MTIME :MODE :UID :GID)`
  Set some file attributes using `chmod`, `chown`, and `utime`.
`(POSIX:STAT-VFS `pathname`)`

  Return a STAT-VFS structure. `pathname` can be a `STREAM`, a `PATHNAME`, a `STRING` or a `NUMBER` (on a UNIX system, meaning file descriptor). The first slot of the structure returned is the string or the number on which `statvfs` or `fstatvfs` was called. The other slots are members of the struct statvfs:

  `bsize`
    File system block size.
  `frsize`
    Fundamental file system block size.
  `blocks`
    Total number of blocks on file system in units of `frsize`.
  `bfree`
    Total number of free blocks.
  `bavail`
    Number of free blocks available to non-privileged processes.
  `files`
    Total number of file serial numbers.
  `ffree`
    Total number of free file serial numbers.
  `favail`
    Number of file serial numbers available to non-privileged processes.
  `fsid`
    File system ID.
  `flag`
    List of platform-dependent values, such as `:READ-ONLY`.
  `namemax`
    Maximum filename length.
  `vol-name`
    Volume name (Win32 only).
  `fs-type`
    File system type (Win32 only).

  All slots are read-only.

`(POSIX:CHROOT `pathname`)`

  Change the apparent disk root directory for the current running process (and its children) using `chroot`.

  Unless the process has superuser privileges, the operation will probably fail with `EPERM`.

`(POSIX:FILE-TREE-WALK `pathname` `function` `&KEY` FD-LIMIT CHDIR DEPTH MOUNT PHYS)`

  For each object under `pathname` calls `function` with 5 arguments:

  1. the pathname of the object
  2. the FILE-STAT instance containing information on the object (or `NIL`, see below)

  3. a keyword giving additional information. Its value is one of the following:

     `:F`
       The object is a file.
     `:D`
       The object is a directory.
     `:DP`
       The object is a directory and subdirectories have been visited. (This condition shall only occur if the `:DEPTH` argument is non-`NIL`.)
     `:SL`
       The object is a symbolic link. (This condition shall only occur if the `PHYS` argument is non-`NIL`.)
     `:SLN`
       The object is a symbolic link that does not name an existing file. (This condition shall only occur if the `PHYS` argument is `NIL`.)
     `:DNR`
       The object is a directory that cannot be read. The fn function shall not be called for any of its descendants.
     `:NS`
       The `stat` function failed on the object because of lack of appropriate permission. The FILE-STAT argument is `NIL`. If `stat` fails for any other reason, and `ERROR` is `SIGNAL`ed.

  4. the offset of the object's filename in the pathname passed as the first argument to `function`.
  5. the depth relative to the root of the walk, where the root level is 0.

  As soon as `function` returns non-`NIL`, this function returns that value; if `function` always returns `NIL`, then this function also returns `NIL` when the file tree is exhausted.

  The `:FD-LIMIT` argument defaults to 5.

  If `:CHDIR` argument is non-`NIL`, the function shall change the current working directory to each directory as it reports files in that directory

  If `:DEPTH` argument is non-`NIL`, the function shall report all files in a directory before reporting the directory itself.

  If `:MOUNT` argument is non-`NIL`, the function shall only report files in the same file system as `pathname`.

  If `:PHYS` argument is non-`NIL`, the function shall perform a physical walk and shall not follow symbolic links.

  Calls `nftw`.

`(OS:FILE-INFO `pathname` `&OPTIONAL` all)`

  Return the FILE-INFO structure. `pathname` should be a pathname designator. The 7 slots are

  `attributes`
  `ctime`
  `atime`
  `wtime`
  `size`
  `name`
  `name-short`

  When `pathname` is wild, returns just the first match, unless the second (optional) argument is non-`NIL`, in which case a `LIST` of objects is returned, one for each match.

`(POSIX:STREAM-LOCK `stream` `lock-p` `&KEY` (:BLOCK `T`) (:SHARED `NIL`) (:START 0) (:END `NIL`))`

  Set or remove a file lock for the (portion of the) file associated with `stream`, depending on `lock-p`. When `block` is `NIL`, the call is non-blocking, and when locking fails, it returns `NIL`. When `shared` is non-`NIL`, then lock can be shared between several callers. Several processes can set a `shared` (i.e., read) lock, but only one can set an `exclusive` (i.e., write, or non-`shared`) lock. Uses `fcntl` or `LockFileEx`.

  ### Warning

  UNIX and Win32 differ on locking 0-length files: on Win32, two processes can have exclusive locks on it!

  ### Warning

  Win32 locks are mandatory: if you lock a file, others will not be able to open it!

  UNIX locks are usually advisory: a process is free to ignore it, but on some UNIX systems one can mount some file system with mandatory locks.

`(POSIX:WITH-STREAM-LOCK (`stream` `&REST` `options`) `&BODY` `body`)`
  Lock the `stream`, execute the `body`, unlock the `stream`. Pass `options` to `POSIX:STREAM-LOCK`.
`(`POSIX:STREAM-OPTIONS` `stream` `command` `&OPTIONAL` `value`)`

  Call `fcntl`, `command` can be `:FD` or `:FL`.

  When `value` is missing, the option is queried and the value is returned; if `value` is supplied, the option is set and no values are returned.

`(`POSIX:FILE-SIZE` `file`)`
`(`SETF` (`POSIX:FILE-SIZE` `file`) `size`)`

  Extend `FILE-LENGTH` to operate on pathname designators.

  Set the `size` of a `file` using `ftruncate` (if `file` is an open `FILE-STREAM`) or `truncate` (if `file` is a pathname designator).

  Use `SetFilePointerEx` and `SetEndOfFile` on Win32.

`(POSIX:MKNOD `pathname` `type` `mode`)`
  Create a special file using `mknod`. Use `:FIFO` to create pipes and `:SOCK` to create sockets.
`(POSIX:CONVERT-MODE `mode`)`
  Convert between numeric, (e.g., `0644`) and symbolic (e.g., `(:RUSR :WUSR :RGRP :ROTH)`) file modes.
`(POSIX:UMASK `mode`)`
  Change process mask using `umask`.
`(`POSIX:COPY-FILE` `source` `destination` `&KEY` :METHOD :PRESERVE :IF-EXISTS :IF-DOES-NOT-EXIST)`

  This is an interface to `symlink` (when `method` is `:SYMLINK`), `link` (when it is `:HARDLINK`), and `rename` (when it is `:RENAME`) system calls, as well as, you guessed it, a generic file copy utility (when `method` is `:COPY`).

  When `method` is `:HARDLINK-OR-COPY` and `link` fails (e.g., because the `source` and `destination` are on different devices), fall back to `:COPY`.

  Both `source` and `destination` may be wild, in which case `TRANSLATE-PATHNAME` is used.

  When `preserve` is non-`NIL`, try to duplicate the time, owner, and permission characteristics of each source file in the corresponding destination file, similar to cp -p.

  The meaning and defaults of `:IF-EXISTS` and `:IF-DOES-NOT-EXIST` are the same as in `OPEN`.

  The actual `destination` file created is `(`MERGE-PATHNAMES` `source` `destination`)` so that `(`POSIX:COPY-FILE` "foo" "dir/")` creates `"dir/foo"` and `(`POSIX:COPY-FILE` "foo.csv" "bar")` creates `"bar.csv"`. If you want to actually copy `"foo.csv"` to `"bar"`, do `(`POSIX:COPY-FILE` (`MAKE-PATHNAME` :name "foo.csv") "bar")`.

`(`POSIX:DUPLICATE-HANDLE` `fd1` `&OPTIONAL` `fd2`)`
  This is an interface to the `dup` system calls on UNIX systems and to `DuplicateHandle` system call on Win32.
`(OS:SHORTCUT-INFO `pathname`)`
  Return information about a Win32 shortcut (`#P".lnk"`) file contents in a SHORTCUT-INFO structure.
`(OS:MAKE-SHORTCUT `pathname` `&KEY` :WORKING-DIRECTORY :ARGUMENTS :SHOW-COMMAND :ICON :DESCRIPTION :HOT-KEY :PATH)`
  Create (or modify the properties of an existing one) a Win32 shortcut (`#P".lnk"`) file.
`(OS:FILE-PROPERTIES filename set `&KEY` :INITID `&ALLOW-OTHER-KEYS`)`

  Wrapper for the Win32 `IPropertyStorage` functionality.

  `filename`
    name of a compound file (where properties are stored) or (on NTFS) name of any file (properties are stored in the filesystem). For compound files on NTFS, file storage is preferred.
  `set`
    property set, either `:BUILT-IN` or `:USER-DEFINED`
  `:INITID` `init-id`
    set the `init-id`
  `specifier value`
    `specifier`

      the property specifier: an `INTEGER`, `KEYWORD`, `STRING` or a `LIST` of an `INTEGER` or a `KEYWORD` and a `STRING`.

      `INTEGER`
        a property identifier
      `KEYWORD`

        Predefined `KEYWORD` IDs are

        `:APPNAME` | `:CREATE-DTM` | `:LASTPRINTED` | `:SUBJECT`
        `:AUTHOR` | `:DOC-SECURITY` | `:LASTSAVE-DTM` | `:TEMPLATE`
        `:CHARCOUNT` | `:EDITTIME` | `:LOCALE` | `:THUMBNAIL`
        `:CODEPAGE` | `:KEYWORDS` | `:PAGECOUNT` | `:TITLE`
        `:COMMENTS` | `:LASTAUTHOR` | `:REVNUMBER` | `:WORDCOUNT`

      `STRING`
        string property specifier. If no match is found, the first ID >= init-id (which defaults to 2) is associated with the string and its value is replaced with new value.
      (`INTEGER`|`KEYWORD` `STRING`)
        the first element is used as a specifier, the string is associated with this ID.

    `value`

      the new value of the property, a suitable Lisp object, `NIL` or a `LIST` of a `KEYWORD` and the value itself. If `value` is `NIL`, no assignment is done. `:EMPTY` and `:NULL` correspond to the VT_EMPTY and VT_NULL data types. `KEYWORD` in the `LIST` specifies the desired type of the property being set. Supported types are

      `:BOOL` | `:I1` | `:LPWSTR` | `:UI4`
      `:BSTR` | `:I2` | `:R4` | `:UI8`
      `:DATE` | `:I4` | `:R8` | `:UINT`
      `:ERROR` | `:I8` | `:UI1` |
      `:FILETIME` | `:LPSTR` | `:UI2` |

      FILETIMEs are converted to/from the universal time format, while DATEs are not.

  Returns the property contents before assignment as multiple values.

`(OS:FILE-OWNER `filename`)`

  Return the owner of the file.

  Platform Dependent: UNIX, Win32 platforms only.

`(POSIX:MKSTEMP `filename` `&KEY` `:DIRECTION` `:ELEMENT-TYPE` `:EXTERNAL-FORMAT` `:BUFFERED`)`

  Calls `mkstemp`; returns a `FILE-STREAM`.

  `:DIRECTION` should allow output.

`(POSIX:MKDTEMP `filename`)`
  Calls `mkdtemp`; creates a new empty temporary directory and returns its namestring.
`(POSIX:SYNC `&OPTIONAL` `stream`)`
  Calls `fsync` (`FlushFileBuffers` on Win32) on the file descriptor associated with `stream`, or `sync` when `stream` is not supplied

### 33.2.3. Users and Groups

`(POSIX:USER-INFO `&OPTIONAL` `user`)`

  Return the USER-INFO structure (name, encoded password, UID, GID, full name, home directory, shell). `user` should be a `STRING` (`getpwnam` is used) or an `INTEGER` (`getpwuid` is used). When `user` is missing or `NIL`, return all users (using `getpwent`). When `user` is `:DEFAULT`, return the information about the current user (using `getlogin`).

  Platform Dependent: UNIX platform only.

`(POSIX:GROUP-INFO `&OPTIONAL` `group`)`

  Return the GROUP-INFO structure (name, GID, member `LIST`). `group` should be a `STRING` (`getgrnam` is used) or an `INTEGER` (`getgrgid` is used). When `group` is missing or `NIL`, return all groups (using `getgrent`).

  Platform Dependent: UNIX platform only.

`(POSIX:USER-SHELLS)`
  Call `getusershell`.
`(OS:GET-USER-SID `&OPTIONAL` `user`)`
  Call `LookupAccountName` on `user` or, if that is not supplied, call `OpenProcessToken`, `GetTokenInformation`, and then `ConvertSidToStringSid` on `User.Sid`.

### 33.2.4. System Information

`(POSIX:UNAME)`
  Return a structure describing the OS, derived from `uname`.
`(POSIX:SYSCONF `&OPTIONAL` `what`)`
`(POSIX:CONFSTR `&OPTIONAL` `what`)`
  Return the specified configuration parameter or a property list of all available parameters (when `what` is missing or `NIL`), by calling `sysconf` and `confstr` respectively.
`(POSIX:PATHCONF `pathname` `&OPTIONAL` `what`)`
  Return the specified configuration parameter or a property list of all available parameters (when `what` is missing or `NIL`), by calling `fpathconf` on open file streams and `pathconf` on all other pathname designators.
`(`POSIX:RLIMIT` `&OPTIONAL` `what`)`
  Return the current and the maximal limits as two values when `what` is specified or the property list of all available limits (as an RLIMIT structure) when `what` is missing or `NIL`, by calling `getrlimit`.
`(`SETF` (`POSIX:RLIMIT` `what`) (`VALUES` `cur` `max`))`
`(`SETF` (`POSIX:RLIMIT` `what`) `rlimit`)`
`(`SETF` (`POSIX:RLIMIT`) `rlimit-plist`)`

  Set the limits using `setrlimit`.

  1. In the first form, `cur` and `max` are numbers (or `NIL` for `RLIM_INFINITY`).
  2. In the second form, `rlimit` is an RLIMIT structure.
  3. In the third form, `rlimit-plist` is a property list, as returned by `(`POSIX:RLIMIT`)`.
`(`POSIX:USAGE` `&OPTIONAL` `what`)`
  Return the USAGE structure describing the resource usage of the thread, process, or its children, using `getrusage`. WHen `what` is missing or `NIL`, return all available data as a property list.
`(POSIX:BOGOMIPS)`
  Compute the BogoMips rating.
`(POSIX:LOADAVG `&OPTIONAL` percentp)`
  Return 1, 5, and 15 minute system load averages, retrieved by `getloadavg`. If the argument is specified and non-`NIL`, the values are returned as integer percentiles.
`(OS:SYSTEM-INFO)`
  Return Win32 system information in a SYSTEM-INFO structure.
`(OS:VERSION)`
  Return Win32 version information in a VERSION structure.
`(OS:MEMORY-STATUS)`
  Return Win32 memory status information in a MEMORY-STATUS structure.
`(OS:PHYSICAL-MEMORY)`

  Return 2 values: total and available physical memory.

  Platform Dependent: UNIX, Win32 platforms only.

`(OS:HOSTID)`
`(`SETF` (OS:HOSTID) `value`)`

  Call `gethostid` and return a (hopefully) universally unique `INTEGER` identifier of this machine.

  ### Warning

  On Linux this number appears to be the IPv4 32-bit address with the first 2 bytes and the last 2 bytes swapped:

      (RAWSOCK:CONVERT-ADDRESS :inet (os:hostid))
      ⇒ "7.3.192.168"
      (first (posix:hostent-addr-list (POSIX:RESOLVE-HOST-IPADDR :default)))
      ⇒ "192.168.7.3"

  This, of course, means that “universally unique” it is not.

  Superuser can also set host identifier using `SETF` which calls `sethostid`.

  Platform Dependent: UNIX, Win32 platforms only.

`(OS:DOMAINNAME)`
`(`SETF` (OS:DOMAINNAME) `domain`)`
  Call `getdomainname` and `setdomainname`.

### 33.2.5. Mathematical functions

We implement access to

`(`erf` `real`)`
`(`erfc` `real`)`
`(`j0` `real`)`
`(`j1` `real`)`
`(`jn` `integer` `real`)`
`(`y0` `real`)`
`(`y1` `real`)`
`(`yn` `integer` `real`)`
`(`tgamma` `real`)`
`(`lgamma` `real`)`

which compute the error functions, Bessel functions and Gamma.

These functions are required by the POSIX standard and should be declared in <`math.h`>.

### Warning

Please note that these functions do not provide lisp-style error handling and precision, and do all the computations at the `DOUBLE-FLOAT` level.

Function `(`ffs` `n`)` finds the first bit set. It is implemented in pure Lisp and supports `BIGNUM`s.

### 33.2.6. Encryption

`(POSIX:CRYPT `key` `salt`)`
  Call `crypt`, arguments are `STRING`s.
`(POSIX:ENCRYPT `block` `decrypt-p`)`
`(POSIX:SETKEY `key`)`
  Call `encrypt` and `setkey`, respectively. `block` and `key` are of type `(`VECTOR` (`UNSIGNED-BYTE` 8) 8)`. `decrypt-p` is `BOOLEAN`.

### 33.2.7. Syslog

`(POSIX:OPENLOG ident `&KEY` :PID :CONS :NDELAY :ODELAY :NOWAIT :FACILITY)`
  Calls `openlog`
`(POSIX:SETLOGMASK maskpri)`
  Calls `setlogmask`.
`(POSIX:SYSLOG severity facility `format-string` `&REST` `arguments`)`

  Calls `syslog` on `(`APPLY` `FORMAT` `NIL` `format-string` `arguments`)`.

  No `%` conversion is performed, you must do all formatting in Lisp.

`(POSIX:CLOSELOG)`
  Calls `closelog`.

### 33.2.8. Processes

`(OS:PROCESS-ID)`
  Return the process ID (on UNIX calls `getpid`, on Win32 calls `GetCurrentProcessId`)
`(OS:PRIORITY `pid` `&OPTIONAL` `what`)`
`(`SETF` (OS:PRIORITY `pid` `&OPTIONAL` `what`) priority)`

  Return or set the process priority, platform-dependent `INTEGER` or platform-independent `SYMBOL`, one of

  `:REALTIME` | `:NORMAL` | `:IDLE`
  `:HIGH` | `:BELOW-NORMAL` |
  `:ABOVE-NORMAL` | `:LOW` |

  On UNIX calls `getpriority` and `setpriority`, on Win32 calls `GetPriorityClass` and `SetPriorityClass`.

`(POSIX:KILL `pid` `signal`)`
  Calls `kill`.
`(POSIX:GETPPID)`
  Calls `getppid`.
`(POSIX:GETPGRP)`
  Calls `getpgrp`.
`(POSIX:SETPGRP)`
  Calls `setpgrp`; on non-POSIX systems where it requires 2 arguments (legacy BSD-style), it is called as `setpgrp(0,0)`.
`(POSIX:GETSID `pid`)`
  Calls `getsid`.
`(POSIX:SETSID)`
  Calls `setsid`.
`(POSIX:PGID `pid`)`
`(`SETF` (POSIX:PGID `pid`) `pgid`)`
  Call `getpgid` and `setpgid`.
`(POSIX:SETREUID ruid euid)`
  Call `setreuid`.
`(POSIX:SETREGID rgid egid)`
  Call `setregid`.
`(POSIX:UID)`
`(`SETF` (POSIX:UID) `uid`)`
  Call `getuid` and `setuid`.
`(POSIX:GID)`
`(`SETF` (POSIX:GID) `gid`)`
  Call `getgid` and `setgid`.
`(POSIX:EUID)`
`(`SETF` (POSIX:EUID) `uid`)`
  Call `geteuid` and `seteuid`.
`(POSIX:EGID)`
`(`SETF` (POSIX:EGID) `gid`)`
  Call `getegid` and `setegid`.
`(POSIX:GROUPS)`
`(`SETF` (POSIX:GROUPS) `list`)`
  Call `getgroups` and `setgroups`.
`(`POSIX:WAIT` `&KEY` :PID :USAGE :NOHANG :UNTRACED :STOPPED :EXITED :CONTINUED :NOWAIT)`

  Wait for termination of the child process `:PID` (or any child process if not specified).

  If `:NOHANG` is specifed, return `0` as the only value immediately if no child process has terminated.

  Otherwise, the first return value is the `pid` of the terminated child process.

  The second and third return values depend on the way the process terminated:

  2nd value = `:EXITED`
  3rd value = `exit status`
    if the child terminated normally, e.g., by calling `exit`.
  2nd value = `:SIGNALED`
  3rd value = `signal`
    if the child process was terminated by a `signal`.
  2nd value = `:STOPPED`
  3rd value = `signal`
    if the child process was stopped by delivery of a `signal`.
  2nd value = `:CONTINUED`
  3rd value = `NIL`
    if the child process has continued from a job control stop.
  2nd value = `NIL`
  3rd value = `number`
    if CLISP could not figure out what has happened. Please read your local `waitpid` manual and send us a patch.

  The fourth value is only returned if `:USAGE` is non-`NIL` and in that case it is a structure describing resource usage by the terminated process, similar to what `POSIX:USAGE` returns.

  To avoid race conditions, it is important to start your subprocesses and `POSIX:WAIT` for them inside the `body` of a `POSIX:WITH-SUBPROCESSES` form.

  Calls `waitpid` and (when the `:USAGE` argument is non-`NIL`) `wait4`.

`(`POSIX:WITH-SUBPROCESSES` `&BODY`)`
  Evaluate `body` while receiving signals from subprocesses; your `EXT:RUN-PROGRAM` and related `POSIX:WAIT` calls should be inside it.

### 33.2.9. Accounting

`(POSIX:ENDUTXENT)`
  Calls `endutxent`.
`(POSIX:GETUTXENT `&OPTIONAL` utmpx)`
  Calls `getutxent`, returns a `STRUCTURE-OBJECT` of type POSIX:UTMPX, which can be passed to subsequent calls to this function and re-used.
`(POSIX:GETUTXID id)`
  Calls `getutxid`, the argument is filled and returned.
`(POSIX:GETUTXLINE line)`
  Calls `getutxline`, the argument is filled and returned.
`(POSIX:PUTUTXLINE utmpx)`
  Calls `pututxline`, the argument is filled and returned.
`(POSIX:SETUTXENT)`
  Calls `setutxent`.

### 33.2.10. Time and Data Conversion

`(OS:STRING-TIME `format-string` `&OPTIONAL` `object` timezone)`
  - When `object` is a `STRING`, it is parsed into a universal time according to `format-string` by `strptime`.
  - When it is an `INTEGER`, it is formatted according to `format-string` by `strftime`. `object` defaults to `(`GET-UNIVERSAL-TIME`)`.
`(OS:GETDATE `string` `&OPTIONAL` timezone)`

  Parse the `string` into a universal time using `getdate`.

  If the the environment variable `DATEMSK` is not set when CLISP is invoked, CLISP sets it to point to the file `modules/syscalls/datemsk`, installed as `(`MERGE-PATHNAMES` "syscalls/datemsk" `CUSTOM:*LIB-DIRECTORY*`)`.

### 33.2.11. String comparision

Functions

`(OS:VERSION< `x1` `x2`)`
`(OS:VERSION<= `x1` `x2`)`
`(OS:VERSION> `x1` `x2`)`
`(OS:VERSION>= `x1` `x2`)`

compare two `STRING`s as version numbers (e.g., `"foo10"` is greater than `"foo9"`) using `strverscmp` and return a `BOOLEAN`.

Function `OS:VERSION-COMPARE` does the same but returns either `<`, `>` or `=`.

### 33.2.12. Wildcard Matching

Wildcards describe sets of file names; see “Pathname Matching Notation” for the syntax description.

`(POSIX:FNMATCH `pattern` `string` `&KEY` :PATHNAME :PERIOD :NOESCAPE (:CASE-SENSITIVE `T`))`. This function returns a non-`NIL` value if the `string` matches the `pattern` by calling `fnmatch`.

`(POSIX:FNMATCH-MATCHER `pattern`)`. This function is a valid value for `CUSTOM:*APROPOS-MATCHER*`.

### Note

These two functions used to reside in a separate package “WILDCARD”, which has been now deprecated.

### 33.2.13. XTerm

`(`POSIX:MAKE-XTERM-IO-STREAM` `&KEY` title xterm)` When running under the X Window System, you can create a bidirectional `STREAM`, which uses a new dedicated text window (created by the executable specified by the `:XTERM` argument which should be compatible with xterm and rxvt, i.e., accept options `-n`, `-T`, and `-e`) using the function `POSIX:MAKE-XTERM-IO-STREAM`:

    (SETQ *ERROR-OUTPUT*
          (SETQ *DEBUG-IO*
                (POSIX:MAKE-XTERM-IO-STREAM :title "clisp errors and debug")))

Platform Dependent: UNIX platform only.

### 33.2.14. Standard file input and output

We define the type FFI:file = `FFI:FOREIGN-POINTER` and the following functions:

`(`fopen` `filename` `mode`)`
`(`fdopen` fd `mode`)`
`(`freopen` `filename` `mode` `file`)`
`(`fclose` `file`)`
`(`fflush` `file`)`
`(`clearerr` `file`)`
`(`feof` `file`)`
`(`ferror` `file`)`
`(`fileno` `file`)`

call their namesakes defined in <`stdio.h`>.

Functions

`OS:FOPEN`
`OS:FDOPEN`
`OS:FREOPEN`
`OS:FCLOSE`
`OS:FFLUSH`
`OS:FILENO`

may `SIGNAL` an `ERROR`.

Return values

`OS:FOPEN`
`OS:FDOPEN`
  FFI:file = `FFI:FOREIGN-POINTER`
`OS:FREOPEN`
`OS:FCLOSE`
`OS:FFLUSH`
`OS:CLEARERR`
  no values (they modify their `file` argument in place)
`OS:FEOF`
`OS:FERROR`
  `BOOLEAN`
`OS:FILENO`
  `INTEGER` (file descriptor)

We also define 3 constants

`OS:STDIN`
`OS:STDOUT`
`OS:STDERR`

#### Rationale

Iterface to foreign libraries. This functionality can be used by “FFI” modules which interface to functions which use the C FILE* pointers. E.g., `postgresql` has a function `PQtrace` which expects a FILE* argument. You can use `OS:FOPEN` and `OS:FCLOSE` for that.

Bypass Common Lisp filename processing. You can also use this functionality to access files whose names are interpreted as wild by Common Lisp. E.g.,

    (LET ((file (posix:fopen "foo*" "r")))
      (UNWIND-PROTECT
          (WITH-OPEN-STREAM (s (EXT:MAKE-STREAM (posix:fileno file)))
            (READ-LINE s))
        (posix:fclose file)))

### 33.2.15. Error handling

To handle errors in foreign functions, the following four functions are provided:

`(POSIX:ERRNO `&OPTIONAL` `error-code`)`

  When `error-code` is supplied, `errno` is set (useful before a system call which sets `errno` as the only way to report an error).

  If `error-code` is a `NUMBER`, the corresponding `KEYWORD` is returned and vice versa.

  When `error-code` is not supplied, the current `errno` is returned as a keyword if possible, a number otherwise.

  When `error-code` is `T`, all known error codes are returned as an association list.

`(OS:LAST-ERROR `&OPTIONAL` `error-code`)`

  Just like `POSIX:ERRNO`, but uses `GetLastError` and `SetLastError` instead of `errno`.

  Platform Dependent: Win32 platform only.

`(POSIX:STRERROR `&OPTIONAL` `error-code`)`

  Return a string description of `error-code`. When `error-code` is not supplied, `errno` is used.

  This calls `strerror`.

`(OS:FORMAT-MESSAGE `&OPTIONAL` `error-code`)`

  Just like `POSIX:STRERROR`, but uses `FormatMessage` and `GetLastError`.

  Platform Dependent: Win32 platform only.

### 33.2.16. Miscellanea

`(OS:CLIPBOARD)`
`(`SETF` (OS:CLIPBOARD) `object`)`

  Get (using `GetClipboardData`) a set (using `SetClipboardData`) the windows clipboard.

  Return a `STRING`; convert `object` to a `STRING` using `PRINC-TO-STRING`.

  Platform Dependent: Win32 and Cygwin platforms only.

## 33.3. Internationalization of User Programs

### 33.3.1. The GNU gettext

GNU gettext is a set of functions, included in CLISP or the C library, which permit looking up translations of strings through message catalogs. It is also a set of tools which makes the translation maintenance easy for the translator and the program maintainer.

The GNU gettext functions are available in CLISP in the “I18N” package, which is `EXT:RE-EXPORT`ed from the “EXT” package.

This module is present in the base linking set by default.

When this module is present, `*FEATURES*` contains the symbol `:I18N`.

`(`I18N:GETTEXT` `MSGID` `&OPTIONAL` `DOMAIN` `CATEGORY`)`
  returns the translation of the message `MSGID`, in the given `DOMAIN`, depending on the given `CATEGORY`. `MSGID` should be an ASCII string, and is normally the English message.
`(`I18N:NGETTEXT` `MSGID` `msgid_plural` `n` `&OPTIONAL` `DOMAIN` `CATEGORY`)`
  returns the plural form of the translation for of `MSGID` and `n` in the given `DOMAIN`, depending on the given `CATEGORY`. `MSGID` and `msgid_plural` should be ASCII strings, and are normally the English singular and English plural variant of the message, respectively.

#### 33.3.1.1. Domain

The `DOMAIN` is a string identifier denoting the program that is requesting the translation. The pathname of the message catalog depends on the `DOMAIN`: usually it is located at `TEXTDOMAINDIR/l/LC_MESSAGES/domain.mo`, where `l` is the ISO 639-2 code of the language. The notion of `DOMAIN` allows several Lisp programs running in the same image to request translations independently of each other.

Function `I18N:TEXTDOMAIN`. `(`I18N:TEXTDOMAIN`)` is a place that returns the default `DOMAIN`, used when no `DOMAIN` argument is passed to the `I18N:GETTEXT` and `I18N:NGETTEXT` functions. It is `SETF`able. `(`SETF` `I18N:TEXTDOMAIN`)` is usually used during the startup phase of a program. Note that the default `DOMAIN` is not saved in a memory image. The use of `(`SETF` `I18N:TEXTDOMAIN`)` is recommended only for programs that are so simple that they will never need more than one `DOMAIN`.

Function `I18N:TEXTDOMAINDIR`. `(`I18N:TEXTDOMAINDIR` `DOMAIN`)` is a place that returns the base directory, called `TEXTDOMAINDIR` above, where the message catalogs for the given `DOMAIN` are assumed to be installed. It is `SETF`able. `(`SETF` `I18N:TEXTDOMAINDIR`)` is usually used during the startup phase of a program, and should be used because only the program knows where its message catalogs are installed. Note that the `TEXTDOMAINDIR`s are not saved in a memory image.

#### 33.3.1.2. Category

The `CATEGORY` argument of the `I18N:GETTEXT` and `I18N:NGETTEXT` functions denotes which `LOCALE` facet the result should depend on. The possible values are a platform-dependent subset of `:LC_ADDRESS`, `:LC_ALL`, `:LC_COLLATE`, `:LC_CTYPE`, `:LC_IDENTIFICATION`, `:LC_MEASUREMENT`, `:LC_MESSAGES`, `:LC_MONETARY`, `:LC_NAME`, `:LC_NUMERIC`, `:LC_PAPER`, `:LC_TELEPHONE`, `:LC_TIME` The use of these values is useful for users who have a character/time/collation/money handling set differently from the usual message handling. Note that when a `CATEGORY` argument is used, the message catalog location depends on the `CATEGORY`: it will be expected at `TEXTDOMAINDIR/ll/category/domain.mo`.

#### 33.3.1.3. Internationalization Example

A non-internationalized program simulating a restaurant dialogue might look as follows.

prog.lisp.

    (setq n (parse-integer (first EXT:*ARGS*)))

    (format t "~A~%" "'Your command, please?', asked the waiter.")

    (format t "~@?~%"
              (if (= n 1) "a piece of cake" "~D pieces of cake")
              n)

After being internationalized, all strings are wrapped in `I18N:GETTEXT` calls, and `I18N:NGETTEXT` is used for plurals. Also, `I18N:TEXTDOMAINDIR` is assigned a value; in our case, for simplicity, the current directory.

prog.lisp.

    (setf (textdomain) "prog")
    (setf (textdomaindir "prog") "./")

    (setq n (parse-integer (first EXT:*ARGS*)))

    (format t "~A~%"
              (gettext "'Your command, please?', asked the waiter."))

    (format t "~@?~%"
              (ngettext "a piece of cake" "~D pieces of cake" n)
              n)

For ease of reading, it is customary to define an abbreviation for the `I18N:GETTEXT` function. An underscore is customary.

prog.lisp.

    (setf (textdomaindir "prog") "./")
    (defun _ (msgid) (gettext msgid "prog"))

    (setq n (parse-integer (first EXT:*ARGS*)))

    (format t "~A~%"
              (_"'Your command, please?', asked the waiter."))

    (format t "~@?~%"
              (ngettext "a piece of cake" "~D pieces of cake" n "prog")
              n)

Now the program's maintainer creates a message catalog template through the command

    $ xgettext -o prog.pot prog.lisp

### Note

xgettext version 0.11 or higher is required here.

The message catalog template looks roughly like this.

prog.pot.

    msgid "'Your command, please?', asked the waiter."
    msgstr ""

    msgid "a piece of cake"
    msgid_plural "%d pieces of cake"
    msgstr[0] ""
    msgstr[1] ""

Then a French translator creates a French message catalog

prog.fr.po.

    msgid ""
    msgstr ""
    "Content-Type: text/plain; charset=ISO-8859-1\n"
    "Plural-Forms: nplurals=2; plural=(n > 1);\n"

    msgid "'Your command, please?', asked the waiter."
    msgstr "«Votre commande, s'il vous plait», dit le garçon."

    # Les gateaux allemands sont les meilleurs du monde.
    msgid "a piece of cake"
    msgid_plural "%d pieces of cake"
    msgstr[0] "un morceau de gateau"
    msgstr[1] "%d morceaux de gateau"

and sends it to the program's maintainer.

The program's maintainer compiles the catalog as follows:

    $ mkdir -p ./fr/LC_MESSAGES
    $ msgfmt -o ./fr/LC_MESSAGES/prog.mo prog.fr.po

When a user in a french `LOCALE` then runs the program

    $ clisp prog.lisp 2

she will get the output

        «Votre commande, s'il vous plait», dit le garçon.
        2 morceaux de gateau

### 33.3.2. Locale

`(`I18N:SET-LOCALE` `&OPTIONAL` `CATEGORY` `LOCALE`)`

  This is an interface to `setlocale`.

  When `LOCALE` is missing or `NIL`, return the current one.

  When `CATEGORY` is missing or `NIL`, return all categories as a `LIST`.

`(`I18N:LOCALE-CONV`)`

  This is an interface to `localeconv`.

  Returns a I18N:LOCALE-CONV structure.

`(`I18N:LANGUAGE-INFORMATION` `&OPTIONAL` `item`)`

  This is an interface to `nl_langinfo` (UNIX) and `GetLocaleInfo` (Win32).

  When `item` is missing or `NIL`, return all available information as a `LIST`.

## 33.4. POSIX Regular Expressions

List of Examples

33.1. `REGEXP:MATCH`
33.2. `REGEXP:REGEXP-QUOTE`
33.3. Count unix shell users

The “REGEXP” module implements the POSIX regular expressions matching by calling the standard C system facilities. The syntax of these regular expressions is described in many places, such as your local <`regex.h`> manual and Emacs info pages.

This module is present in the base linking set by default.

When this module is present, `*FEATURES*` contains the symbol `:REGEXP`.

Regular Expression API

`(`REGEXP:MATCH` `pattern` `string` `&KEY` (`:START` 0) `:END` `:EXTENDED` `:IGNORE-CASE` `:NEWLINE` `:NOSUB` `:NOTBOL` `:NOTEOL`)`

  This macro returns as first value a `REGEXP:MATCH` structure containing the indices of the start and end of the first match for the regular expression `pattern` in `string`; or no values if there is no match. Additionally, a `REGEXP:MATCH` structure is returned for every matched `"\(...\)"` group in `pattern`, in the order that the open parentheses appear in `pattern`. If `start` is non-`NIL`, the search starts at that index in `string`. If `end` is non-`NIL`, only `(`SUBSEQ` `string` `start` `end`)` is considered.

  Example 33.1. `REGEXP:MATCH`

      (REGEXP:MATCH "quick" "The quick brown fox jumped quickly.")
      ⇒ #S(REGEXP:MATCH :START 4 :END 9)
      (REGEXP:MATCH "quick" "The quick brown fox jumped quickly." :start 8)
      ⇒ #S(REGEXP:MATCH :START 27 :END 32)
      (REGEXP:MATCH "quick" "The quick brown fox jumped quickly." :start 8 :end 30)
      ⇒ NIL
      (REGEXP:MATCH "\\([a-z]*\\)[0-9]*\\(bar\\)" "foo12bar")
      ⇒ #S(REGEXP:MATCH :START 0 :END 8) ;
      ⇒ #S(REGEXP:MATCH :START 0 :END 3) ;
      ⇒ #S(REGEXP:MATCH :START 5 :END 8)

`(`REGEXP:MATCH-START` `match`)`
`(`REGEXP:MATCH-END` `match`)`
  Return the start and end the `match`; `SETF`-able.
`(`REGEXP:MATCH-STRING` `string` `match`)`
  Extracts the substring of `string` corresponding to the given pair of start and end indices of `match`. The result is shared with `string`. If you want a fresh `STRING`, use `COPY-SEQ` or `COERCE` to `SIMPLE-STRING`.
`(`REGEXP:REGEXP-QUOTE` `string` `&OPTIONAL` `extended`)`

  This function returns a regular expression `STRING` that matches exactly `string` and nothing else. This allows you to request an exact string match when calling a function that wants a regular expression.

  Example 33.2. `REGEXP:REGEXP-QUOTE`

      (regexp-quote "^The cat$")
      ⇒ "\\^The cat\\$"

  One use of `REGEXP:REGEXP-QUOTE` is to combine an exact string match with context described as a regular expression. When `extended` is non-`NIL`, also quote #\+ and #\?.

`(`REGEXP:REGEXP-COMPILE` `string` `&KEY` `:EXTENDED` `:IGNORE-CASE` `:NEWLINE` `:NOSUB`)`
  Compile the regular expression `string` into an object suitable for `REGEXP:REGEXP-EXEC`.
`(`REGEXP:REGEXP-EXEC` `pattern` `string` `&KEY` `:RETURN-TYPE` (`:START` 0) `:END` `:NOTBOL` `:NOTEOL`)`

  Execute the `pattern`, which must be a compiled regular expression returned by `REGEXP:REGEXP-COMPILE`, against the appropriate portion of the `string`.

  Returns `REGEXP:MATCH` structures as multiple values (one for each subexpression which successfully matched and one for the whole pattern).

  If `:RETURN-TYPE` is `LIST` (or `VECTOR`), the `REGEXP:MATCH` structures are returned as a `LIST` (or a `VECTOR`) instead. Also, if there are more than `MULTIPLE-VALUES-LIMIT` `REGEXP:MATCH` structures to return, a `LIST` is returned instead of multiple values. If `:RETURN-TYPE` is `BOOLEAN`, return `T` or `NIL` as an indicator of success or failure, but do not allocate anything.

`(`REGEXP:REGEXP-SPLIT` `pattern` `string` `&KEY` (`:START` 0) `:END` `:EXTENDED` `:IGNORE-CASE` `:NEWLINE` `:NOSUB` `:NOTBOL` `:NOTEOL`)`
  Return a list of substrings of `string` (all sharing the structure with `string`) separated by `pattern` (a regular expression `STRING` or a return value of `REGEXP:REGEXP-COMPILE`)
`(`REGEXP:WITH-LOOP-SPLIT` (`variable` `stream` `pattern` `&KEY` (`:START` 0) `:END` `:EXTENDED` `:IGNORE-CASE` `:NEWLINE` `:NOSUB` `:NOTBOL` `:NOTEOL`) `&BODY` `body`)`
  Read lines from `stream`, split them with `REGEXP:REGEXP-SPLIT` on `pattern`, and bind the resulting list to `variable`.
`:EXTENDED` `:IGNORE-CASE` `:NEWLINE` `:NOSUB`
  These options control compilation of a pattern. See <`regex.h`> for their meaning.
`:NOTBOL` `:NOTEOL`
  These options control execution of a pattern. See <`regex.h`> for their meaning.
`REGEXP:REGEXP-MATCHER`
  A valid value for `CUSTOM:*APROPOS-MATCHER*`. This will work only when your `LOCALE` is `CHARSET:UTF-8` because CLISP uses `CHARSET:UTF-8` internally and POSIX constrains <`regex.h`> to use the current `LOCALE`.

Example 33.3. Count unix shell users

The following code computes the number of people who use a particular shell:

    #!/usr/bin/clisp -C
    (USE-PACKAGE "REGEXP")
    (let ((h (make-hash-table :test #'equal :size 10)) (n 0))
      (with-open-file (f (or (first EXT:*ARGS*) "/etc/passwd"))
        (with-loop-split (s f (s f (or (second EXT:*ARGS*) ":")))
          (incf (gethash (seventh s) h 0))))
      (with-hash-table-iterator (i h)
        (loop (multiple-value-bind (r k v) (i)
                (unless r (return))
                (format t "[~d] ~s~30t== ~5:d~%" (incf n) k v)))))

For comparison, the same (almost - except for the nice output formatting) can be done by the following Perl:

    #!/usr/bin/perl -w

    use diagnostics;
    use strict;

    my $IN = $ARGV[0] || "/etc/passwd";
    open(INF,"≤ $IN") or die "$0: cannot read file [$IN]: $!\n";
    my %hash;
    while (≤INF≥) {
      chop;
      my @all = split($ARGV[1] || ":");
      $hash{$all[6] || ""}++;
    }
    my $ii = 0;
    for my $kk (keys(%hash)) {
      print "[",++$ii,"] \"",$kk,"\"  -- ",$hash{$kk},"\n";
    }
    close(INF);

## 33.5. Advanced Readline and History Functionality

The “READLINE” module exports most of the GNU readline functions using “FFI”.

This module is present even in the base linking set by default on platforms where both GNU readline and “FFI” are available.

When this module is present, `*FEATURES*` contains the symbol `:READLINE`.

See `modules/readline/test.tst` for sample usage.

Lisp-level Functionality

`READLINE:*READLINE-INPUT-STREAM*`
  A `STREAM` (see Section 21.17, “Functions `EXT:MAKE-BUFFERED-INPUT-STREAM` and `EXT:MAKE-BUFFERED-OUTPUT-STREAM` ”) that receives user input using GNU readline and the standard CLISP prompt.

## 33.6. GDBM - The GNU database manager

This is an interface to the GNU DataBase Manager, which extends the standard UNIX <`ndbm.h`>.

When this module is present, `*FEATURES*` contains the symbol `:GDBM`.

See `modules/gdbm/test.tst` for sample usage.

GDBM module API

`(GDBM:GDBM-VERSION)`

  Return the version string.

`(GDBM:GDBM-OPEN `filename` `&KEY` :BLOCKSIZE :READ-WRITE :OPTIONS :MODE :DEFAULT-KEY-TYPE :DEFAULT-VALUE-TYPE)`

  Open `filename` database file. The return value is a GDBM structure. `:READ-WRITE` can have one of following values:

  `:READER`
  `:WRITER`
  `:WRCREAT`
  `:NEWDB`

  `:OPTIONS` is a combination of

  `:FAST`
  `:SYNC`
  `:NOLOCK`
  `:NOMMAP`
  `:CLOEXEC`
  `:BSEXACT`

  `:MODE` is the numeric file permission mode (cf. `open`), use `POSIX:CONVERT-MODE` to extract it from a list of keywords.

  CLISP can store and retrieve values of the following types:

  `STRING`
  `VECTOR` (meaning anything that can be `COERCE`d to `(`VECTOR` (`UNSIGNED-BYTE` 8))`)
  `EXT:32BIT-VECTOR` (meaning `(`VECTOR` `(`UNSIGNED-BYTE` 32)`)`)
  `INTEGER`
  `SINGLE-FLOAT`
  `DOUBLE-FLOAT`

  and `:DEFAULT-KEY-TYPE` and `:DEFAULT-VALUE-TYPE` should be one of those. If not specified (or `NIL`), the `:TYPE` argument is required in the access functions below.

  If `filename` is actually an existing GDBM structure, then it is re-opened (if it has been closed), and returned as is.

  The return value is `EXT:FINALIZE`d with `GDBM-CLOSE`.

`(GDBM:GDBM-PATH `db`)`

  Return the original `filename` passed to .

`(GDBM:GDBM-CLOSE `db`)`
  Close the database.
`(GDBM:GDBM-OPEN-P `db`)`

  Check whether `db` has been already closed.

  ### Warning

  Only the above functions accept closed databases, the following functions `SIGNAL`s an `ERROR` when passed a closed database.

`(GDBM:GDBM-STORE `db` `key` `contents` `&KEY` :FLAG)`

  `db` is the GDBM structure returned by `GDBM:GDBM-OPEN`. `key` is the key datum. `contents` is the data to be associated with the key. `:FLAG` can have one of following values:

  `:INSERT`
  `:REPLACE`

`(GDBM:GDBM-FETCH `db` `key` `&KEY` (TYPE (GDBM:GDBM-OPT `db` :DEFAULT-VALUE-TYPE)))`
  Search the database. The `:TYPE` argument specifies the return type.
`(GDBM:GDBM-DELETE `db` `key`)`
  Delete `key` and its contents.
`(GDBM:GDBM-EXISTS `db` `key`)`
  Search data without retrieving it.
`(GDBM:GDBM-FIRSTKEY `db` `&KEY` (TYPE (GDBM:GDBM-OPT `db` :DEFAULT-KEY-TYPE)))`
  Return the key of the first entry, as `:TYPE`. If the database has no entries, the return value is `NIL`.
`(GDBM:GDBM-NEXTKEY `db` `key` `&KEY` (TYPE (GDBM:GDBM-OPT `db` :DEFAULT-KEY-TYPE)))`
  Return the key that follows `key`, as `:TYPE`, or `NIL` if there are no further entries.
`(GDBM:GDBM-REORGANIZE `db`)`
  Reorganize the database.
`(GDBM:GDBM-SYNC `db`)`
  Syncronize the in-memory state of the database to the disk file.
`(GDBM:GDBM-OPT `db` `option`)`
`(`SETF` (GDBM:GDBM-OPT `db` `option`) `value`)`

  Set or retrieve options of an already open database. `option` is one of following:

  `:FLAGS`
    Retrieve the `:READ-WRITE` and `:OPTIONS` passed to `GDBM:GDBM-OPEN` (read-only).
  `:CACHESIZE`
    Retrieve and set the size of the internal bucket cache.
  `:MAXMAPSIZE`
    Retrieve and set the maximum size of a memory mapped region.
  `:BLOCKSIZE`
    Retrieve the block size in bytes (read-only).
  `:MMAP`
    Retrieve and enable or disable memory mapping mode.
  `:SYNCMODE`
    Retrieve or set file system synchronization mode.
  `:CENTFREE`
    Retrieve or set central free block pool handling.
  `:COALESCEBLKS`
    Retrieve or set free block merging.
  `:DBNAME`
    Retrieve the namestring of the database (read-only).
  `:DEFAULT-VALUE-TYPE`
  `:DEFAULT-KEY-TYPE`
    The default data conversion types, see `GDBM:GDBM-OPEN`.
`(GDBM:GDBM-FILE-SIZE `db`)`
  Return the underlying file size using `lseek`.
`(GDBM:GDBM-COUNT `db`)`
  Return the number of records in the database.
`(GDBM:DO-DB (`key` `db` `&REST` `options`) `&BODY` `body`)`
  Iterate over the database keys, `options` are passed to `GDBM-FIRSTKEY` and `GDBM-NEXTKEY`. `body` is passed to `LOOP`, so you can use all the standard loop contructs, e.g., `(do-db (k db) :collect (list k (gdbm-fetch k)))` will convert the database to an association list.
`(GDBM:WITH-OPEN-DB (`db` `filename` `&REST` `options`) `&BODY` `body`)`
  Open the `filename`, execute the `body`, close the database.

## 33.7. Berkeley DB access

This interface to Berkeley DB from Sleepycat Software/Oracle exports most functions in the official C API. Supported versions:

4.2
4.3
4.4
4.5
4.6
4.7
4.8
5.3

When this module is present, `*FEATURES*` contains the symbol `:BERKELEY-DB`.

See `modules/berkeley-db/test.tst` for sample usage.

### Note

The symbol names do evolve with new Berkeley DB releases. E.g., version 4.3 introduced `DB_DSYNC_LOG` which was renamed to `DB_LOG_DSYNC` in version 4.7. The corresponding Lisp symbol was renamed from `:DSYNC-LOG` to `:LOG-DSYNC` when support for version 4.7 was added. This means that we always use Lisp names which correspond to the C names in the latest Berkeley DB release, even though we keep suport for older releases. This is convenient because the online documentation to which this manual refers documents the latest Berkeley DB release.

### 33.7.1. Berkeley-DB Objects

Thie module exports the following opaque `STRUCTURE-OBJECT` types:

BDB:DBE
  environment handle
BDB:DB
  database handle
BDB:DBC
  cursor handle
BDB:TXN
  transaction handle
BDB:LOGC
  log cursor handle
BDB:MPOOLFILE
  memory pool file handle
BDB:DBLOCK
  lock handle

They contain the internal handle (a `FFI:FOREIGN-POINTER`), the `LIST` of parents, and the `LIST` of dependents.

### 33.7.2. Closing handles

`CLOSE` will close (or commit, in the case of a transaction, or put, in the case of a lock) the Berkeley-DB handle objects. The garbage-collector will also call `CLOSE`. Closing an object will `CLOSE` all its dependents and remove the object itself from the dependents lists of its parents (but see `BDB:LOCK-CLOSE`).

### 33.7.3. Database Environment

`(BDB:DB-VERSION `&OPTIONAL` subsystems-too)`

  Return version information as multiple values:

  1. descriptive `STRING` (from `db_version`)
  2. major version number (`FIXNUM`)
  3. minor version number (`FIXNUM`)
  4. patch number (`FIXNUM`)

  When the optional argument is non-`NIL`, returns the association list of the subsystem versions as the 5th value.

`(BDB:DBE-CREATE `&KEY` PASSWORD ENCRYPT)`
  Create an environment handle (`db_env_create`), possibly using encryption with password (`DB_ENV->set_encrypt`).
`(BDB:DBE-CLOSE dbe)`
  Close an environment (`DB_ENV->close`). You can also call `CLOSE`.
`(BDB:DBE-MESSAGES dbe)`
  Return the verbose messages accumulated so far (requires Berkeley-DB 4.3 or better).
`(BDB:DBREMOVE dbe file database `&KEY` TRANSACTION AUTO-COMMIT)`
  Remove a database (`DB_ENV->dbremove`).
`(BDB:DBREMOVE dbe file database newname `&KEY` TRANSACTION AUTO-COMMIT)`
  Rename a database (`DB_ENV->dbrename`).
`(BDB:DBE-OPEN dbe `&KEY` FLAGS HOME JOIN INIT-CDB INIT-LOCK INIT-LOG INIT-MPOOL INIT-TXN RECOVER RECOVER-FATAL USE-ENVIRON USE-ENVIRON-ROOT CREATE LOCKDOWN PRIVATE SYSTEM-MEM THREAD MODE)`
  Open an environment (`DB_ENV->open`). `:FLAGS` may be the value of a previous call to `(`BDB:DBE-GET-OPTIONS` dbe :OPEN)`.
`(BDB:DBE-REMOVE dbe `&KEY` HOME FORCE USE-ENVIRON USE-ENVIRON-ROOT)`
  Destroy an environment (`DB_ENV->remove`).
`(BDB:WITH-DBE (var `&KEY` `create` `options`) `&BODY` body)`
  Create an environment, execute `body`, close it. `create` is a list of options to be passed to `BDB:DBE-CREATE`, `options` is a list of options to be passed to `BDB:DBE-SET-OPTIONS`.

### 33.7.4. Environment Configuration

`(BDB:DBE-SET-OPTIONS dbe `&KEY` MSGFILE ERRFILE ERRPFX PASSWORD ENCRYPT LOCK-TIMEOUT TXN-TIMEOUT SHM-KEY TAS-SPINS TX-TIMESTAMP TX-MAX DATA-DIR TMP-DIR INTERMEDIATE-DIR-MODE LG-BSIZE LG-DIR LG-MAX LG-REGIONMAX NCACHE CACHESIZE CACHE LK-CONFLICTS LK-DETECT LK-MAX-LOCKERS LK-MAX-LOCKS LK-MAX-OBJECTS LOG-DIRECT LOG-DSYNC LOG-AUTO-REMOVE LOG-IN-MEMORY LOG-ZERO AUTO-COMMIT CDB-ALLDB DIRECT-DB NOLOCKING NOMMAP NOPANIC OVERWRITE PANIC-ENVIRONMENT REGION-INIT TXN-NOSYNC TXN-WRITE-NOSYNC YIELDCPU VERB-CHKPOINT VERB-DEADLOCK VERB-RECOVERY VERB-REPLICATION VERB-WAITSFOR VERBOSE)`

  Set some environment options using

  `DB_ENV->set_flags` | `DB_ENV->set_shm_key` | `DB_ENV->set_lg_regionmax`
  `DB_ENV->log_set_config` (v4.7+) | `DB_ENV->set_timeout` | `DB_ENV->set_lk_conflicts`
  `DB_ENV->set_verbose` | `DB_ENV->set_encrypt` | `DB_ENV->set_lk_detect`
  `DB_ENV->set_intermediate_dir_mode` (v4.7+) | `DB_ENV->set_errfile` | `DB_ENV->set_lk_max_lockers`
  `DB_ENV->set_tmp_dir` | `DB_ENV->set_msgfile` | `DB_ENV->set_lk_max_locks`
  `DB_ENV->set_data_dir` | `DB_ENV->set_errpfx` | `DB_ENV->set_lk_max_objects`
  `DB_ENV->set_tx_max` | `DB_ENV->set_lg_bsize` | `DB_ENV->set_cachesize`
  `DB_ENV->set_tx_timestamp` | `DB_ENV->set_lg_dir` |
  `DB_ENV->set_tas_spins` | `DB_ENV->set_lg_max` |

`(BDB:DBE-GET-OPTIONS dbe `&OPTIONAL` `what`)`

  Retrieve some environment options.

  Values of `what`

  missing
  `NIL`
    all options as a `LIST`
  `:TX-TIMESTAMP`
    Recover to the time specified by timestamp rather than to the most current possible date (`DB_ENV->get_tx_timestamp`)
  `:TX-MAX`
    the number of active transactions (`DB_ENV->set_tx_max`)
  `:DATA-DIR`
    list of data directories (`DB_ENV->get_data_dir`)
  `:TMP-DIR`
    temporary directory (`DB_ENV->get_tmp_dir`). May be `NIL`.
  `:INTERMEDIATE-DIR-MODE`
    mode for creating intermediate directories during recovery (v4.7+) (`DB_ENV->get_intermediate_dir_mode`).
  `:VERBOSE`
    the `LIST` of verbosity settings (`DB_ENV->get_verbose`).
  `:AUTO-COMMIT`
  `:CDB-ALLDB`
  `:DIRECT-DB`
  `:LOG-DIRECT`
  `:LOG-DSYNC`
  `:LOG-AUTO-REMOVE`
  `:LOG-IN-MEMORY`
  `:LOG-ZERO`
  `:NOLOCKING`
  `:NOMMAP`
  `:NOPANIC`
  `:OVERWRITE`
  `:PANIC-ENVIRONMENT`
  `:REGION-INIT`
  `:TXN-NOSYNC`
  `:TXN-WRITE-NOSYNC`
  `:YIELDCPU`
  `:VERB-CHKPOINT`
  `:VERB-DEADLOCK`
  `:VERB-RECOVERY`
  `:VERB-REPLICATION`
  `:VERB-WAITSFOR`
    a `BOOLEAN` indicator of whether this option is set or not (`DB_ENV->get_verbose`, `DB_ENV->get_flags`, and `DB_ENV->log_get_config`).
  `:LG-BSIZE`
    log buffer size (`DB_ENV->get_lg_bsize`).
  `:LG-DIR`
    logging directory (`DB_ENV->get_lg_dir`).
  `:LG-MAX`
    log file size (`DB_ENV->get_lg_max`).
  `:LG-REGIONMAX`
    logging region size (`DB_ENV->get_lg_regionmax`).
  `:NCACHE`
  `:CACHESIZE`
  `:CACHE`
    cache parameters (`DB_ENV->get_cachesize`).
  `:LK-CONFLICTS`
    lock conflicts matrix (`DB_ENV->get_lk_conflicts`).
  `:LK-DETECT`
    automatic deadlock detection (`DB_ENV->get_lk_detect`).
  `:LK-MAX-LOCKERS`
    maximum number of lockers (`DB_ENV->get_lk_max_lockers`).
  `:LK-MAX-LOCKS`
    maximum number of locks (`DB_ENV->get_lk_max_locks`).
  `:LK-MAX-OBJECTS`
    maximum number of lock objects (`DB_ENV->get_lk_max_objects`).
  `:TAS-SPINS`
    the number of test-and-set spins (`DB_ENV->get_tas_spins`).
  `:SHM-KEY`
    base segment ID for shared memory regions (`DB_ENV->get_shm_key`).
  `:LOCK-TIMEOUT`
  `:TXN-TIMEOUT`
    timeout values for locks or transactions in the database environment (`DB_ENV->get_timeout`).
  `:ENCRYPT`
    encryption flags (`DB_ENV->get_encrypt_flags`).
  `:ERRFILE`
    file descriptor or `NIL` (`DB_ENV->get_errfile`).
  `:MSGFILE`
    file descriptor or `NIL` (`DB_ENV->get_msgfile`).
  `:ERRPFX`
    `STRING` or `NIL` (`DB_ENV->get_errpfx`).
  `:DB-GID-SIZE`
    the `LENGTH` of the globally unique `(`VECTOR` (`UNSIGNED-BYTE` 8))` which must be passed to `DB_TXN->prepare`.
  `:HOME`
    the home directory when open (`DB_ENV->get_home`).
  `:OPEN`
    the `LIST` of flags passed to `BDB:DBE-OPEN` (`DB_ENV->get_open_flags`).
  `:CACHE`
    database cache information (`DB_ENV->get_cachesize`).

### 33.7.5. Database Operations

`(BDB:DB-CREATE dbe)`
  Create a database handle (`db_create`).
`(BDB:DB-CLOSE db `&KEY` NOSYNC)`
  Close a database (`DB->close`). You can also call `CLOSE`.
`(BDB:DB-DEL dbe key `&KEY` TRANSACTION AUTO-COMMIT)`
  Delete items from a database (`DB->del`).
`(BDB:DB-FD db)`
  Return the file descriptor for the database (`DB->fd`).
`(BDB:DB-GET db key `&KEY` ACTION AUTO-COMMIT DEGREE-2 DIRTY-READ MULTIPLE RMW TRANSACTION (ERROR `T`))`

  Get items from a database (`DB->get`). If `:ERROR` is `NIL` and the record is not found, no `ERROR` is `SIGNAL`ed, instead `:NOTFOUND` is returned. `:ACTION` should be one of

  `:CONSUME` | `:GET-BOTH`
  `:CONSUME-WAIT` | `:SET-RECNO`

`(BDB:DB-PUT db key val `&KEY` AUTO-COMMIT ACTION TRANSACTION)`

  Store items into a database (`DB->put`). `:ACTION` should be one of

  `:APPEND` | `:NODUPDATA` | `:NOOVERWRITE`

`(BDB:DB-STAT db `&KEY` FAST-STAT TRANSACTION)`
  Return database statistics (`DB->get_byteswapped`, `DB->get_type`, `DB->stat`).
`(BDB:DB-OPEN db file `&KEY` DATABASE TYPE MODE FLAGS CREATE DIRTY-READ EXCL NOMMAP RDONLY THREAD TRUNCATE AUTO-COMMIT TRANSACTION)`

  Open a database (`DB->open`). `:TYPE` should be one of

  `:BTREE` | `:RECNO`
  `:HASH` | `:UNKNOWN` (default)
  `:QUEUE` |

  `:FLAGS` may be the value of a previous call to `(`BDB:DB-GET-OPTIONS` db :OPEN)`

`(BDB:DB-SYNC db)`
  Flush a database to stable storage (`DB->sync`).
`(BDB:DB-TRUNCATE db `&KEY` TRANSACTION AUTO-COMMIT)`
  Empty a database (`DB->truncate`).
`(BDB:DB-UPGRADE db file `&KEY` DUPSORT)`
  Upgrade a database (`DB->upgrade`).
`(BDB:DB-RENAME db file database newname)`
  Rename a database (`DB->rename`).
`(BDB:DB-REMOVE db file database)`
  Remove a database (`DB->remove`).
`(BDB:DB-JOIN db cursor-sequence `&KEY` JOIN-NOSORT)`
  Create a specialized join cursor for use in performing equality or natural joins on secondary indices (`DB->join`).
`(BDB:DB-KEY-RANGE db key `&KEY` TRANSACTION)`
  return an estimate of the proportion of keys that are less than, equal to, and greater than the specified key (`DB->key_range`). The underlying database must be of type Btree.
`(BDB:DB-VERIFY db file `&KEY` DATABASE SALVAGE AGGRESSIVE PRINTABLE NOORDERCHK)`
  Verify/salvage a database (`DB->verify`). `:SALVAGE`, if supplied, should be the output file name. `:DATABASE`, if supplied, will force `DB_ORDERCHKONLY`.
`(BDB:WITH-DB (var dbe file `&KEY` `create` `options` `open`) `&BODY` body)`
  Open the database, execute `body`, close it. `create` is a list of options to be passed to `BDB:DB-CREATE`, `options` is a list of options to be passed to `BDB:DB-SET-OPTIONS`, `open` is a list of options to be passed to `BDB:DB-OPEN`.
`(BDB:DB-COMPACT db `&KEY` TRANSACTION START STOP FREE FILL TIMEOUT PAGES TYPE)`
  Call `DB->compact`. `:FREE` is either `:LIST-ONLY` or `:SPACE`. `:FILL`, `:TIMEOUT`, `:PAGES` are passed in DB_COMPACT. `:TYPE` is how the `end` is returned. The second return value is a BDB:DB-COMPACT.

### 33.7.6. Database Configuration

`(BDB:DB-SET-OPTIONS db `&KEY` ERRFILE MSGFILE ERRPFX PASSWORD ENCRYPTION NCACHE CACHESIZE CACHE LORDER PAGESIZE BT-MINKEY H-FFACTOR H-NELEM Q-EXTENTSIZE RE-DELIM RE-LEN RE-PAD RE-SOURCE CHKSUM ENCRYPT TXN-NOT-DURABLE DUP DUPSORT INORDER RECNUM REVSPLITOFF RENUMBER SNAPSHOT)`

  Set some database options using

  `DB_ENV->set_errfile` | `DB->set_pagesize` | `DB->set_re_len`
  `DB_ENV->set_msgfile` | `DB->set_bt_minkey` | `DB->set_re_pad`
  `DB_ENV->set_errpfx` | `DB->set_h_ffactor` | `DB->set_re_source`
  `DB->set_encrypt` | `DB->set_h_nelem` | `DB->set_flags`
  `DB->set_cachesize` | `DB->set_q_extentsize` |
  `DB->set_lorder` | `DB->set_re_delim` |

`(BDB:DB-GET-OPTIONS db `&OPTIONAL` `what`)`

  Retrieve some database options.

  Values of `what`

  missing
  `NIL`
    all options as a `LIST`
  `:FLAGS`
    all flags (`DB_ENV->get_flags`).
  `:CHKSUM`
  `:ENCRYPT`
  `:TXN-NOT-DURABLE`
  `:DUP`
  `:DUPSORT`
  `:INORDER`
  `:RECNUM`
  `:REVSPLITOFF`
  `:RENUMBER`
  `:SNAPSHOT`
    a `BOOLEAN` indicator of whether this option is set or not (`DB_ENV->get_verbose` and `DB_ENV->get_flags`).
  `:CACHE`
    database cache information (`DB->get_cachesize` or `DB_ENV->get_cachesize` if the database was created within an environment).
  `:ENCRYPTION`
    encryption flags (`DB_ENV->get_encrypt_flags`).
  `:ERRFILE`
    file descriptor or `NIL` (`DB_ENV->get_errfile`).
  `:MSGFILE`
    file descriptor or `NIL` (`DB_ENV->get_msgfile`).
  `:ERRPFX`
    `STRING` or `NIL` (`DB_ENV->get_errpfx`).
  `:PAGESIZE`
    database page size (`DB->get_pagesize`).
  `:BT-MINKEY`
    the minimum number of key/data pairs intended to be stored on any single `:BTREE` leaf page underlying source file (`DB->get_bt_minkey`).
  `:H-FFACTOR`
    the desired density within the `:HASH` table (`DB->get_h_ffactor`).
  `:H-NELEM`
    an estimate of the final size of the `:HASH` table (`DB->get_h_nelem`).
  `:Q-EXTENTSIZE`
    the size of the extents used to hold pages in a `:QUEUE` database (`DB->get_q_extentsize`).
  `:RE-DELIM`
    the record delimiter for `:RECNO` databases (`DB->get_re_delim`).
  `:RE-LEN`
    database record length (`DB->get_re_len`).
  `:RE-PAD`
    database record pad byte (`DB->get_re_pad`).
  `:RE-SOURCE`
    the underlying source file for `:RECNO` databases (`DB->get_re_source`).
  `:LORDER`
    database byte order (`DB->get_lorder`).
  `:DBNAME`
    the file name and database name (`DB->get_dbname`)
  `:TRANSACTIONAL`
    the indicator whether the database is transactional (`DB->get_transactional`).
  `:OPEN`
    the flags passed to `BDB:DB-OPEN` (`DB->get_open_flags`).

  ### Warning

  Once you call a method for one type of access method, the handle can only be used for that type. The methods `DB->get_re_delim` and `DB->get_re_source` are for a `:RECNO` database so you cannot call them (by passing `:RE-DELIM` or `:RE-SOURCE` to this function) and then use the database handle to open a database of different type (e.g., `:QUEUE`).

### 33.7.7. Database Cursor Operations

`(BDB:MAKE-DBC db `&KEY` DEGREE-2 DIRTY-READ WRITECURSOR TRANSACTION)`
  Create a cursor handle (`DB->cursor`).
`(BDB:DBC-CLOSE cursor)`
  Close the cursor handle (`DBCursor->close`). You can also call `CLOSE`.
`(BDB:DBC-COUNT cursor)`
  Return count of duplicates (`DBCursor->count`).
`(BDB:DBC-DEL cursor `&KEY` CONSUME)`
  Delete by cursor (`DBCursor->del`).
`(BDB:DBC-DUP cursor `&KEY` POSITION)`
  Duplicate a cursor (`DBCursor->dup`).
`(BDB:DBC-GET cursor key data action `&KEY` DEGREE-2 DIRTY-READ MULTIPLE (ERROR `T`))`

  Retrieve by cursor (`DBCursor->get`). If `:ERROR` is `NIL` and the record is not found, no `ERROR` is `SIGNAL`ed, `:NOTFOUND` or `:KEYEMPTY` is returned instead, as appropriate. `action` should be one of

  `:CURRENT` | `:GET-RECNO` | `:NEXT-DUP` | `:SET`
  `:FIRST` | `:JOIN-ITEM` | `:NEXT-NODUP` | `:SET-RANGE`
  `:GET-BOTH` | `:LAST` | `:PREV` | `:SET-RECNO`
  `:GET-BOTH-RANGE` | `:NEXT` | `:PREV-NODUP` |

`(BDB:DBC-PUT cursor key data flag)`
  Store by cursor (`DBCursor->put`).
`(BDB:WITH-DBC (var `&REST` `options`) `&BODY` `body`))`
  Open a cursor, execute `body`, close it. `options` are passed to `BDB:MAKE-DBC`.

### 33.7.8. Lock Subsystem

`(BDB:LOCK-DETECT dbe action)`
  Perform deadlock detection (`DB_ENV->lock_detect`).
`(BDB:LOCK-ID dbe)`
  Acquire a locker ID (`DB_ENV->lock_id`).
`(BDB:LOCK-ID-FREE dbe id)`
  Release a locker ID (`DB_ENV->lock_id_free`). All associated locks should be released first.
`(BDB:LOCK-GET dbe object locker mode `&KEY` NOWAIT)`
  Acquire a lock (`DB_ENV->lock_get`). The BDB:DBLOCK object returned by this function will not be released when the environment is closed. This permits long-lived locks.
`(BDB:LOCK-PUT dbe lock)`
  Release a lock (`DB_ENV->lock_put`).
`(BDB:LOCK-CLOSE lock)`

  Release a lock (`DB_ENV->lock_put`) using the environment with which it has been acquired. This is used to `EXT:FINALIZE` BDB:DBLOCK objects.

  ### Warning

  If that environment has already been closed, you are in a big trouble (segfault), so you better release your locks or do not drop them.

`(BDB:LOCK-STAT dbe `&KEY` STAT-CLEAR)`
  Return lock subsystem statistics (`DB_ENV->lock_stat`).

### 33.7.9. Log Subsystem

`(BDB:LOG-ARCHIVE dbe `&KEY` ARCH-ABS ARCH-DATA ARCH-LOG ARCH-REMOVE)`
  Return a list of log or database filenames (`DB_ENV->log_archive`).
`(BDB:LOG-FILE dbe lsn)`
  Return the name of the file containing the record named by `lsn` (`DB_ENV->log_file`).
`(BDB:LOG-FLUSH dbe lsn)`
  Flush log records to disk (`DB_ENV->log_flush`).
`(BDB:LOG-PUT dbe data `&KEY` :FLUSH)`
  Write a log record (`DB_ENV->log_put`).
`(BDB:LOG-STAT dbe `&KEY` STAT-CLEAR)`
  Logging subsystem statistics (`DB_ENV->log_stat`).

#### 33.7.9.1. Log Cursor Operations

`(BDB:LOG-CURSOR dbe)`
  Create a log cursor handle (`DB_ENV->log_cursor`).
`(BDB:LOGC-CLOSE logc)`
  Close a log cursor handle (`DB_LOGC->close`).
`(BDB:LOGC-GET logc action `&KEY` TYPE ERROR)`

  Retrieve a log record (`DB_LOGC->get`). If `:ERROR` is `NIL` and the record is not found, no `ERROR` is `SIGNAL`ed, `:NOTFOUND` is returned instead.

  Valid `action`s

  `:CURRENT`
  `:FIRST`
  `:LAST`
  `:NEXT`
  `:PREV`
    Retrieve the appropriate record.
  DB:LSN
    Retrieve the specified record, as with `DB_SET`.

  Returns two values: the datum of type specified by the `:TYPE` argument and the DB:LSN value of the record retrieved (when `action` is a DB:LSN, it is returned unchanged).

#### 33.7.9.2. Log Sequence Numbers

Use `EQUALP` to check similarity of BDB:LSN objects.

`(BDB:LOG-COMPARE lsn1 lsn2)`
  Compare two Log Sequence Numbers (`log_compare`).

### 33.7.10. Memory Pool Subsystem

not implemented yet, patches are welcome

### 33.7.11. Replication

not implemented yet, patches are welcome

### 33.7.12. Sequences

not implemented yet, patches are welcome

### 33.7.13. Transaction Subsystem

`(BDB:TXN-BEGIN dbe `&KEY` DEGREE-2 PARENT DIRTY-READ NOSYNC NOWAIT SYNC)`
  Begin a transaction (`DB_ENV->txn_begin`).
`(BDB:TXN-ABORT txn)`
  Abort a transaction (`DB_TXN->abort`).
`(BDB:TXN-COMMIT txn `&KEY` NOSYNC SYNC)`
  Commit a transaction (`DB_TXN->commit`).
`(BDB:TXN-DISCARD txn)`
  Discard a transaction (`DB_TXN->discard`).
`(BDB:TXN-ID txn)`
  Return the transaction's ID (`DB_TXN->id`).
`(BDB:TXN-CHECKPOINT dbe `&KEY` KBYTE MIN FORCE)`
  Checkpoint the transaction subsystem (`DB_ENV->txn_checkpoint`).
`(BDB:TXN-PREPARE txn id)`
  Initiate the beginning of a two-phase commit (`DB_TXN->prepare`).
`(BDB:TXN-RECOVER dbe `&KEY` FIRST NEXT)`
  Return a list of prepared but not yet resolved transactions (`DB_ENV->txn_recover`).
`(BDB:TXN-SET-TIMEOUT txn timeout which)`
  Set timeout values for locks or transactions for the specified transaction (`DB_TXN->set_timeout`).
`(BDB:TXN-STAT dbe `&KEY` STAT-CLEAR)`
  Transaction subsystem statistics (`DB_ENV->txn_stat`).

## 33.8. Directory Access

This module provides some directory access from lisp, in package “LDAP”.

When this module is present, `*FEATURES*` contains the symbol `:DIRKEY`.

3 types of directory keys may exist, depending on the compilation environment.

valid directory key types

:win32
  Win32 registry access
:gnome
  gnome-config access
:ldap
  LDAP interface via OpenLDAP or compatible

The following functions and macros are exported (please note that these features are experimental and the API may be modified in the future).

`(`LDAP:DIR-KEY-OPEN` `dkey` `pathname` `&KEY` (`:DIRECTION` `:INPUT`) `:IF-DOES-NOT-EXIST`)`
  Open the directory key under `dkey`, which should be either an open directory key or a valid directory key type. The meaning of the `:DIRECTION` and `:IF-DOES-NOT-EXIST` keyword arguments is the same as for `OPEN`.
`(`LDAP:DIR-KEY-CLOSE` `dkey`)`
  Close the directory key. The preferred way is to use the `LDAP:WITH-DIR-KEY-OPEN` macro.
`(`LDAP:WITH-DIR-KEY-OPEN` (`variable` `dkey` `pathname` `&REST` {`option`}*) `&BODY` `body`)`
  Open the directory key (by calling `LDAP:DIR-KEY-OPEN` on `dkey`, `pathname` and `option`s), bind it to `variable`, execute `body`, then close it with `LDAP:DIR-KEY-CLOSE`.
`(`LDAP:DIR-KEY-TYPE` `dkey`)`
  Return the directory key type of the directory key
`(`LDAP:DIR-KEY-PATH` `dkey`)`
  Return the path of this directory key, which is the `pathname` argument of `LDAP:DIR-KEY-OPEN` if `dkey` was a directory key type or the concatenation of the `pathname` argument and the `ldap:dir-key-path` of `dkey`.
`(`LDAP:DIR-KEY-DIRECTION` `dkey`)`
  One of `:INPUT`, `:OUTPUT` and `:IO`, indicating the permitted operation on this key and its derivatives.
`(`LDAP:DIR-KEY-CLOSED-P` `dkey`)`
  Check whether the key has been closed. It is not an error to close a closed key.
`(`LDAP:DIR-KEY-SUBKEY-DELETE` `dkey` `subkey`)` `(`LDAP:DIR-KEY-VALUE-DELETE` `dkey` `attribute`)`
  Delete the specified subkey or attribute.
`(`LDAP:DIR-KEY-SUBKEY` `dkey`)` `(`LDAP:DIR-KEY-ATTRIBUTES` `dkey`)`
  Return the list of the subkeys or attributes.
`(`LDAP:DIR-KEY-VALUE` `dkey` `attribute` `&OPTIONAL` `default`)`
  Return the value of the specified attribute, similar to `GETHASH` and `SETF`able just like `GETHASH`.
`(`LDAP:DIR-KEY-INFO` `dkey`)`
  Return some information about the directory key. This is highly platform-dependent and will probably be removed or replaced or modified in the future.
`(`LDAP:WITH-DIR-KEY-SEARCH` (`key-iter` `atribute-iter` `dkey` `pathname` `&KEY` `:scope`) `&BODY` `body`)`

  This is the main way to iterate over the subtree under the key `dkey`+`pathname`.

  `key-iter` is a non-`NIL` symbol and is bound via `MACROLET` to a macro, each call of which returns the next subkey.

  `atribute-iter` is a symbol and is bound, when non-`NIL`, to a macro, each call of which returns two values - the next attribute and its value.

  The `:scope` keyword argument specifies the scope of the search and can be

  `:self`
    iterate over the key itself
  `:level`
    iterate over the children of the key
  `:tree`
    iterate over the subtree

  `LDAP:WITH-DIR-KEY-SEARCH` is used to implement `LDAP:DIR-KEY-VALUES`, `LDAP:DIR-KEY-CHILDREN` and `LDAP:DIR-KEY-DUMP-TREE` in `modules/dirkey/dirkey1.lisp`.

## 33.9. PostgreSQL Database Access

This package offers an “FFI”-based interface to PostgreSQL.

The package “SQL” (nicknamed “POSTGRES” and “POSTGRESQL”) is `:CASE-SENSITIVE`, so you would write `(sql:PQconnectdb ...)` when you need to call `PQconnectdb`.

When this module is present, `*FEATURES*` contains the symbol `:POSTGRESQL`.

See `modules/postgresql/test.tst` for sample usage.

Additionally, some higher level functionality is available (defined in `modules/postgresql/sql.lisp`):

`(sql:pq-finish `connection`)`
  `PQfinish` the `connection` and mark it as invalid
`(sql:pq-clear `result`)`
  `PQclear` the `result` and mark it as invalid
`(sql:sql-error `connection` `result` `format-string` `&REST` `arguments`)`
  finalize `connection` and `result` and `SIGNAL` an appropriate `ERROR`
`(sql:sql-connect `&KEY` host port options tty name login password)`
  call `PQsetdbLogin` and return the `connection`
`(sql:with-sql-connection (`variable` `&REST` `option`s `&KEY` `log` `&ALLOW-OTHER-KEYS`) `&BODY` `body`)`

  1. bind `*sql-log*` to the `log` argument

  2. call `sql:sql-connect` on `option`s and bind `variable` to the result

  3. execute `body`

  4. call `sql:pq-finish` on `variable`

`(sql:sql-transaction `connection` `command` `status` `&OPTIONAL` (clear-p `T`))`
  execute the `command` via `connection`; if the status does not match `status`, `ERROR` is `SIGNAL`ed; if `clear-p` is non-`NIL` `sql:pq-clear` the `result`; otherwise return it
`(sql:with-sql-transaction (`result` `connection` `command` status) `&BODY` `body`)`
  execure the `body` on the `result` of `command`, then `sql:pq-clear` the `result`
`sql:*sql-login*`
  the default `login` argument to `sql:sql-connect` (initially set to `"postgres"`)
`sql:*sql-password*`
  the default `password` argument to `sql:sql-connect` (initially set to `"postgres"`)
`sql:*sql-log*`
  when non-`NIL`, should be a `STREAM`; `sql:sql-connect` and `sql:sql-transaction` will write to it (initially set to `NIL`)

### Warning

Since `PQfinish` and `PQclear` cannot be called on the same pointer twice, one needs to track their validity (`sql:sql-connect` and `sql:sql-transaction` take care of that). See Example 32.11, “Controlling validity of resources”.

For `PQtrace`, see Section 33.2.14, “Standard file input and output”.

## 33.10. Oracle Interface

The Oracle module allows a CLISP program to act as client to an Oracle database server. The module includes full SQL support, transactions (including auto-commit), support for most Oracle data types (LONG, BLOB, CLOB, RAW, etc.), automatic conversion between Oracle and Common Lisp data types, database connection caching and retry, concurrent connections to multiple databases, proper handling of Oracle errors, and more.

The module can be used to build sophisticated Oracle database applications in Common Lisp.

When this module is present, `*FEATURES*` contains the symbol `:ORACLE`.

### 33.10.1. Functions and Macros in package “ORACLE”

Access to Oracle is via these functions and macros in package “ORACLE”. When any Oracle function fails, the general Lisp function `ERROR` is called, with the condition string set to include the Oracle error number, the Oracle message text, and other context of the error (e.g., the text and parse location of a SQL query).

`(ORACLE:CONNECT `user` `password` `server` `&OPTIONAL` `schema` `auto-commit` `prefetch-buffer-bytes` `long-len` `truncate-ok`)`

  Connect to an Oracle database. All subsequent operations will affect this database until the next call to `ORACLE:CONNECT`. A single program can access different Oracle schemas concurrently by repeated calls to `ORACLE:CONNECT`. Database connections are cached and re-used: if you call `ORACLE:CONNECT` again with the same `user`, `schema`, and `server`, the previous Oracle connection will be re-used. `ORACLE:CONNECT` may not be called inside `WITH-TRANSACTION`. Returns: `T` if a cached connection was re-used, `NIL` if a new connection was created (and cached). The meaning of the arguments is as follows:

  Arguments for `ORACLE:CONNECT`

  `user`
    Oracle user ID
  `password`
    Password for user, or `NIL` if `user` has no password (!).
  `server`
    Oracle server ID (SID).
  `schema`
    Oracle default schema (default: `NIL`). If `NIL`, same as user. This allows you to log on with one user's id/password but see the database as if you were some other user.
  `auto-commit`
    Flag: whether to commit after every operation (default: `T`). Set this to `NIL` if you intend to do transactions and call `COMMIT` explicitly. However, `WITH-TRANSACTION` is probably easier.
  `prefetch-buffer-bytes`
    Number of bytes to cache from SQL SELECT fetches (default: 64 Kbytes) If you are very short of memory, or have a slow connection to Oracle, you can reduce this to 10k or so. Alternatively, if you have a fast connection to Oracle and regularly do large queries, you can increase throughput by increasing this value.
  `long-len`
    Number of bytes to fetch for "long" (LONG, [BC]LOB) types. Long data that exceeds this size will raise an error, or be truncated depending on the value of `truncate-ok` (below). Setting `long-len` to zero and `truncate-ok` to `NIL` will disable long fetching entirely. If `long-len` is `NIL` or negative, defaults to 500k bytes.
  `truncate-ok`
    Flag: if set, allow truncation of LONG columns to `long-len` bytes on fetch; otherwise, fetches of LONG columns exceeding `long-len` bytes will raise an error. Default: `NIL`.
`(ORACLE:DISCONNECT)`
  Disconnect from the database currently connected. No more calls can be made until `ORACLE:CONNECT` is called again. The connection is closed and removed from the connection cache. Does nothing if there is no connection. `DISCONNECT` may not be called inside `WITH-TRANSACTION`. Returns `NIL`.
`(ORACLE:RUN-SQL `sql` `&OPTIONAL` `params` `is-select`)`

  Execute a SQL statement. Must be `ORACLE:CONNECT`ed to a database. Returns the number of rows affected by the SQL operation, for non-SELECT statements, zero for SELECT statements. For destructive database operations (INSERT, UPDATE, DELETE), the results are committed to the database immediately if `auto-commit` when establishing the current connection; see `ORACLE:CONNECT`. The meaning of the arguments is as follows:

  Arguments for `RUN-SQL`

  `sql`
    Text of SQL statement, as a string. The `sql` statement may contain Oracle "named parameters," e.g. ":myparam" whose values will be substituted from the parameters given in `params`.
  `params`
    A mapping of the names of the bind-parameters in the query to their values. The set of named parameters in the query must match exactly the keys mapped by `params`. The mapping may be passed as either (1) a hash table whose keys are the named parameters or (2) a list of pairs, ((name value) (name value) ...). Parameter values passed from Lisp are converted to the appropriate Oracle data types (see `FETCH`).
  `is-select`
    Flag: whether the statement is a SELECT query. You usually do not need to set this as it is detected by default based on the SQL text. However, there are situations, such as when a SELECT query begins with comment, that you need to specify it explicitly.
`(ORACLE:DO-ROWS `vars` `&BODY` `body`)`

  Macro which loops over a SQL SELECT result, evaluating, for each row in the result, the forms in `body`, binding symbols given in `vars` to corresponding database columns in the SELECT result. The argument `vars` must be a non-empty list of symbols matching a subset of the columns of an active SELECT query. If a SELECT column is an Oracle expression such as `SUBSTR(mycol, 1, 10)`, it is recommended to use a column alias, e.g., `SELECT SUBSTR(mycol, 1, 10) AS myvar`, in which case the column alias will be used as the symbol bound to the column value.

  As `DO-ROWS` expands into a `DO*` loop, it may be terminated prematurely, before all rows are fetched, by using `RETURN` anywhere in `body`.

  It is allowed to call `ORACLE:CONNECT` in the `body` of the loop, but only to switch the connection to a database other than the one that was used to do the SELECT. This is useful for reading from one database while writing to another.

  In `vars`, instead of a single symbol, a pair (`bound-var` `"column-name"`) may be specified, which will cause values from the SELECTed column or alias , `column-name`, to be bound to Lisp variable, `bound-var`. This is for unusual cases where a Lisp variable cannot be created with the same name as the column (e.g., a column named "T"), or when it is inconvenient or impossible to alias the column with `SELECT ... AS`.

`(ORACLE:FETCH `&OPTIONAL` `result-type`)`

  Fetch a single row of data. Returns a row of values corresponding to the columns of an active SELECT statment. The row data is returned in one of three different forms, depending on the value of the symbol `result-type`:

  Return values for `FETCH`

  `ARRAY`
    Values will be returned in an `ARRAY` with the same number of columns as in the SELECT statement, in the same order. This is the default.
  `PAIRS`
    A list of pairs, `((column, value) ...)` is be returned. The number and order of pairs is the same as the columns in the SELECT statement.
  `HASH`
    A `HASH-TABLE` whose keys are the column names and whose values are the column values in the row. The SELECT columns must be unique and be valid Lisp symbols to use this option. If you are SELECTing an expression, you probably want to use a column alias: `SELECT <expr> AS some_alias ...`

  The following data type conversions are done between Oracle datatypes and Common Lisp data types:

  Oracle type | Converts to/from Common Lisp type
  --- | ---
  Numeric (NUMBER, INTEGER, FLOAT) | The appropriate Common Lisp numeric type (`FIXNUM`, `BIGNUM`, `FLOAT`)
  String (CHAR, VARCHAR, VARCHAR2) | A Common Lisp `STRING`. Note that CHAR will be padded out to its full, fixed length as defined in Oracle; VARCHAR will be a string of variable length. Also note that Oracle has no "zero-length string" value - it returns the SQL special value `NULL` which is converted to `NIL` (see below).
  DATE | A string of the form "YYYY-MM-DD HH:MM:SS" where HH is 24-hour form. If you want dates formatted differently, convert them to strings in Oracle using `SELECT TO_CHAR(mydate, '`template`') AS mydate`; the result will then be returned as a string, formatted as per `template`.
  RAW, LONG RAW | A hexadecimal string, with two hex digits for each byte of Oracle data. Note that this means the Lisp string will be twice the size, in bytes, as the Oracle data.
  "Large" types (LONG, BLOB, CLOB) | A Lisp string of (arbitrary, possibly binary) data. Note that truncation may occur; see the `ORACLE:CONNECT` parameters `long-len` and `truncate-ok`.
  `NULL` | The Common Lisp value `NIL`

`(ORACLE:FETCH-ALL `&OPTIONAL` `max-rows` `result-type` `item-type`)`

  Fetch some or all the rows from a query and return result as a sequence of sequences. Arguments are all optional: `max-rows` limits the result to that numbers of rows; `result-type` is the type of sequence of the rows, either '`ARRAY` (the default) or '`LIST`; `item-type` is the type of sequence of the column values for each row, either '`ARRAY` (the default) or '`LIST`. Each row fetched always contains the full set of column values SELECTed.

  `FETCH-ALL` is often useful in conjunction with `MAP` or `REDUCE` to iterate over an entire SELECT result to construct a single Lisp value.

`(ORACLE:PEEK `&OPTIONAL` `result-type`)`
  Peek at next row of data (without fetching it). Returns a row a la `FETCH`, except does not advance to the next row. Repeated calls to `PEEK` will thus return the same row of data. Returns `NIL` if at EOF. If data is available, returns row data just as `FETCH` (see `FETCH` for data format and conversions done). Optional argument `result-type` is the type of sequence of the column values for the returned row, either `ARRAY` (the default) or `LIST`. `PEEK` is a useful look-ahead for database reporting functions that may need to "break" on changes in data to print headers, summaries, etc.
`(ORACLE:COLUMNS)`

  Returns information on the columns of a SELECT result, in the form of an array of SQLCOL structures, one for each result column in the most recent SELECT statement. It is not necessary to have called `FETCH` before requesting column information on the query, however the query must have been compiled and executed with `RUN-SQL`. Each SQLCOL structure has these slots:

  Slots of `SQLCOL`

  NAME
    The Oracle column name or the expression selected. If the query used a column alias, `SELECT `expr` AS `alias``, then `alias` will be returned as the column name.
  TYPE
    Oracle data type (VARCHAR, NUMBER, DATE, ...)
  SIZE
    Oracle data length (useful mostly for character types)
  SCALE
    For numeric (NUMBER) types, number of digits to right of decimal; NIL for FLOAT
  PRECISION
    For numeric types, total number of significant digits (decimal digits for NUMBER, bits for FLOAT)
  NULL_OK
    `T` if `NULL`s allowed, `NIL` if `NULL`s are not allowed.

  To access the values of the SQLCOL structures, use the standard accessor functions, e.g., `(ORACLE:SQLCOL-NAME (elt (ORACLE:COLUMNS) 0))`

`(ORACLE:EOF)`
  Returns EOF status. A SELECT query cursor is considered at EOF if the next FETCH would return no data. Must be connected to a database, and have an active SELECT statement.
`(ORACLE:INSERT-ROW `table` `values`)`
  Inserts a single row into `table`. Second argument `values` is a map of column names to values: either a hash table whose keys are the column names, or a list of (name, value) pairs. Columns missing from the map will be given the default Oracle value, or `NULL`. Returns the number of rows inserted (i.e., always 1).
`(ORACLE:UPDATE-ROW `table` `condition` `vals` `&OPTIONAL` `params`)`
  Updates rows in `table`. Second argument `condition` is a string expression for a WHERE clause (without the "WHERE") which determines which rows are updated. Third argument `vals` is a map of columns to be updated to their new values: a hash table whose keys are column names, or list of (name, value) pairs. Optional `params` specifies values for named parameters that may occur in `condition`, e.g., when the condition is a match on a primary key, e.g.: `"pk_column = :pk_val"`. Returns the number of rows updated.
`(ORACLE:ROW-COUNT)`
  For SELECT statements, returns the number of rows `FETCH`ed (not `PEEK`ed) so far. For other statements (e.g., INSERT, UPDATE, DELETE), returns the number of rows affected by the last operation (e.g., inserted, updated, deleted). Must be connected to a database and have an active SQL statement.
`(ORACLE:WITH-TRANSACTION `&BODY` `body`)`
  Evaluates the forms in `body` atomically as a database transaction, ensuring that either all the database operations done in `body` complete successfully, or none of them do. If pending (un-committed) changes exist when this macro is entered, they are rolled back (undone), so that the database is affected only by the subsequent updates inside `body`. Nesting of `WITH-TRANSACTION` blocks is not allowed and will raise an error. There is no effect on the status of `auto-commit` given in `ORACLE:CONNECT`; it resumes its previous state when the macro exits. The value of the `WITH-TRANSACTION` expression is that of the last form in `body`.
`(ORACLE:COMMIT)`
  Commits (makes permanent) any pending changes to the database. The `auto-commit` parameter to `ORACLE:CONNECT` must not have been set to use this function, nor can it be called inside a `WITH-TRANSACTION` block. Always returns NIL.
`(ORACLE:ROLLBACK)`
  Rolls back (undoes and abandons) any pending changes to the database. The `auto-commit` parameter to `ORACLE:CONNECT` must not have been set to use this function, nor can it be called inside a `WITH-TRANSACTION` block. Always returns NIL.
`(ORACLE:AUTO-COMMIT)`
  Toggles the state of `auto-commit` initially given to `ORACLE:CONNECT` for the current connection. With `auto-commit` enabled, modifications to the database are committed (made permanent) after each destructive SQL operation made with calls to `RUN-SQL`, `INSERT-ROW`, `UPDATE_ROW`, etc. With `auto-commit` disabled, transactional integrity is under the programmer's control and is managed either by (1) explicitly calling `COMMIT` or `ROLLBACK` to commit or undo the pending operations, or (2) wrapping code blocks with database operations inside the `WITH-TRANSACTION` macro. `AUTO-COMMIT` returns the previous status of `auto-commit`. `AUTO-COMMIT` may not be called inside `WITH-TRANSACTION`.

### 33.10.2. Oracle Example

Below is a simple example script which uses Oracle's demo database schema, `SCOTT`.

    (setf server "orcl") 	; ; Change this to your server's SID
    (oracle:connect "scott" "tiger" server)

    (oracle:run-sql "SELECT deptno, dname, loc FROM dept ORDER BY DNAME")
    (oracle:do-rows (deptno dname loc)
      (format t "Dept. no is '~A', " deptno)
      (format t "Dept. name is '~A', " dname)
      (format t "Dept. loc is '~A'~%" loc))

    (oracle:update-row "dept" "dname = :acctval" '(("dname" "NEWACCT")) '(("acctval" "ACCOUNTING")))

    (oracle:run-sql "SELECT deptno, dname, loc FROM dept ORDER BY DNAME")
    (oracle:do-rows (deptno dname loc)
      (format t "Dept. no is '~A', " deptno)
      (format t "Dept. name is '~A', " dname)
      (format t "Dept. loc is '~A'~%" loc))

    (oracle:update-row "dept" "dname = :acctval" '(("dname" "ACCOUNTING")) '(("acctval" "NEWACCT")))

### 33.10.3. Oracle Configuration

Obviously, a working Oracle environment is required. It is recommended that you first be able to log on and use the Oracle SQL*Plus application to test your environment before attempting Oracle access via the CLISP module. At a minimum you will need to set environment variables `ORACLE_HOME` to the Oracle base directory and `LD_LIBRARY_PATH` to include `$`ORACLE_HOME`/lib` and possibly other directories.

### 33.10.4. Building the Oracle Interface

The module uses the Oracle Call Interface (OCI) C library. To build the module you will need the Oracle OCI headers and link libraries; as a quick check, make sure you have the file `oci.h` somewhere under `ORACLE_HOME`, probably in `$`ORACLE_HOME`/rdbms/demo/oci.h`.

To build the module into CLISP, configure with ./configure ... --with-module=oracle .... The full linking set will contain the module, so you will need to use the `-K` option to use it. You can test that you really have the Oracle-enabled CLISP by evaluating `(`DESCRIBE` 'oracle:connect)`.

### Note

It may be necessary to edit file `modules/oracle/Makefile.in` prior to running ./configure.

## 33.11. LibSVM Interface

This is an “FFI”-based interface to LibSVM.

The package “LIBSVM” is `:CASE-SENSITIVE`, and you do not need the `svm_` prefix.

When this module is present, `*FEATURES*` contains the symbol `:LIBSVM`.

See `modules/libsvm/test.tst` for sample usage.

### 33.11.1. Types

All data is kept on the C side as much as possible, so these foreign types do not have a CLOS counterpart.

node
  Corresponds to svm_node, represented as a `LIST` on the lisp side.
problem
  Corresponds to svm_problem, represented as a `LIST` on the lisp side.
parameter
  Corresponds to svm_parameter, represented as a `VECTOR` on the lisp side.
model
  Corresponds to svm_model, an opaque `FFI:FOREIGN-POINTER`.

### 33.11.2. Output

The output from the library functions goes to `*libsvm-output*`, which is initialized to `*STANDARD-OUTPUT*`.

### 33.11.3. Functions

#### 33.11.3.1. Functions related to problem

`(problem-l `problem`)`
  Return the number of rows in the `problem` (a `FFI:FOREIGN-VARIABLE`)
`(problem-y `problem` `&OPTIONAL` (`length` (problem-l `problem`)))`
  Return a `(`VECTOR` `DOUBLE-FLOAT` `length`)` representing the targets in the `problem` (a `FFI:FOREIGN-VARIABLE`).
`(problem-y-n `problem` `n` `&OPTIONAL` (`length` (problem-l `problem`))))`
  Return the `DOUBLE-FLOAT` representing the `n`th target in the `problem` (a `FFI:FOREIGN-VARIABLE`).
`(problem-x `problem` `&OPTIONAL` (`length` (problem-l `problem`)))`
  Return a `(`VECTOR` (`VECTOR` node) `length`)` representing the predictors in the `problem` (a `FFI:FOREIGN-VARIABLE`).
`(problem-x-n `problem` `n` `&OPTIONAL` (`length` (problem-l `problem`))))`
  Return the `(`VECTOR` node)` representing the `n`th set of predictors in the `problem` (a `FFI:FOREIGN-VARIABLE`).
`(make-problem `&KEY` `l` `y` `x`)`
  Allocate a `FFI:FOREIGN-VARIABLE` representing a model.
`(destroy-problem `problem`)`

  Release the memory taken by the problem object and invalidate the `FFI:FOREIGN-VARIABLE` `problem`.

  ### Warning

  You must call this function yourself, but only after deallocating all model objects trained from this `problem`.

`(load-problem `filename` `&KEY` (`log` `*STANDARD-OUTPUT*`))`

  Read a problem from a file in the libsvm/svmlight format. Return two values: the problem and max index (i.e., the number of columns).

  Messages go to `log`.

`(save-problem `filename` `problem` `&KEY` (`log` `*STANDARD-OUTPUT*`))`

  Write a problem into a file.

  Messages go to `log`.

#### 33.11.3.2. Functions related to model

`(destroy-model `model`)`

  Release the memory taken by the model object and invalidate the `FFI:FOREIGN-VARIABLE` `model`.

  Calls `svm_destroy_model` or `svm_svm_free_and_destroy_model`.

  You do not have to call this function yourself, it is attached to the `model` by `train` and `load-model` via `EXT:FINALIZE`.

`(check-parameter `problem` `parameter`)`

  Check if the `parameter` is appropriate for the `problem`.

  Calls `svm_check_parameter`.

`(train `problem` `parameter`)`

  Train a model.

  Calls `svm_train` and `check-parameter`.

`(cross-validation `problem` `parameter` `n`)`

  Run `n`-fold cross-validation.

  Calls `svm_cross_validation` and `check-parameter`.

`(save-model `filename` `model`)`

  Write a model into a file.

  Calls `svm_save_model`.

`(load-model `filename`)`

  Read a model from a file.

  Calls `svm_load_model`.

`(get-svm-type `model`)`
  Call `svm_get_svm_type`.
`(get-nr-class `model`)`
  Call `svm_get_nr_class`.
`(get-labels `model`)`
  Call `svm_get_labels`.
`(get-svr-probability `model`)`
  Call `svm_get_svr_probability`.
`(predict-values `model` `x`)`

  Return the decision values (a `(`VECTOR` `DOUBLE-FLOAT`)`) given by `model` for `x` (a `(`VECTOR` node)`).

  Calls `svm_predict_values`.

`(predict `model` `x`)`
  Call `svm_predict`.
`(predict-probability `model` `x`)`
  Call `svm_predict_probability`.
`(check-probability-model `model`)`
  Call `svm_check_probability_model`.

#### 33.11.3.3. Functions related to parameter

`(destroy-parameter `parameter`)`

  Release the memory taken by the parameter object and invalidate the `FFI:FOREIGN-VARIABLE` `parameter`.

  Does not call `svm_destroy_param`.

  You do not have to call this function yourself, it is attached to the `parameter` by `make-parameter` via `EXT:FINALIZE`.

`(make-parameter `&KEY` :v svm_type kernel_type degree gamma coef0 cache_size eps C nr_weight weight_label weight nu p shrinking probability)`

  Allocates a new `FFI:FOREIGN-VARIABLE` of type parameter with the supplied slots.

  The defaults come from vector `v` (such as returned by `(`FFI:FOREIGN-VALUE` `parameter`)`), if supplied, providing an easy way to copy `parameter`s, otherwise the defaults for svm-train are used.

`(parameter-alist `parameter`)`
  Return the association list representing `parameter`.

## 33.12. Computer Algebra System PARI

This package offers an “FFI”-based interface to PARI.

The package “PARI” is `:CASE-SENSITIVE`.

When this module is present, `*FEATURES*` contains the symbol `:PARI`.

PARI objects are printed and read using a special `#Z""` syntax.

Most functions accept lisp objects as well as PARI objects and return PARI objects, which can be converted to lisp using the `pari:pari-to-lisp` function.

See `modules/pari/test.tst` for sample usage.

### Available functionality

The module interfaces to most of the functions available in GP, by parsing the file `${prefix}/share/pari/pari.desc`, see `modules/pari/desc2lisp.lisp`.

Lisp functions are normally named the same as the GP functions they correspond to or the PARI functions they call, e.g.:

- `para:quadpoly` corresponds to the eponymous GP function and calls the `quadpoly0` PARI function
- `para:issmall` calls the PARI function `issmall` which has no GP analogue
- `para:random_` (note the `_` suffix to avoid clash with the [ANSI CL standard] `RANDOM`) corresponds to the GP function `random` and calls the `genrand` PARI function.

### Extending the module

Not all PARI functions have a corresponding Lisp function, but one can remedy that with just a few lines:

    (FFI:DEFAULT-FOREIGN-LIBRARY "libpari.so") ; or pari.dll on Win32
    (pari:pari-call-out (matrix-rank ffi:long) "rank" (x))	; long rank(GEN x);
    (pari:pari-call-out fibonacci "fibo" ((n ffi:long)))	; GEN fibo(long n);
    (pari:pari-call-out-prec pari-arctan "gatan" (x))	; GEN gatan(GEN x, long prec);
    (pari:pari-call-out (equal? boolean) "gequal" (x y))	; GEN gequal(GEN x, GEN y);

(Actually, these four functions are already interfaced to by the module.) Please feel free to submit additions for `modules/pari/pari.lisp` and `modules/pari/test.tst`.

### Real precision

The real precision defaults to `pari:pari-real-precision` which specifies the default precision in decimal digits:

    pari:pari-real-precision
    ⇒ 19
    (LENGTH (PRIN1-TO-STRING (pari:pari-to-lisp (pari:Pi))))
    ⇒ 23

One can also pass the precision parameter explicitly:

    (LENGTH (PRIN1-TO-STRING (pari:pari-to-lisp (pari:Pi :prec 38))))
    ⇒ 41

Note that the actual precision is determined by the size of the mantissa which can be incremented only in steps of `(`FFI:BITSIZEOF` 'ffi:ulong)` (64 bits or 32 bits).

## 33.13. Matlab Interface

This is an interface to the Matlab C API.

The package “MATLAB” is `:CASE-SENSITIVE`, so you would write `(matlab:engOpen ...)` when you need to call `engOpen`.

When this module is present, `*FEATURES*` contains the symbol `:MATLAB`.

Additionally, some higher level functionality is available (see `modules/matlab/test.tst` for sample usage):

`(matlab:matfile-content mf)`
  Return a `VECTOR` of `STRING`s naming the variables in file `mf` (opened using `matOpen`).
`matlab:*command*`
  The default argument to `engOpen`.
`matlab:*engine*`
  The currrently open Matlab engine.
`(matlab:engine)`
  Make sure `*engine*` is valid and return it.
`(matlab:with-engine (`&OPTIONAL` engine command) `&BODY` `body`)`
  Run the `body` wuth the `engine` bound to a Matlab engine (default `*engine*`). The engine is opened with `engOpen`, then closed with `engClose`.
`(matlab:with-MATfile (file name `&OPTIONAL` mode) `&BODY` `body`)`
  `matOpen` the matlab file, do the `body`, `matClose` it.
`(matlab:copy-lisp-to-mxArray lisp-array `&OPTIONAL` matlab-matrix)`
  Copy data from the 2-dimensional lisp array to the Matlab matrix.
`(matlab:copy-lisp-to-matlab lisp-array matlab-variable `&KEY` engine)`
  Copy the 2-dimensional lisp array to the Matlab variable (a `STRING`) in the supplied engine (defaults to `*engine*`).
`(matlab:copy-mxArray-to-lisp matlab-matrix `&OPTIONAL` lisp-array)`
  Copy the matlab matrix to the 2-dimensional lisp array (created anew or re-used if supplied).
`(matlab:copy-matlab-to-lisp matlab-variable `&OPTIONAL` lisp-array `&KEY` engine)`
  Copy data from the matlab variable to the 2-dimensional lisp array (created anew or re-used if supplied).
`(matlab:invert-matrix lisp-array `&KEY` engine)`
  Invert the lisp matrix using the specified engine.

## 33.14. Netica Interface

This is an interface to the Netica C API (C API version 3.25) for working with Bayesian belief networks and influence diagrams.

The package “NETICA” is `:CASE-SENSITIVE`, e.g., you would write `(netica:GetNodeExpectedUtils_bn ...)` when you need to call `GetNodeExpectedUtils_bn`.

When this module is present, `*FEATURES*` contains the symbol `:NETICA`.

All public C functions are available as `FFI:FOREIGN-FUNCTION`s.

The functions which are specified to return C arrays, namely

`GetNodeBeliefs_bn`
`GetNodeExpectedUtils_bn`
`GetNodeLikelihood_bn`
`GetNodeProbs_bn`
`GetNodeLevels_bn`

correspond to `FFI:FOREIGN-FUNCTION`s which return FFI:C-POINTERs. We define low level wrappers for them, namely

`GetNodeBeliefs`
`GetNodeExpectedUtils`
`GetNodeLikelihood`
`GetNodeProbs`
`GetNodeLevels`

which return the appropriate `VECTOR`s.

Additionally, some higher level functionality is available (see `modules/netica/demo.lisp` for sample usage):

`(netica:start-netica `&KEY` :license :verbose)`
  Call `NewNeticaEnviron_ns` and `InitNetica2_bn` and print some statistics; initialize `netica:*env*`.
`(netica:check-errors `&KEY` :env :clear :severity)`
  Show and, optionally, clear (`ClearError_ns`), the errors of the given severity (`ErrorSeverity_ns`) and above. You should call this function after every call to a Netica function. Every wrapper function in this list calls it, so you do not need to call it after a call to a wrapper function.
`(netica:error-message error)`

  Convert netica error to a `STRING` containing

  `ErrorCategory_ns`
  `ErrorSeverity_ns`
  `ErrorNumber_ns`
  `ErrorMessage_ns`

`(netica:close-netica `&KEY` :env :verbose)`
  Terminate the Netica session. Sets `netica:*env*` to `NIL`.
`(netica:make-net `&KEY` :name :comment :title :env :verbose)`
  Call `NewNet_bn`, `SetNetTitle_bn` and `SetNetComment_bn`.
`(netica:net-info net `&KEY` :out)`

  Print some information about the net:

  `GetNetName_bn`
  `GetNetTitle_bn`
  `GetNetComment_bn`
  `GetNetFileName_bn`
  `GetNetNodes_bn`

`(netica:make-node `&KEY` :name :net :kind :levels :states :num-states :title :comment :parents :cpt :x :y :env :verbose)`
  Call `NewNode_bn` with the given name and many other parameters.
`(netica:node-info node `&KEY` :header :out)`
  Print some information about the node, preceded by the header.
`(netica:get-beliefs node `&KEY` :env :verbose)`
  Call `GetNodeBeliefs_bn` on the node and pretty-print the results when `:VERBOSE` is non-`NIL`.
`(netica:enter-finding net node state `&KEY` :env :verbose)`
  Call `EnterFinding_bn` using `GetNodeNamed_bn` and `GetStateNamed_bn`.
`(netica:save-net net `&KEY` :file :env :verbose)`
  Call `WriteNet_bn`.
`(netica:read-net file `&KEY` :env :verbose)`
  Call `ReadNet_bn`.
`(netica:with-open-dne-file (var file `&REST` opts) `&BODY` body)`
  Call `NewFileStream_ns`, execute `body`, then `DeleteStream_ns` - just like `WITH-OPEN-STREAM`.
`netica:*verbose*`
  The log `STREAM` or `NIL`; the default value for the `:VERBOSE` argument (initially set to `NIL`).
`netica:*license*`
  The license key provided by Norsys; the default value for the `:LICENSE` argument.
`netica:*env*`
  The Netica environment object; the default value for the `:ENV` argument.

## 33.15. Perl Compatible Regular Expressions

This is an interface to Perl Compatible Regular Expressions.

When this module is present, `*FEATURES*` contains the symbol `:PCRE`.

PCRE module API

`(PCRE:PCRE-VERSION)`
  Return version information as 4 values: descriptive `STRING`; 2 `FIXNUM`s: major and minor numbers; date `STRING`.
`(PCRE:PCRE-CONFIG `type`)`

  Return some information about the PCRE build configuration. `type` is one of

  `:UTF8`
  `:NEWLINE`
  `:LINK-SIZE`
  `:POSIX-MALLOC-THRESHOLD`
  `:MATCH-LIMIT`
  `:STACKRECURSE`
  `:UNICODE-PROPERTIES`
  `:MATCH-LIMIT-RECURSION`
  `:BSR`

`(PCRE:PCRE-COMPILE `string` `&KEY` :STUDY :IGNORE-CASE :MULTILINE :DOTALL :EXTENDED :ANCHORED :DOLLAR-ENDONLY :EXTRA :NOTBOL :NOTEOL :UNGREEDY :NOTEMPTY :NO-AUTO-CAPTURE)`
  Compile a pattern, optionally study it.
`(PCRE:PATTERN-INFO `pattern` `&OPTIONAL` request)`

  Return some information about the `pattern`, such as

  `:OPTIONS`
  `:SIZE`
  `:CAPTURECOUNT`
  `:BACKREFMAX`
  `:FIRSTBYTE`
  `:FIRSTTABLE`
  `:LASTLITERAL`
  `:NAMEENTRYSIZE`
  `:NAMECOUNT`
  `:NAMETABLE`
  `:STUDYSIZE`
  `:OKPARTIAL`
  `:JCHANGED`
  `:HASCRORLF`
  `:MINLENGTH`

`(PCRE:PCRE-NAME-TO-INDEX `pattern` `name`)`
  Convert the name of the sub-pattern to an index in the return vector.
`(PCRE:PCRE-EXEC `pattern` `string` `&KEY` :WORK-SPACE :DFA :BOOLEAN :OFFSET :ANCHORED :NOTBOL :NOTEOL :NOTEMPTY :PARTIAL :DFA-SHORTEST :DFA-RESTART :FIRSTLINE :DUPNAMES :NEWLINE-CR :NEWLINE-LF :NEWLINE-CRLF :NEWLINE-ANY :NEWLINE-ANYCRLF :BSR-ANYCRLF :BSR-UNICODE :JAVASCRIPT-COMPAT :NO-START-OPTIMIZE :NO-START-OPTIMISE :PARTIAL-HARD :NOTEMPTY-ATSTART)`

  Execute the compiled `pattern` against the `string` at the given `offset` with the given options. Returns `NIL` if no matches or a `VECTOR` of `LENGTH` `CAPTURECOUNT+1` of PCRE:MATCH structures, unless `:BOOLEAN` was non-`NIL`, in which case return `T` as an indicator of success, but do not allocate anything.

  `:DFA` argument determines whether `pcre_dfa_exec` is used instead of `pcre_exec` (PCRE v6 and better).

  `:WORK-SPACE` is only used for `:DFA` and defaults to 20.

`(PCRE:MATCH-START `match`)`
`(PCRE:MATCH-END `match`)`
  Return the start and end of the `match`. `SETF`-able.
`(PCRE:MATCH-SUBSTRING `match` `string`)`
  Return the substring of `string` bounded by `match`.
`(PCRE:MATCH-STRINGS return-vector `string`)`
  Return all substrings for all matches found by `PCRE:PCRE-EXEC`.
`(PCRE:MATCH-STRING return-vector which `string` `&OPTIONAL` `pattern`)`
  Return the substring that matches the given sub-pattern. If `which` is a name of the sub-pattern (as opposed to its number), `pattern` must be supplied.
`(PCRE:PCRE-MATCHER `pattern`)`
  A valid value for `CUSTOM:*APROPOS-MATCHER*`.

## 33.16. Interface to zlib

This is an “FFI”-based interface to the ZLIB.

When this module is present, `*FEATURES*` contains the symbol `:ZLIB`.

`(ZLIB:Z-VERSION)`
  Return the string version of the underlying library.
`(ZLIB:COMPRESS source `&KEY` level)`
  Compress the `source` `VECTOR`.
`(ZLIB:UNCOMPRESS source destination-length)`
  Uncompress the `source` `VECTOR` (returned by `ZLIB:COMPRESS`). `destination-length` should be no less than the length of the uncompressed `source`.
`(ZLIB:COMPRESS-BOUND source-length)`
  Return the maximum length of the return value of `ZLIB:COMPRESS`.
`(ZLIB:ERROR-STRING `error-code`)`
  Return a descriptive string for the supplied `error-code`.
`ZLIB:ZERROR`
  An `ERROR` sometimes `SIGNAL`ed by `ZLIB:COMPRESS` and `ZLIB:UNCOMPRESS`. You can find the error code and the caller using `ZLIB:ZERROR-ERRNO` and `ZLIB:ZERROR-CALLER`.

## 33.17. Raw Socket Access

### 33.17.1. Introduction

This is the raw socket interface, as described in <`sys/socket.h`>. Sockets are represented by their `FIXNUM` file descriptors.

When this module is present, `*FEATURES*` contains the symbol `:RAWSOCK`.

### Try `SOCKET:SOCKET-STREAM` first!

For most uses of sockets, the facilities described in Section 32.4, “Socket Streams” are adequate and much more convenient than these. You are encouraged to consider `SOCKET:SOCKET-STREAM`s and ensure that they are not adequate for your purposes before you use raw sockets.

### Do not use `EXT:MAKE-STREAM`!

You can turn such a raw socket into a usual lisp `STREAM` using `EXT:MAKE-STREAM`, but you should be extremely careful with such dubious actions! See the clisp-devel mailing list archives for more details. Note that `EXT:MAKE-STREAM` will duplicate the file descriptor (using `dup`), so you still have to `CLOSE` the original raw socket.

Test file `modules/rawsock/test.tst` and the demos in `modules/rawsock/demos/` contain plenty of examples.

### 33.17.2. Single System Call Functions

We implement access to

`(`accept` `socket` `address`)`
`(`bind` `socket` `address`)`
`(`connect` `socket` `address`)`
`(`getaddrinfo` `&KEY` node service protocol socktype family passive canonname numerichost numericserv v4mapped all addrconfig)`
`(`getnameinfo` `address` `&KEY` nofqdn numerichost namereqd numericserv numericscope dgram)`
`(`getpeername` `socket` `address`)`
`(`getsockname` `socket` `address`)`
`(`htonl` `n`)`
`(`htons` `n`)`
`(`ntohl` `n`)`
`(`ntohs` `n`)`
`(`recv` `socket` `buffer` `&KEY` start end peek oob waitall)`
`(`recvfrom` `socket` `buffer` `address` `&KEY` start end peek oob waitall)`
`(`recvmsg` `socket` `message` `&KEY` start end peek oob waitall)`
`(`send` `socket` `buffer` `&KEY` start end oob eor)`
`(`sendmsg` `socket` `message` `&KEY` start end oob eor)`
`(`sendto` `socket` `buffer` `address` `&KEY` start end oob eor)`
`(`sockatmark` `socket`)`
`(`socket` `domain` `type` `protocol`)`
`(`socketpair` `domain` `type` `protocol`)`

using same-named lisp functions in package “RAWSOCK”. Additionally,

`(`RAWSOCK:SOCK-CLOSE` `socket`)` calls `close`.
`(`RAWSOCK:SOCK-LISTEN` `socket` `&OPTIONAL` (`backlog` SOMAXCONN))` calls `listen`.

### Note

When the OS does not provide `socketpair`, it is emulated using `socket` + `connect` + `accept`.

### 33.17.3. Common arguments

void* `buffer`
  A `(`VECTOR` (`UNSIGNED-BYTE` 8))`. The vector may be adjustable and have a fill pointer. Whenever a function accepts a `buffer` argument, it also accepts `:START` and `:END` keyword arguments with the usual meaning and defaults. You do not have to supply the vector length because Lisp can determine it itself, but, if you want to, you can use `:END` argument for that.
int `socket`
  An `INTEGER` (returned by `socketpair` or `socket`).
int `family`
int `domain`
  A `NIL` (stands for `AF_UNSPEC`), `INTEGER`, or a platform-specific keyword, e.g., `:INET` stands for `AF_INET`.
int `type`
  A `NIL` (stands for 0); `INTEGER`; or a platform-specific keyword, e.g., `:DGRAM` stands for `SOCK_DGRAM`.
int `protocol`
  A `NIL` (stands for 0); `INTEGER`; a platform-specific keyword, e.g., `:ETH_P_ARP` stands for `ETH_P_ARP`, `:IPPROTO-ICMP` stands for `IPPROTO_ICMP`; or a `STRING` (passed to `getprotobyname`).
int `flags`
  This C argument corresponds to keyword arguments to the Lisp functions. E.g., `rawsock:send` accepts `:OOB` and `:EOR` arguments, while `rawsock:recv` accepts `:PEEK`, `:OOB` and `:WAITALL`.
struct sockaddr `address`
  A `STRUCTURE-OBJECT` RAWSOCK:SOCKADDR returned by `MAKE-SOCKADDR`.
struct msghdr `message`

  A `STRUCTURE-OBJECT` RAWSOCK:MESSAGE with the following slots:

  addr | a SOCKADDR.
  iovec | a `(`VECTOR` `(`VECTOR` (`UNSIGNED-BYTE` 8))`)` (`:START` and `:END` arguments are applied to this vector)
  control | a `(`VECTOR` (`UNSIGNED-BYTE` 8))`
  flags | a `LIST`

#### 33.17.3.1. Platform-dependent Keywords

One can extract the list of acceptable platform-dependent keywords for, e.g., socket domain, using the following code:

     (BLOCK NIL
       (HANDLER-BIND ((TYPE-ERROR
                        (LAMBDA (c)
                          (FORMAT T "~&error: ~A~%" c)
                          (RETURN (CDDR (THIRD (TYPE-ERROR-EXPECTED-TYPE c)))))))
         (rawsock:socket "bad" NIL NIL)))

### 33.17.4. Return Values

The return values of the functions described in section Section 33.17.2, “Single System Call Functions” are derived from the return values of the underlying system call: if, say, the `address` argument is modified by the system call, two values are returned (in addition to the possible values coming from the return value of the system call): the (modified) `address` structure and its new size. If the system call fails, an `ERROR` is `SIGNAL`ed.

### 33.17.5. Not Implemented

We do not interface to `select` or `poll` in this module, they are already available through `SOCKET:SOCKET-STATUS`.

We do not interface to `shutdown` in this module, it is already available through `SOCKET:SOCKET-STREAM-SHUTDOWN`.

### 33.17.6. Errors

Errors in `getaddrinfo` and `getnameinfo` are `SIGNAL`ed as `CONDITION`s of type RAWSOCK:EAI using `gai_strerror`.

Errors in other functions are reported as the usual OS errors (using `strerror`).

### 33.17.7. High-Level Functions

Functions that do not correspond to a single system call

`(`RAWSOCK:SOCK-READ` `socket` `buffer` `&KEY` start end)`
`(`RAWSOCK:SOCK-WRITE` `socket` `buffer` `&KEY` start end)`

  Call one of `read`/`readv` or `write`/`writev` (depending on whether `buffer` is a `(`VECTOR` (`UNSIGNED-BYTE` 8))` or a `(`VECTOR` `(`VECTOR` (`UNSIGNED-BYTE` 8))`)`). Return the number of bytes read or written.

  When `readv` and `writev` and not available, they are emulated by repeated calls to `read` and `write`.

  On Win32 we have to use `recv` instead of `read` and `send` instead of `write` because Win32 `read` and `write` do not work on sockets, only on regular files.

`(RAWSOCK:PROTOCOL `&OPTIONAL` `protocol`)`
  Call `getprotobyname` when `protocol` is a `STRING`, or call `getprotobynumber` when `protocol` is an `INTEGER`. Return a RAWSOCK:PROTOCOL structure object. When `protocol` is `NIL`, return a `LIST` of all known protocols using `setprotoent`, `getprotoent`, and `endprotoent`.
`(RAWSOCK:NETWORK `&OPTIONAL` `network` `type`)`
  Call `getnetbyname` when `network` is a `STRING`, or call `getnetbyaddr` when `network` is an `INTEGER`. Return a RAWSOCK:NETWORK structure object. When `network` is `NIL`, return a `LIST` of all known networks using `setnetent`, `getnetent`, and `endnetent`.
`(RAWSOCK:IF-NAME-INDEX `&OPTIONAL` `what`)`
  Call `if_nametoindex` when `what` is a `STRING` and return an `INTEGER`; or call `if_indextoname` when `what` is an `INTEGER` and return a `STRING`. When `what` is `NIL`, return an association list of pairs `(`index` . `name`)` using `if_nameindex`.
`(RAWSOCK:IFADDRS `&KEY` :FLAGS-OR :FLAGS-AND)`
  Call `getifaddrs` and return a `LIST` of ifaddrs objects, optionally filtered using flags, e.g., `(ifaddrs :flags-or '(`k` `l`) :flags-and '(`m` `n`))` will return a list of objects which have both flags `m` and `n` and at least one of `k` or `l` set.
`(RAWSOCK:SOCKET-OPTION `socket` `name` `&KEY` :LEVEL)`
`(`SETF` (RAWSOCK:SOCKET-OPTION `socket` `name` `&KEY` :LEVEL) `value`)`
  Call `getsockopt` and `setsockopt`, returns and sets individual (for specific option `name` and `level`) and multiple (when `name` is `NIL` and/or `level` is `:ALL`) options. (See also `SOCKET:SOCKET-OPTIONS`.)
`(`RAWSOCK:CONVERT-ADDRESS` `family` `address`)`

  Convert between `STRING` and `(`VECTOR` (`UNSIGNED-BYTE` 8))` `IP` `address` representations using

  `inet_addr` | `inet_ntop`
  `inet_ntoa` | `inet_pton`

  (`INTEGER`s are also accepted for backward compatibility)

`(RAWSOCK:MAKE-SOCKADDR `family` `&OPTIONAL` `data`)`

  Create a sockaddr object. `data` should be a sequence of `(`UNSIGNED-BYTE` 8)` or an `INTEGER` (meaning `(`MAKE-LIST` `data` :initial-element 0)`). When omitted, the standard platform-specific size is used.

  ### Note

  It is critical to use `data` of the corrent size (usually `sizeof(struct sockaddr)`, but may be something depending on the protocol to be used).

`(RAWSOCK:SOCKADDR-FAMILY `address`)`
  Return the symbolic `family` of the sockaddr object.
`(RAWSOCK:SOCKADDR-DATA `address`)`

  Return a fresh `VECTOR` displaced to the `data` field of the C struct sockaddr object.

  ### Warning

  Modifying this `VECTOR`'s content will modify the `address` argument data!

`(RAWSOCK:OPEN-UNIX-SOCKET `pathname` `&OPTIONAL` (`type` `:STREAM`))`
  Open a UNIX socket special file. Returns two values: `socket` and `address`.
`(RAWSOCK:OPEN-UNIX-SOCKET-STREAM `pathname` `&REST` `options` `&KEY` (`type` `:STREAM`) `&ALLOW-OTHER-KEYS`)`
  Open a UNIX socket special file. Returns two values: `stream` and `address`. `type` is passed to `RAWSOCK:OPEN-UNIX-SOCKET`, other `options` to `EXT:MAKE-STREAM` (but see Do not use `EXT:MAKE-STREAM`!).
`(RAWSOCK:IPCSUM `buffer` `&KEY` start end)` - `IP`
`(RAWSOCK:ICMPCSUM `buffer` `&KEY` start end)` - `ICMP`
`(RAWSOCK:TCPCSUM `buffer` `&KEY` start end)` - `TCP`
`(RAWSOCK:UDPCSUM `buffer` `&KEY` start end)` - `UDP`

  Compute the appropriate protocol checksum and record it in the appropriate location. `buffer` is assumed to be a suitable ethernet frame for the protocol, with the appropriate header etc.

  Note that `buffer` is an ethernet frame, starting with 6 bytes of the destination MAC address, 6 bytes of the source MAC address, and 2 bytes specifying the next level protocol, (e.g., `#x0800` for `IP` and `#x0806` for `ARP`), i.e., the first 14 bytes of `buffer` are ignored by these functions.

  A typical packet you send is both `IP` and `TCP` and thus has two checksums, so you would want to call two functions.

`(RAWSOCK:CONFIGDEV `socket` `ifname` `address` `&KEY` `promisc` `noarp`)`
  Set some socket options and `IP` `address` with `ioctl`.

## 33.18. The FastCGI Interface

The FastCGI module speeds up CLISP CGI scripts launched by a Web server. Working with a FastCGI-enabled Web server such as Apache with mod_fastcgi, a CLISP program using the FastCGI protocol will run many times faster than a conventional CGI program. The performance improvements stem from the fact that the script's process remains running across HTTP requests, eliminating startup overhead and allowing for caching of data structures and other resources. This is the same approach used is in other languages (e.g., mod_perl for Perl).

When this module is present, `*FEATURES*` contains the symbol `:FASTCGI`.

### 33.18.1. Overview of FastCGI

Traditional CGI programs work by doing input/output with the Web server via the following channels:

1. Examining environment variables; e.g., `HTTP_USER_AGENT` is the variable set by the Web server to name the browser used
2. Reading from standard input. E.g., to get input data in a "method=POST" request
3. Writing an HTTP response document (usually "Content-type: text/html") to the standard output, for eventual transmission back to the browser client
4. Writing error messages to the standard error, usually captured by the Web server and logged in its log files.

FastCGI involves replacing calls the standard routines to do the above with calls in the “FASTCGI” package. These calls will then work exactly as before when the program is invoked as a CGI, but will also work when invoked by a FastCGI-enabled Web server.

FastCGI programs persist across HTTP requests, and thus incur startup overhead costs only once. For Lisp Web programs, this overhead can be substantial: code must be compiled and loaded, files and databases must be opened, etc. Further, because the program stays running from HTTP request to HTTP request, it can cache information in memory such as database connections or large in-memory data structures.

### 33.18.2. Functions in Package “FASTCGI”

Access to FastCGI is via these functions in package “FASTCGI”.

`(FASTCGI:IS-CGI)`
  Returns `T` if the CLISP program has been launched as a traditional CGI rather than in FastCGI. In traditional CGI, program I/O is via operating system environment variables and standard file streams. Under FastCGI, I/O is done directly with the Web server via the FastCGI protocol.
`(FASTCGI:ACCEPT)` `cgi-forms` `(FASTCGI:FINISH)`

  In FastCGI mode, the program loops, `ACCEPT`ing to begin the execution of an HTTP request, and `FINISH`ing to signal that the script is finished writing its response to the HTTP request. `ACCEPT` blocks until the next HTTP request comes in, returning `T` if there is a new request to handle, and `NIL` if no more HTTP requests will occur, usually because the Web server itself has terminated, in which case the FastCGI server loop should also exit.

  A typical FastCGI top-level server loop looks like:

      (do ()
          ((not (fastcgi:accept)))
        (run-my-script)
        (fastcgi:finish))

`(FASTCGI:GETENV `varname`)`
  Use in place of `EXT:GETENV` to get the value of the environment variable named `varname`, which should be a string. Unlike `EXT:GETENV`, which accesses the actual host operating system environment, `FASTCGI:GETENV` obtains its environment via the Web server, over its FastCGI communications channel. For more information, see the FastCGI Web site. Returns `NIL` if `varname` is not defined in the operating system environment. See here for a list of useful variables. You must first have called `ACCEPT` and not yet have called `FINISH`.
`(FASTCGI:WRITE-STDOUT `string`)`
  Use in place of standard Lisp calls which print to standard output (i.e., as part of the HTTP response). You must first have called `ACCEPT` and not yet have called `FINISH`.
`(FASTCGI:WRITE-STDERR `string`)`
  Use in place of standard Lisp calls which print to standard error. Rather than being part of the HTTP response, data written to standard error are usually collected by the Web server in its error log. This is useful for diagnostic purposes.
`(FASTCGI:SLURP-STDIN)`
  Reads in the entirety of standard input and returns it as a string. This is usually done for HTTP requests with `METHOD="post"`, when the data are passed to the CGI script via standard input rather than via the environment variable `QUERY_STRING`. There is no way to read standard input in pieces, which could be a problem, say, for HTTP uploads of very large files.
`(FASTCGI:OUT `tree`)`
  Like `WRITE-STDOUT`, except that `tree` may be an arbitrarily nested list structure containing (at the leaves) numbers and strings. For example, `(FASTCGI:OUT '("foo" (" " 10 " " 20)))` will write the string `"foo 10 20"`. This function is useful when building strings in memory for display.

### 33.18.3. FastCGI Example

Below is a simple example CGI script using FastCGI.

    #!/usr/local/bin/clisp -q -K full

    (do ((count 1 (1+ count)))
        ((not (fastcgi:accept)) nil)
      (fastcgi:out "Content-type: text/plain" #\Newline #\Newline)
      (fastcgi:out
       "I am running in mode: " (if (fastcgi:is-cgi) "CGI" "FastCGI") #\Newline
       "This is execution no.: " count #\Newline
       "The browser string is '" (fastcgi:getenv "HTTP_USER_AGENT") "'" #\Newline)
      (fastcgi:finish))

### 33.18.4. Building and configuring the FastCGI Interface

It is necessary to download the FastCGI developers' kit, build it, and install it, before building CLISP with FastCGI support. You also need to upgrade your Web server to speak the FastCGI protocol. For Apache this means building in mod_fastcgi, either statically or dynamically, and then adding a line to your Apache config like:

         Addhandler fastcgi-script .fcgi

After that, you can convert `foo.cgi` by linking it to a script names `foo.fcgi`. Since a FastCGI script is also a valid CGI script, it can be run unmodified in either mode.

## 33.19. Interface to D-Bus

This is an “FFI”-based interface to the D-Bus message bus system, a simple way for applications to talk to one another.

The package “DBUS” is `:CASE-SENSITIVE`, e.g., you would write `(dbus:dbus_error_init ...)` when you need to call the C function `dbus_error_init`.

When this module is present, `*FEATURES*` contains the symbol `:D-BUS`.

All public C functions are available as `FFI:FOREIGN-FUNCTION`s, defined in `modules/dbus/dbus.lisp`.

See `modules/dbus/test.tst` for sample usage.

## 33.20. GTK Interface

This is an “FFI”-based interface to GTK+ version 2.

The package “GTK” is `:CASE-SENSITIVE`.

When this module is present, `*FEATURES*` contains the symbol `:GTK`.

### 33.20.1. High-level functions

`(glade-load `filename`)`
  Load and connect the UI described in the Glade-generated file `filename`.
`(run-glade-file `filename` `name`)`
  Run the widget `name` described in the Glade-generated file `filename`.
`(gui `filename`)`
  Run the CLISP demo GUI described in the Glade-generated file `filename`, normally a variation of `modules/gtk2/ui.glade`.

# Part IV. Internals of the CLISP Implementation

## Chapter 34. The source files of CLISP

For files in CLISP binary distributions, see the section called “Files”.

## 34.1. File Types

`#P"*.d"`
  The source files for unpreprocessed C code.
`#P".c"`
  The C code after preprocessing; also the result of compiling some “FFI” forms (see `FFI:*OUTPUT-C-FUNCTIONS*`).
`#P".lisp"`
  The source files for Lisp code.
`#P"*.fas"`
  Compiled lisp code (platform-independent bytecodes).
`#P".lib"`
  Lisp “header”, produced by `COMPILE-FILE` and used by `REQUIRE`

## 34.2. Source Pre-Processing

C sources are pre-processed with the following tools before being passed to the C compiler:

`utils/comment5.c`

  Convert /bin/sh-style comments (lines starting with `"# "`) to C-style comments (`/**/`).

  ### Warning

  The use of /bin/sh-style comments is deprecated.

`utils/comment5.sed`
  A GNU sed script that converts /bin/sh-style comments (lines starting with `"# "`) to C-style comments (`/**/`). Functionally equivalent to `utils/comment5.c`.
`utils/varbrace.c`
  Add braces to C source code, so that variable declarations (introduced with the pseudo-keyword `var`) can be used within blocks, like in C++ and C99.
`utils/ccpaux.c`
  When cpp cannot handle indented directives, remove the indentation.
`utils/gctrigger.c`
  Add `GCTRIGGER` statements at the head of function bodies (for functions marked with the `maygc` pseudo-keyword).
`utils/deema.c`
  When cpp cannot handle empty macro arguments, insert `_EMA_` instead.
`utils/ccmp2c.c`
  For the `clx/new-clx` module only. Allows cpp-style preprocessing before modprep processing. Should be merged into modprep eventually.
`utils/modprep.lisp`
  For some modules only, see Section 32.2.7.1, “Modprep”.
`utils/unicode/`

  Generate NLS files in `src/`.

  `utils/unicode/UnicodeDataFull.txt`
    Character descriptions from Unicode 3.2; used by `DESCRIBE` and installed in `data/` under `CUSTOM:*LIB-DIRECTORY*`.

## 34.3. Files

### 34.3.1. Unpreprocessed C code

#### 34.3.1.1. Includes

`src/lispbibl.d`
  main include file
`src/fsubr.d`
  list of all built-in special forms
`src/subr.d`
  list of all built-in functions
`src/pseudofun.d`
  list of all “pseudo functions”
`src/constpack.d`
  list of packages accessed by C code
`src/constsym.d`
  list of symbols accessed by C code
`src/constobj.d`
  list of miscellaneous objects accessed by C code
`src/unix.d`
  include file for the UNIX implementations
`src/win32.d`
  include file for the Win32 based versions
`src/xthread.d`
  include file for thread support
`build/modules.h`
  list of foreign modules, generated at build time

#### 34.3.1.2. Internal C Modules

`src/spvw.d`

  Memory management (garbage-collection), startup; some OS interface.

  `src/avl.d`
    An implementation of AVL (Adelson-Velskii and Landis) trees.
  `src/sort.d`
    A sorting routine.
`src/spvwtabf.d`
  The table of built-in special operators and functions.
`src/spvwtabs.d`
  The table of all `SYMBOL`s accessed by C code.
`src/spvwtabo.d`
  The table of miscellaneous objects accessed by C code.
`src/eval.d`

  Evaluator (form interpreter) and bytecode interpreter.

  `src/bytecode.d`
    List of bytecodes.
  `src/lightning.c`
    Just-in-time compiler using GNU lightning.
`src/control.d`
  Special operator interpreter.
`src/pathname.d`
  Pathnames, file- and directory-related functions.
`src/stream.d`
  `STREAM`s of all kinds: `FILE-STREAM`s, terminal streams, `STRING-STREAM`s etc.
`src/socket.d`
  Opening sockets for `TCP`/`IP` and CLX.
`src/io.d`
  The lisp reader (parser) and printer (including pretty printer).
`src/array.d`
  Functions dealing with `ARRAY`s and `VECTOR`s.
`src/hashtabl.d`
  Functions dealing with `HASH-TABLE`s.
`src/list.d`
  Functions dealing with `LIST`s.
`src/package.d`
  Functions dealing with `PACKAGE`s.
`src/record.d`
  Functions dealing with records (structures, closures, etc.)
`src/sequence.d`
  The generic `SEQUENCE` functions.
`src/funarg.d`
  Functional arguments, like `:TEST` and `:KEY`.
`src/charstrg.d`
  Functions dealing with `CHARACTER`s and `STRING`s.
`src/debug.d`
  The debugger and the read-eval-print loop.
`src/error.d`

  `ERROR` handling and `SIGNAL`ing.

  `src/errunix.d`
    UNIX-specific error messages.
  `src/errwin32.d`
    Win32-specific error messages.
`src/misc.d`
  Miscellaneous functions.
`src/time.d`
  Timing functions.
`src/predtype.d`
  Predicates, type tests.
`src/symbol.d`
  Functions dealing with `SYMBOL`s.
`src/unixaux.d`
  Auxiliary functions (UNIX version only).
`src/win32aux.d`
  Auxiliary functions (Win32 version only).
`src/foreign.d`
  “FFI” implementation.
`src/lisparit.d`
  Functions dealing with numbers (arithmetic), see Section 34.3.1.3, “Number system (arithmetic)”.
`src/noreadline.d`
  Dummy plug-in for the GNU readline library.
`src/zthread.d`
  MT implementation.

#### 34.3.1.3. Number system (arithmetic)

`src/lisparit.d`
  initialization, input/output of numbers, lisp functions
`src/aridecl.d`
  declarations
`src/arilev0.d`
  arithmetic at the machine level
`src/arilev1.d`
  digit sequences
`src/arilev1c.d`
  operations on digit sequences, written in C
`src/arilev1i.d`
  operations on digit sequences, as inline functions
`src/arilev1e.d`
  operations on digit sequences, bindings to external routines
`src/intelem.d`
  `INTEGER`s: elementary operations
`src/intlog.d`
  `INTEGER`s: logical connectives
`src/intplus.d`
  `INTEGER`s: addition and subtraction
`src/intcomp.d`
  `INTEGER`s: comparison
`src/intbyte.d`
  `INTEGER`s: byte operations `LDB`, `DPB`
`src/intmal.d`
  `INTEGER`s: multiplication
`src/intdiv.d`
  `INTEGER`s: division
`src/intgcd.d`
  `INTEGER`s: `GCD` and `LCM`
`src/int2adic.d`
  `INTEGER`s: operations on 2-adic integers
`src/intsqrt.d`
  `INTEGER`s: square root, n-th root
`src/intprint.d`
  subroutines for `INTEGER` output
`src/intread.d`
  subroutines for `INTEGER` input
`src/rational.d`
  rational numbers (`RATIO`s)
`src/sfloat.d`
  elementary operations for `SHORT-FLOAT`s
`src/ffloat.d`
  elementary operations for `SINGLE-FLOAT`s
`src/dfloat.d`
  elementary operations for `DOUBLE-FLOAT`s
`src/lfloat.d`
  elementary operations for `LONG-FLOAT`s
`src/flo_konv.d`
  conversions between `FLOAT`s
`src/flo_rest.d`
  general `FLOAT` operations
`src/realelem.d`
  elementary functions for `REAL` numbers
`src/realrand.d`
  random numbers
`src/realtran.d`
  transcendental functions for `REAL` numbers
`src/compelem.d`
  elementary functions for `COMPLEX` numbers
`src/comptran.d`
  transcendental functions for `COMPLEX` numbers

##### 34.3.1.3.1. External routines for the arithmetic system, written in assembly language

`src/ari_asm_sparc.d`
  written in SPARC assembler
`src/ari_asm_sparc64.d`
  written in 64-bit SPARC assembler
`src/ari_asm_i386.d`
  written in i386/i486 assembler
`src/ari_asm_mips.d`
  written in MIPS assembler
`src/ari_asm_mips64.d`
  written in 64-bit MIPS assembler
`src/ari_asm_hppa.d`
  written in HPPA-1.0 assembler
`src/ari_asm_arm.d`
  written in ARM assembler

#### 34.3.1.4. External routines for accessing the stack, written in assembly language

`src/sp_asm_m68k.d`
  written in 68000 assembler, MIT syntax
`src/sp_asm_sparc.d`
  written in SPARC assembler
`src/sp_asm_sparc64.d`
  written in 64-bit SPARC assembler
`src/sp_asm_i386.d`
  written in i386/i486 assembler
`src/sp_asm_mips.d`
  written in MIPS assembler

### 34.3.2. Other assembly language stuff

`src/asm-i386.sh`
  converts i386 assembler from Linux/i386 format (with MIT syntax) to a macro syntax
`src/asm-i386.h`
  expands i386 assembler in macro syntax to either MIT or Intel syntax
`src/noexecstack.h`
  Ensures that a hand-written assembly-language file does not force an executable stack in the process that executes. This is needed because the GNU binutils developers, when adding some security feature in 2005, favoured backward compatibility of already built object files, at the detriment of programmers who write assembly-language. For more details, see the notes in GNU libffcall.

### 34.3.3. Lisp source files

`src/init.lisp`
  the first file to be loaded during bootstrapping, loads everything else
`src/defseq.lisp`
  defines the usual sequence types for the generic sequence functions
`src/backquote.lisp`
  implements the backquote read macro
`src/defmacro.lisp`
  implements `DEFMACRO`
`src/macros1.lisp`
  the most important macros
`src/macros2.lisp`
  some other macros
`src/defs1.lisp`
  miscellaneous definitions
`src/timezone.lisp`
  site-dependent definition of time zone, except for UNIX and Win32.
`src/places.lisp`
  macros using places, definitions of most standard and extensiion places
`src/floatprint.lisp`
  defines `SYS::WRITE-FLOAT-DECIMAL` for printing floating point numbers in base 10
`src/type.lisp`
  functions working with type specifiers: `TYPEP`, `SUBTYPEP`
`src/defstruct.lisp`
  implements the macro `DEFSTRUCT`
`src/format.lisp`
  implements the function `FORMAT`
`src/room.lisp`
  implements the function `ROOM` (see also Section 25.3.1, “Function `ROOM`”)
`src/savemem.lisp`
  see Section 31.2, “Saving an Image”
`src/xcharin.lisp` (optional)
  implements extended character input for `EXT:WITH-KEYBOARD`
`src/keyboard.lisp` (optional)
  implements the macro `EXT:WITH-KEYBOARD`
`src/runprog.lisp`
  implements the functions `EXT:RUN-PROGRAM`, `EXT:RUN-SHELL-COMMAND` etc.
`src/query.lisp`
  implements the functions `Y-OR-N-P` and `YES-OR-NO-P`
`src/reploop.lisp`
  support for the debugger and the read-eval-print loop
`src/dribble.lisp`
  implements the functions `DRIBBLE` and `EXT:DRIBBLE-STREAM`
`src/complete.lisp`
  implements completion, see Section 21.2, “Terminal interaction”.
`src/describe.lisp`
  implements functions `DESCRIBE`, `APROPOS`, `APROPOS-LIST`
`src/trace.lisp`
  tracer
`src/macros3.lisp` (optional)
  macros `EXT:LETF`, `EXT:LETF*`, `EXT:ETHE`, `EXT:WITH-COLLECT`, function `EXT:COMPILED-FILE-P`.
`build/config.lisp`

  site-dependent configuration, a user-modified copy of one of the following:

  `src/cfgunix.lisp`
    for UNIX
  `src/cfgwin32.lisp`
    for the Win32

  See Section 31.12, “Customizing CLISP behavior”.

`src/compiler.lisp`
  compiles Lisp code to bytecode
`src/functions.lisp`
  `FUNCTION-LAMBDA-EXPRESSION` et al
`src/disassem.lisp`
  the function `DISASSEMBLE`
`src/defs2.lisp`
  miscellaneous [ANSI CL standard] definitions
`src/loop.lisp`
  implements the [ANSI CL standard]-compatible `LOOP` macro
`src/clos.lisp`

  loads the various parts of the CLOS:

  `src/clos-package.lisp`
    declares the imports and exports of the “CLOS” package
  `src/clos-macros.lisp`
    defines some internal macros used by the CLOS implementation
  `src/clos-class0.lisp`
    defines the `class-version` structure
  `src/clos-metaobject1.lisp`
    defines the `CLOS:METAOBJECT` class
  `src/clos-slotdef1.lisp`
    defines the `CLOS:SLOT-DEFINITION` class and its subclasses
  `src/clos-slotdef2.lisp`
    defines `INITIALIZE-INSTANCE` methods for `CLOS:SLOT-DEFINITION` and its subclasses
  `src/clos-slotdef3.lisp`
    defines the generic functions that can be used on `CLOS:SLOT-DEFINITION` objects
  `src/clos-stablehash1.lisp`
    defines the `EXT:STANDARD-STABLEHASH` class
  `src/clos-stablehash2.lisp`
    defines `INITIALIZE-INSTANCE` methods for `EXT:STANDARD-STABLEHASH`
  `src/clos-specializer1.lisp`
    defines the `CLOS:SPECIALIZER` class and its subclasses
  `src/clos-specializer2.lisp`
    defines `INITIALIZE-INSTANCE` methods for `CLOS:SPECIALIZER` and its subclasses
  `src/clos-specializer3.lisp`
    defines the generic functions that can be used on `CLOS:SPECIALIZER` objects
  `src/clos-class1.lisp`
    defines the `potential-class` class and its subclasses
  `src/clos-class2.lisp`
    implements the mapping from class names to classes
  `src/clos-class3.lisp`
    implements the `DEFCLASS` macro, class definition and class redefinition
  `src/clos-class4.lisp`
    defines `INITIALIZE-INSTANCE` methods for `potential-class` and its subclasses
  `src/clos-class5.lisp`
    implements the special logic of `MAKE-INSTANCE`, `INITIALIZE-INSTANCE` etc.
  `src/clos-class6.lisp`
    defines the generic functions that can be used on `potential-class` objects
  `src/clos-method1.lisp`
    defines the `METHOD` class and its subclasses
  `src/clos-method2.lisp`
    implements the bulk of `DEFMETHOD`
  `src/clos-method3.lisp`
    defines the generic functions that can be used on `METHOD` objects
  `src/clos-method4.lisp`
    makes generic functions on `STANDARD-METHOD` objects extensible
  `src/clos-methcomb1.lisp`
    defines the `METHOD-COMBINATION` class
  `src/clos-methcomb2.lisp`
    implements method combination (part 2 of generic function dispatch and execution) and the `DEFINE-METHOD-COMBINATION` macro
  `src/clos-methcomb3.lisp`
    defines `INITIALIZE-INSTANCE` methods for `METHOD-COMBINATION`
  `src/clos-methcomb4.lisp`
    makes generic functions on `METHOD-COMBINATION` objects extensible
  `src/clos-genfun1.lisp`
    defines the `GENERIC-FUNCTION` class and its metaclass, superclass and subclasses
  `src/clos-genfun2a.lisp`
    implements part 1 of generic function dispatch and execution
  `src/clos-genfun2b.lisp`
    implements part 3 of generic function dispatch and execution
  `src/clos-genfun3.lisp`
    implements creation of generic function objects, `DEFMETHOD`, `DEFGENERIC`
  `src/clos-genfun4.lisp`
    defines `INITIALIZE-INSTANCE` methods for `GENERIC-FUNCTION` and its subclasses
  `src/clos-genfun5.lisp`
    makes generic functions on `GENERIC-FUNCTION` objects extensible
  `src/clos-slots1.lisp`
    implements low-level slot access, `WITH-SLOTS`, `WITH-ACCESSORS`
  `src/clos-slots2.lisp`
    defines the generic functions that deal with slot access
  `src/clos-dependent.lisp`
    implements notification from metaobjects to dependent objects
  `src/clos-print.lisp`
    implements the function `PRINT-OBJECT`
  `src/clos-custom.lisp`
    provides user customization of the CLOS
`src/gray.lisp`
  implements STREAM-DEFINITION-BY-USER:GENERIC-FUNCTIONS
`src/fill-out.lisp`
  implements `EXT:FILL-STREAM`
`src/disassem.lisp`
  implements `DISASSEMBLE`
`src/condition.lisp`
  implements the Common Lisp Condition System (CLCS)
`src/gstream.lisp` (optional)
  generic stream default methods, see Section 31.6, “Generic streams”
`src/foreign1.lisp`
  “FFI” implementation.
`src/screen.lisp`
  the screen access package, see Section 32.1, “Random Screen Access”
`src/edit.lisp` (optional)
  the screen editor (`ED`), `EXT:UNCOMPILE`
`src/inspect.lisp`
  implements `INSPECT` (tty and HTTP frontends)
`src/clhs.lisp`
  implements `EXT:OPEN-HTTP`, `EXT:BROWSE-URL`
`src/exporting.lisp`
  Macros that export their definienda, see Section 32.2.7.3, “Exporting”.
`src/threads.lisp`
  MT interface
`src/german.lisp`
`src/french.lisp`
`src/spanish.lisp`
`src/russian.lisp`
`src/danish.lisp`
`src/dutch.lisp`
  i18n user messages

### 34.3.4. External Modules

`modules/`
  individual external module sources

### 34.3.5. Documentation

`src/NEWS`
  the list of the user-visible changes
`src/_README`

  master for the distribution's README

  `src/_README.en`
  `src/_README.de`
  `src/_README.es`
    translations of `src/_README`
`doc/clisp.xml.in`
  DocBook/XML sources for the CLISP manual page
``build-dir`/clisp.1`
  the platform-specific man manual page, generated from `doc/clisp.xml.in` at build time
``build-dir`/clisp.html`
  the platform-specific HTML manual page, generated from `doc/clisp.xml.in` at build time
`doc/impnotes.xml.in`

  the master DocBook/XML file for these implementation notes; includes the following files

  `doc/cl-ent.xml`
    CLISP-independent general Common Lisp-related entities
  `doc/clhs-ent.xml`
    generated list of [Common Lisp HyperSpec] entities
  `doc/impent.xml`
    CLISP-specific entities
  `doc/unix-ent.xml`
    UNIX-related entities
  `doc/mop-ent.xml`
    Meta-Object Protocol-related entities
  `doc/impbody.xml`
    most of Part I, “Chapters or the Common Lisp HyperSpec”
  `doc/impissue.xml`
    Chapter 28, X3J13 Issue Index [CLHS-ic]
  `doc/gray.xml`
    Chapter 30, Gray streams
  `doc/mop.xml`
    Chapter 29, Meta-Object Protocol
  `doc/impext.xml`
    Chapter 31, Platform Independent Extensions and Chapter 32, Platform Specific Extensions
  `doc/impbyte.xml`
    this Part IV, “Internals of the CLISP Implementation”
  `doc/faq.xml`
    Appendix A, Frequently Asked Questions (With Answers) about CLISP
  `modules/**/*.xml`
    individual external module documentation
  `doc/Symbol-Table.text`
    the mapping between lisp symbols and element IDs in these notes (see `DESCRIBE`), installed in `data/` under `CUSTOM:*LIB-DIRECTORY*`.
`doc/impnotes.html`
  these HTML implementation notes, generated from `doc/impnotes.xml.in` at release time

### 34.3.6. Internationalization

These files are usually updated a couple of weeks before a CLISP release using make -f Makefile.devel tp-mail, see also Section 34.3.8, “Externally maintained files”.

We use the Translation project and the above command sends the updated files to the translators.

`src/po/*.pot`
  list of translatable messages (“portable object template”)
`src/po/*.po`
  translated messages (“portable objects”)
`src/po/*.gmo`
  translated messages (“GNU format message objects”)

### 34.3.7. Automatic configuration on UNIX and MinGW

`configure`
  the main configuration script
`version.sh`
  specifies the current CLISP version
`src/configure.in`
  lists features to be checked
`src/m4/`

  a repertoire of features. Use with GNU autoconf 2.62

  `src/m4/clisp.m4`

    This file defines the macro `CL_CLISP` which takes two optional parameters:

    features-list
      The list of CLISP features to check. E.g., passing `[foo bar]` results in `cl_cv_clisp_FOO` and `cl_cv_clisp_BAR` being defined to yes or no, depending on the value of `*FEATURES*`, i.e., on the return value of `(`READ-FROM-STRING` "#+FOO \"yes\" #-FOO \"no\"")`.
    required

      Determines whether configure should fail if CLISP or one of the requested features is missing.

      Should be true (the default) or false.

    Calling this macro causes the generated configure to accept the option `--with-clisp="clisp command line"` which allows one to use a specific CLISP installation instead of clisp in `PATH`.

    In addition to the aforementioned per-feature variables, this macro defines the follwing variables:

    `cl_cv_clisp_version`
      The return value of `LISP-IMPLEMENTATION-VERSION`.
    `cl_cv_clisp_libdir`
      The `NAMESTRING` of `CUSTOM:*LIB-DIRECTORY*`.
    `cl_cv_clisp_linkset`
      The directory of the current linking set.

    It also substitues the following variables:

    `CLISP_LINKKIT`
    `CLISP_FILES`
    `CLISP_LIBS`
    `CLISP_CFLAGS`
    `CLISP_CPPFLAGS`

    (taken from `$cl_cv_clisp_linkset/makevars`) and `CLISP` (the CLISP command line).

    This file is installed in `/usr/share/aclocal` by make install.

`src/configure`
  configuration script, generated from `src/configure.in`
`src/intparam.c`
  figures out some machine parameters (word size, endianness etc.)
`src/floatparam.c`
  figures out some floating point arithmetics parameters (rounding, epsilons etc.)
`src/config.h.in`
  header file master, generated from `src/configure.in`. ``build-dir`/config.h` contains the values of the features discovered by `src/configure`.
`src/makemake.in`
  makefile construction script master
`src/_clisp.c`
  master for the distribution's driver program
`src/_distmakefile`
  master for the distribution's Makefile

### 34.3.8. Externally maintained files

The externally maintained files are usually updated a couple of weeks before a CLISP release using make -f Makefile.devel pre-release, see also Section 34.3.6, “Internationalization”.

`src/gllib/`
`src/glm4/`
  C and GNU autoconf files from GNU Portability Library; updated using make -f Makefile.devel gnulib-imported at top level.
`src/build-aux/`
  various shell scripts, updated using make -f Makefile.devel build-aux-update at top level.

## Chapter 35. Overview of CLISP's Garbage Collection

Abstract

These are internals, which are of interest only to the CLISP developers. If you do not read clisp-devel, this chapter is probably not for you.

## 35.1. Introduction

Knowing that most `malloc` implementations are buggy and/or slow, and because CLISP needs to perform garbage-collection, CLISP has its own memory management subsystem in files `src/spvw*.d`, see Section 34.3.1.2, “Internal C Modules”.

## 35.2. Lisp objects in CLISP

Three kinds of storage are distinguished:

1. CLISP data (the “heap”), i.e. storage which contains CLISP objects and is managed by the garbage-collector.
2. CLISP stack (called `STACK`), contains CLISP objects visible to the garbage-collector
3. C data (including program text, data, `malloc`ed memory)

A CLISP object is one word, containing a tag (partial type information) and either immediate data or a pointer to storage. Pointers to C data have tag = `machine_type` = 0, pointers to CLISP stack have tag = `system_type`, most other pointers point to CLISP data.

Immediate objects

32-bit CPU

  `FIXNUM`
  `SHORT-FLOAT`
  `CHARACTER`

64-bit CPU

  In addition to the above,

  `SINGLE-FLOAT` (with `TYPECODES`)

Let us turn to those CLISP objects that consume regular CLISP memory. Every CLISP object has a size which is determined when the object is allocated (using one of the `allocate_*()` routines). The size can be computed from the type tag and - if necessary - the length field of the object's header. The length field always contains the number of elements of the object. The number of bytes is given by the function `objsize()`.

CLISP objects which contain exactly 2 CLISP objects (i.e. `CONS`es, `COMPLEX` numbers, `RATIO`s) are stored in a separate area and occupy 2 words each. All other CLISP objects have “varying” length (more precisely, not a fixed length) and include a word for garbage-collection purposes at their beginning.

The garbage collector is invoked every now and then by `allocate_*()` calls according to certain heuristics. It marks all objects which are “alive” (may be reached from the “roots”), compacts these objects and unmarks them. Non-live objects are lost; their storage is reclaimed.

2-pointer objects are compacted by a simple hole-filling algorithm: fill the left-most object into the right-most hole, and so on, until the objects are contiguous at the right and the hole is contiguous at the left.

Variable-length objects are compacted by sliding them down (their address decreases).

## 35.3. Object Pointer Representations

CLISP implements two ways of representing object pointers. (An object pointer, C type object, contains a pointer to the memory location of the object, or - for immediate object - all bits of the object itself.) Both of them have some things in common:

- There is a distinction between immediate objects (`CHARACTER`s, `FIXNUM`s, `SHORT-FLOAT`s, etc) and heap allocated objects.
- All object pointers are typed, i.e. contain a few bits of information about the type of the pointed-to object. At a minimum, these bits must allow to distinguish immediate and heap-allocated objects.
- Not all of the type information is contained in the object pointer. For example, CLOS objects can change their type when `CHANGE-CLASS` is called. To avoid scanning all the heap for references when this happens, the class information is stored in the heap allocated object, not in the object pointer.

The `HEAPCODES` object representation has a minimum of type bits in the object pointer, namely, 2 bits. They allow to distinguish immediate objects (which have some more type bits), `CONS`es (which have no type bits in the heap, since they occupy just two words in the heap, with no header), other heap objects (many, from `SIMPLE-VECTOR`s to `FFI:FOREIGN-POINTER`s), and Subrs. Most object types are distinguished by looking a the `rectype` field in the header of the heap object.

The `TYPECODES` object representation has about two dozen of types encoded in 6 or 7 bits in the object pointer. Typically these are the upper 8 bits of a word (on a 32-bit machine) or the upper 16 bits or 32 bits of a word (on a 64-bit machine). The particular values of the typecodes allow many common operations to be performed with a single bit test (e.g. `CONSP` and `MINUSP` for a `REAL` are bit tests) or range check. However, the `rectype` field still exists for many types, because there are many built-in types which do not need a particularly fast type test.

Which object representation is chosen is decided at build time depending on the available preprocessor definitions. You can define `TYPECODES` or `HEAPCODES` to force one or the other.

One might expect that `TYPECODES` is faster than `HEAPCODES` because it does not need to make as many memory accesses. This effect is, however, hardly measurable in practice (certainly not more than 5% faster). Apparently because, first, the situations where the type of an object is requested but then the object is not looked into are rare. It is much more common to look into an object, regardless of its type. Second, due to the existence of data caches in the CPU, accessing a heap location twice, once for the type test and then immediately afterwards for the data, is not significantly slower than just accessing the data.

`TYPECODES` is problematic on 32-bit machines, when you want to use more than 16 MB of memory, because the type bits (at bit 31..24) interfere with the bits of a heap address. For this reason, `HEAPCODES` is the default on 32-bit platforms.

`HEAPCODES` is problematic on platforms whose object alignment is less than 4. This affects only the mc680x0 CPU; however, here the alignment can usually be guaranteed through some gcc options.

## 35.4. Memory Models

There are 6 memory models. Which one is used, depends on the operating system and is determined at build time.

Memory Models

SPVW_MIXED_BLOCKS_OPPOSITE

  The heap consists of one block of fixed length (allocated at startup). The variable-length objects are allocated from the left, the 2-pointer objects are allocated from the right. There is a hole between them. When the hole shrinks to 0, garbage-collect is invoked. garbage-collect slides the variable-length objects to the left and concentrates the 2-pointer objects at the right end of the block again. When no more room is available, some reserve area beyond the right end of the block is halved, and the 2-pointer objects are moved to the right accordingly.

  Advantages and Disadvantages

  (+) | Simple management.
  (+) | No fragmentation at all.
  (-) | The total heap size is limited.

SPVW_MIXED_BLOCKS_OPPOSITE & TRIVIALMAP_MEMORY

  The heap consists of two big blocks, one for variable-length objects and one for 2-pointer objects. The former one has a hole to the right and is extensible to the right, the latter one has a hole to the left and is extensible to the left. Similar to the previous model, except that the hole is unmapped.

  Advantages and Disadvantages

  (+) | Total heap size grows depending on the application's needs.
  (+) | No fragmentation at all.
  (*) | Works only when SINGLEMAP_MEMORY is possible as well.

SPVW_MIXED_BLOCKS_STAGGERED & TRIVIALMAP_MEMORY

  The heap consists of two big blocks, one for variable-length objects and one for 2-pointer objects. Both have a hole to the right, but are extensible to the right.

  Advantages and Disadvantages

  (+) | Total heap size grows depending on the application's needs.
  (+) | No fragmentation at all.
  (*) | Works only when SINGLEMAP_MEMORY is possible as well.

SPVW_MIXED_PAGES

  The heap consists of many small pages (usually around 8 KB). There are two kinds of pages: one for 2-pointer objects, one for variable-length objects. The set of all pages of a fixed kind is called a "Heap". Each page has its hole (free space) at its end. For every heap, the pages are kept sorted according to the size of their hole, using AVL trees. The garbage-collection is invoked when the used space has grown by 25% since the last GC; until that point new pages are allocated from the OS. The GC compacts the data in each page separately: data is moved to the left. Emptied pages are given back to the OS. If the holes then make up more than 25% of the occupied storage, a second GC turn moves objects across pages, from nearly empty ones to nearly full ones, with the aim to free as many pages as possible.

  Advantages and Disadvantages

  (-) | Every allocation requires AVL tree operations, thus slower
  (+) | Total heap size grows depending on the application's needs.
  (+) | Works on operating systems which do not provide large contiguous areas.

SPVW_PURE_PAGES

  Just like SPVW_MIXED_PAGES, except that every page contains data of only a single type tag, i.e. there is a Heap for every type tag.

  Advantages and Disadvantages

  (-) | Every allocation requires AVL tree operations, thus slower
  (+) | Total heap size grows depending on the application's needs.
  (+) | Works on operating systems which do not provide large contiguous areas.
  (-) | More fragmentation because objects of different type never fit into the same page.

SPVW_PURE_BLOCKS

  There is a big block of storage for each type tag. Each of these blocks has its data to the left and the hole to the right, but these blocks are extensible to the right (because there is enough room between them). A garbage-collection is triggered when the allocation amount since the last GC reaches 50% of the amount of used space at the last GC, but at least 512 KB. The garbage-collection cleans up each block separately: data is moved left.

  Advantages and Disadvantages

  (+) | Total heap size grows depending on the application's needs.
  (+) | No 16 MB total size limit.
  (*) | Works only in combination with SINGLEMAP_MEMORY.

In page based memory models, an object larger than a page is the only object carried by its pages. There are no small objects in pages belonging to a big object.

The following combinations of memory model and `mmap` tricks are possible (the number indicates the order in which the respective models have been developed):

Table 35.1. Memory models with `TYPECODES`

| A | B | C | D
--- | --- | --- | --- | ---
SPVW_MIXED_BLOCKS_OPPOSITE | 1 | 9 |  | 8
SPVW_MIXED_BLOCKS_STAGGERED |  | 6 |  | 7
SPVW_PURE_BLOCKS |  |  | 4 | 5
SPVW_MIXED_PAGES | 2 |  |  |
SPVW_PURE_PAGES | 3 |  |  |

Table 35.2. Memory models with `HEAPCODES`

| A | B | D
--- | --- | --- | ---
SPVW_MIXED_BLOCKS_OPPOSITE | * | * | *
SPVW_MIXED_BLOCKS_STAGGERED |  | * | *
SPVW_MIXED_PAGES | * |  |

Legend to Table 35.1, “Memory models with `TYPECODES`” and Table 35.2, “Memory models with `HEAPCODES`”

1. no MAP_MEMORY
2. TRIVIALMAP_MEMORY
3. SINGLEMAP_MEMORY
4. GENERATIONAL_GC

## 35.5. The burden of garbage-collection upon the rest of CLISP

### 35.5.1. Lisp object invalidation

Every subroutine marked with “can trigger GC” or `maygc` may invoke garbage-collection. The garbage-collector moves all the CLISP non-immediate objects and updates the pointers. But the garbage-collector looks only at the `STACK` and not in the C variables. (Anything else would not be portable.) Therefore at every "unsafe" point, i.e. every call to such a subroutine, all the C variables of type object MUST BE ASSUMED TO BECOME GARBAGE. (Except for objects that are known to be unmovable, e.g. immediate objects or Subrs.) Pointers inside CLISP data (e.g. to the characters of a `STRING` or to the elements of a `SIMPLE-VECTOR`) become INVALID as well.

### 35.5.2. Managing Lisp objects in C

The workaround is usually to allocate all the needed CLISP data first and do the rest of the computation with C variables, without calling unsafe routines, and without worrying about garbage-collection.

Alternatively, you can save a lisp object on the `STACK` using macros `pushSTACK()` and `popSTACK()`.

### Warning

One should not mix these macros with functions which modify `STACK` in one statement because C may execute different parts of the statement out of order. E.g.,

    pushSTACK(listof(4));

is illegal while

    pushSTACK(STACK_0);

is legal.

### 35.5.3. Run-time GC-safety checks

Run-time GC-safety checking is available when you build CLISP with a C++ compiler, e.g.:

    $ ./configure 'CC=g++' --with-debug build-g-gxx

When built like this, CLISP will `abort` when you reference GC-unsafe data after an allocation (which could have triggered a garbage-collection), and gdb will pinpoint the trouble spot.

Specifically, when CLISP is configured as above, there is a global integer variable `alloccount` and the object structure contains an integer `allocstamp` slot. If these two integers are not the same, the object is invalid. By playing with gdb, you should be able to figure out the precise spot where an allocation increments `alloccount` after the object has been retrieved from a GC-visible location.

### 35.5.4. Memory protection

Generational garbage-collector uses memory protection, so when passing pointers into the lisp heap to C functions, you may encounter errors (`errno`=`EFAULT`) unless you call `handle_fault_range(protection,region_start,region_end)` on the appropriate memory region. See files

`src/unixaux.d`
`src/win32aux.d`
`modules/syscalls/calls.c`
`modules/rawsock/rawsock.c`

for examples.

## 35.6. Foreign Pointers

Pointers to C functions and to `malloc`ed data can be hidden in CLISP objects of type machine_type; garbage-collect will not modify its value. But one should not dare to assume that a C stack pointer or the address of a C function in a shared library satisfies the same requirements.

If another pointer is to be viewed as a CLISP object, it is best to box it, e.g. in a `SIMPLE-BIT-VECTOR` or in an Fpointer (using `allocate_fpointer()`.)

## 35.7. Forcing or inhibiting Garbage Collections

Here are some tips to debug garbage-collection-related problems.

It is possible to force garbage-collections to occur at specific points, by inserting calls to `EXT:GC` in the code.

It is also possible to make garbage-collections more frequent overall, by use of the command-line option `-nextgc-factor`. This option specifies a factor that gets applied to the amount of space that can be consumed before the next garbage-collection is triggered. If you specify a factor smaller than 1, the frequency of garbage-collections is increased. For example, ``-nextgc-factor` 0.001` reduces the "Bytes available until next GC" value displayed by the `ROOM` function by a factor of 1000, and thus makes garbage-collections 1000 times more frequent.

It is equally possible to make garbage-collections less frequent. To this effect, you pass to `-nextgc-factor` a value larger than 1. For example, ``-nextgc-factor` 1e9` multiplies the "Bytes available until next GC" value displayed by the `ROOM` function with a factor of 1000000000, and thus effectively inhibits garbage-collections entirely.

## 35.8. Garbage Collection and Multithreading

While the garbage-collection is executing, all other threads must stop. CLISP has a copying garbage-collector, so anything else would require a write barrier during the scan phase and a read barrier during the move phase.

Pinned heap objects. Heap objects may be pinned - they will not move during garbage-collection. Used when execution is blocked in a foreign/system call and a pointer into the heap is passed to non-lisp land. The garbage-collector tries to minimize the holes in the heap introduced by the pinning process. See also the note about system calls in Section 32.2.7.2, “clisp.h”.

Safe points. The threads may be stopped only at certain safe points. Currently implemented safe points are:

1. Any heap allocation (actually before the allocation itself).
2. Possibly blocking system call.
3. Some places that may introduce infinite non-consing loops.

Basically any thread that conses or can block in a system call will not stop the garbage-collection from executing. There are still places where infinite non-consing loop without safe point may be reached (TODO: find and fix)

## Chapter 36. Extending CLISP Core

You are urged to use External Modules instead of adding built-in functions.

### Note

CLISP comes with an “FFI” which allows you to access C libraries in an easy way (including creating `FFI:FOREIGN-FUNCTION`s dynamically).

## 36.1. Adding a built-in function

In the rare cases when you really need to modify CLISP internals and add a truly built-in function, you should read the CLISP sources for inspiration and enlightenment, choose a file where your brand-new built-in function should go to, and then ...

- add the `LISPFUN` form and the implementation there
- add the `LISPFUN` header to file `subr.d`
- declare the function name in file `constsym.d` in the appropriate package (probably “EXT”, if there is no specific package)
- if your function accepts keyword arguments, then you must make sure that the keyword symbols are declared in `constsym.d`
- see the example in Section 32.2.7.1, “Modprep” for argument passing and returning values
- export your function name from the appropriate package in file `init.lisp`
- when you are done, you should run make check-sources in your build directory: this will check that the definitions (source files) and the declarations (`subr.d` and `fsubr.d`) are in sync.

### Warning

Be very careful with the GC-unsafe functions! Always remember about GC-safety!

These instructions are intentionally terse - you are encouraged to use modules and/or “FFI” instead of adding built-ins directly.

## 36.2. Adding a built-in variable

If you must be able to access the Lisp variable in the C code, follow these steps:

- declare the variable name in `constsym.d` in the appropriate package (probably “CUSTOM”, if there is no specific package);
- add a `define_variable()` call in function `init_symbol_values()` in file `spvw.d`
- export your variable name from the appropriate package in file `init.lisp`

## 36.3. Recompilation

Any change that forces make to remake `lisp.run`, will force recompilation of all `#P".lisp"` files and re-dumping of `lispinit.mem`, which may be time-consuming. This is not always necessary, depending on what kind of change you introduced.

On the other hand, if you change any of the following files:

`constobj.d`
`constsym.d`
`fsubr.d`
`subr.d`

your `lispinit.mem` will have to be re-dumped.

### Warning

If you change the signature of any system function mentioned in the `FUNTAB`* arrays in file `eval.d`, all the `#P".fas"` files will become obsolete and will need to be recompiled. You will need to add a note to that effect to the `src/NEWS` file and augment the object `version` in file `constobj.d`. Please try to avoid this as much as possible.

## Chapter 37. The CLISP bytecode specification

## 37.1. Introduction

The CLISP compiler compiles Common Lisp programs into instruction codes for a virtual processor. This bytecode is optimized for saving space in the most common cases of Common Lisp programs. The main advantages/drawbacks of this approach, compared to native code compilation, are:

- Bytecode compiled programs are a lot smaller than when compiled to native code. This results in better use of CPU caches, and in less virtual memory paging. Users perceive this as good responsiveness.
- Maximum execution speed (throughput in tight loops) is limited.
- Since no bytecode instructions are provided for “unsafe” operations (like unchecked array accesses, or “fast” `CAR`/`CDR`), programs run with all safety checks enabled even when compiled.
- Execution speed of a program can easily be understood by looking at the output of the `DISASSEMBLE` function. A rule of thumb is that every elementary instruction costs 1 time unit, whereas a function call costs 3 to 4 time units.
- Needing to do no type inference, the compiler is pretty straightforward and fast. As a consequence, the definition of CLOS generic functions, which needs to compile small pieces of generated code, is not perceived to be slow.
- The compiler is independent from the hardware CPU. Different back-ends, one for each hardware CPU, are not needed. As a consequence, the compiler is fairly small (and would have been easily maintainable if it were written in a less kludgey way...), and it is impossible for the compiler writer to introduce CPU dependent bugs.

## 37.2. The virtual machine

The bytecode can be thought of as being interpreted by a virtual processor. The engine which interprets the bytecode (the “implementation of the virtual machine”) is either a C function (`interpret_bytecode` in `eval.d`), or a just-in-time compiler which translates a function's bytecode into hardware CPU instructions the first time said function is called, see Section 3.2.1.1, “Just-In-Time Native Compilation”.

The virtual machine is a stack machine with two stacks:

`STACK`
  a stack for CLISP objects and frames (“Lisp stack”).
`SP`
  a stack for other data and pointers (“Program stack”).

This two-stack architecture permits to save an unlimited number of CLISP objects on the `STACK` (needed for handling of Common Lisp multiple values), without consing[3]. Also, in a world with a compacting no-ambiguous-roots garbage collector, `STACK` must only hold CLISP objects, and `SP` can hold all the other data belonging to a frame, which would not fit into `STACK` without tagging/untagging overhead.

The scope of `STACK` and `SP` is only valid for a given function invocation. Whereas the amount of `STACK` space needed for executing a function (excluding other function calls) is unlimited, the amount of `SP` space needed is known a priori, at compile time. When a function is called, no relation is specified between the caller's `STACK` and the callee's `STACK`, and between the caller's `SP` and the callee's `SP`. The bytecode is designed so that outgoing arguments on the caller's `STACK` can be shared by the caller's incoming arguments area (on the callee's `STACK`), but a virtual machine implementation may also copy outgoing arguments to incoming arguments instead of sharing them.

The virtual machine has a special data structure, `values`, containing the “top of stack”, specially adapted to Common Lisp multiple values:

`mv_count`
  an unsigned integer.
`value1`
  the primary value, a CLISP object. If `mv_count` = 0, this is `NIL`.
`mv_space`
  all values except the first one, an array of CLISP objects.

The contents of `values` is short-lived. It does not survive a function call, not even a garbage-collection.

The interpretation of some bytecode instructions depends on a constant, `jmpbufsize`. This is a CPU-dependent number, the value of `SYSTEM::*JMPBUF-SIZE*`. In C, it is defined as `ceiling(sizeof(jmp_buf),sizeof(void*))`.

## 37.3. The structure of compiled functions

A compiled function consists of two objects: The function itself, containing the references to all CLISP objects needed for the bytecode, and a byte vector containing only immediate data, including the bytecode proper.

Typically, the byte vector is about twice as large as the function vector. The separation thus helps the garbage collector (since the byte vector does not need to be scanned for pointers).

A function looks like this (cf. the C type Cclosure):

name
  This is the name of the function, normally a symbol or a list of the form `(`SETF` `symbol`)`. It is used for printing the function and for error messages. This field is immutable.
`codevec`
  This is the byte-code vector, a `(`VECTOR` (`UNSIGNED-BYTE` 8))`. This field is immutable.
`consts`[]
  The remaining fields in the function object are references to other CLISP objects. These references are immutable, which is why they are called “constants”. (The referenced CLISP objects can be mutable objects, such as `CONS`es or `VECTOR`s, however.)

### The Exception to the Immutability Rule

When a generic function's dispatch code is installed, the `codevec` and `consts` fields are destructively modified.

Some of the `consts` can play special roles. A function looks like this, in more detail:

name
  see name.
`codevec`
  see `codevec`.
`venv-const`*
  At most one object, representing the closed-up variables, representing the variables of the lexical environment in which this function was defined. It is a `SIMPLE-VECTOR`, which looks like this: `#(`next` `value1` ... `valuen`)` where `value1`, ..., `valuen` are the values of the closed-up variables, and `next` is either `NIL` or a `SIMPLE-VECTOR` having the same structure.
`block-const`*
  Objects representing closed-up `BLOCK` tags, representing the `BLOCK` tags of the lexical environment in which this function was defined. Each is a `CONS` containing in the `CDR` part: either a frame pointer to the block frame, or `#<DISABLED>`. The `CAR` is the block's name, for error messages only.
`tagbody-const`*
  Objects representing closed-up `TAGBODY` tags, representing the `TAGBODY` tags of the lexical environment in which this function was defined. Each is a `CONS` containing in the `CDR` part: either a frame pointer to the `TAGBODY` frame, or `#<DISABLED>` if the `TAGBODY` has already been left. The `CAR` is a `SIMPLE-VECTOR` containing the names of the `TAGBODY` tags, for error messages only.
`keyword-const`*
  If the function was defined with a lambda list containing `&KEY`, here come the symbols ("keywords"), in their correct order. They are used by the interpreter during function call.
`other-const`*
  Other objects needed by the function's bytecode.

If `venv-const`, `block-const`, `tagbody-const` are all absent, the function is called autonomous. This is the case if the function does not refer to lexical variables, blocks or tags defined in compile code outside of the function. In particular, it is the case if the function is defined in a null lexical environment.

If some `venv-const`, `block-const`, or `tagbody-const` are present, the function (a “closure”) is created at runtime. The compiler only generates a prototype, containing `NIL` values instead of each `venv-const`, `block-const`, `tagbody-const`. At runtime, a function is created by copying this prototype and replacing the `NIL` values by the definitive ones.

The list `(`keyword-const`* `other-const`*)` normally does not contain duplicates, because the compiler removes duplicates when possible. (Duplicates can occur nevertheless, through the use of `LOAD-TIME-VALUE`.)

The `codevec` looks like this (cf. the C type Codevec):

`spdepth_1` (2 bytes)
  The 1st part of the maximal `SP` depth.
`spdepth_jmpbufsize` (2 bytes)
  The `jmpbufsize` part of the maximal `SP` depth. The maximal `SP` depth (precomputed by the compiler) is given by `spdepth_1 + spdepth_jmpbufsize * `jmpbufsize``.
`numreq` (2 bytes)
  Number of required parameters.
`numopt` (2 bytes)
  Number of optional parameters.
`flags` (1 byte)
  bit 0
    set if the function has the `&REST` parameter
  bit 7
    set if the function has `&KEY` parameters
  bit 6
    set if the function has `&ALLOW-OTHER-KEYS`
  bit 4
    set if the function is a generic function
  bit 3
    set if the function is a generic function and its effective method shall be returned (instead of being executed)
  bit 2
    set if the full original lambda list is kept in the closure object, see Section 3.3.7, “Declaration `SPACE`”
  bit 1
    set if the `FUNCTION` `DOCUMENTATION` `STRING` is kept in the closure object, see Section 3.3.7, “Declaration `SPACE`”
`signature` (1 byte)
  An abbreviation code depending on `numreq`, `numopt`, `flags`. It is used for speeding up the function call.
`numkey` (2 bytes, only if the function has `&KEY`)
  The number of `&KEY` parameters.
`keyconsts` (2 bytes, only if the function has `&KEY`)
  The offset of the `keyword-const` in the function.
`byte`* (any number of bytes)
  The bytecode instructions.

## 37.4. The general structure of the instructions

All instructions consist of one byte, denoting the opcode, and some number of operands.

The conversion from a byte (in the range 0..255) to the opcode is performed by lookup in the table contained in the file `bytecode.d`.

There are the following types of operands, denoted by different letters:

`k`, `n`, `m`, `l`
  A (nonnegative) numeric operand. The next byte is read. If its bit 7 is zero, then the bits 6..0 give the value (7 bits). If its bit 7 is one, then the bits 6..0 and the subsequent byte together form the value (15 bits).
`b`
  A (nonnegative) 1-byte operand. The next byte is read and is the value.
`label`
  A label operand. A signed numeric operand is read: The next byte is read. If its bit 7 is zero, then the bits 6..0 give the value (7 bits, sign-extended). If its bit 7 is one, then the bits 6..0 and the subsequent byte together form the value (15 bits, sign-extended). If the latter 15-bit result is zero, then four more bytes are read and put together (32 bits, sign-extended). Finally, the bytecode pointer for the target is computed as the current bytecode pointer (pointing after the operand just read), plus the signed numeric operand.

## 37.5. The instruction set

### 37.5.1. Instructions for constants

mnemonic | description | semantics
--- | --- | ---
`(`NIL`)` | Load `NIL` into `values`. | `value1` := `NIL`, `mv_count` := 1
`(PUSH-NIL `n`)` | Push `n` `NIL`s into the `STACK`. | `n` times do: *--`STACK` := `NIL`, Invalidate `values`.
`(`T`)` | Load `T` into `values`. | `value1` := `T`, `mv_count` := 1
`(CONST `n`)` | Load the function's `n`th constant into `values`. | `value1` := `consts`[`n`], `mv_count` := 1

### 37.5.2. Instructions for lexical variables

mnemonic | description | semantics
--- | --- | ---
`(LOAD `n`)` | Load a directly accessible local variable into `values`. | `value1` := *(`STACK`+`n`), `mv_count` := 1
`(LOADI `k1` `k2` `n`)` | Load an indirectly accessible local variable into `values`. | `k` := `k1` + `jmpbufsize` * `k2`, `value1` := *(*(`SP`+`k`)+ `n`), `mv_count` := 1
`(LOADC `n` `m`)` | Load a closed-up variable, defined in the same function and directly accessible, into `values`. | `value1` := `SVREF`(*(`STACK`+`n`),1+`m`), `mv_count` := 1
`(LOADV `k` `m`)` | Load a closed-up variable, defined in an outer function, into `values`. | `v` := `venv-const`, `m` times do: `v` := `SVREF`(`v`,0), `value1` := `SVREF`(`v`,`m`), `mv_count` := 1
`(LOADIC `k1` `k2` `n` `m`)` | Load a closed-up variable, defined in the same function and indirectly accessible, into `values`. | `k` := `k1` + `jmpbufsize` * `k2`, `value1` := `SVREF`(*(*(`SP`+`k`)+`n`),1+`m`), `mv_count` := 1
`(STORE `n`)` | Store values into a directly accessible local variable. | *(`STACK`+`n`) := `value1`, `mv_count` := 1
`(STOREI `k1` `k2` `n`)` | Store values into an indirectly accessible local variable. | `k` := `k1` + `jmpbufsize` * `k2`, *(*(`SP`+`k`)+ `n`) := `value1`, `mv_count` := 1
`(STOREC `n` `m`)` | Store values into a closed-up variable, defined in the same function and directly accessible. | `SVREF`(*(`STACK`+`n`),1+m) := `value1`, `mv_count` := 1
`(STOREV `k` `m`)` | Store values into a closed-up variable, defined in an outer function. | `v` := `venv-const`, `m` times do: `v` := `SVREF`(`v`,0), `SVREF`(`v`,`m`) := `value1`, `mv_count` := 1
`(STOREIC `k1` `k2` `n` `m`)` | Store values into a closed-up variable, defined in the same function and indirectly accessible. | `k` := `k1` + `jmpbufsize` * `k2`, `SVREF`(*(*(`SP`+`k`)+`n`),1+`m`) := `value1`, `mv_count` := 1

### 37.5.3. Instructions for dynamic variables

mnemonic | description | semantics
--- | --- | ---
`(GETVALUE `n`)` | Load a symbol's value into `values`. | `value1` := symbol-value(`consts`[`n`]), `mv_count` := 1
`(SETVALUE `n`)` | Store values into a symbol's value. | symbol-value(`consts`[`n`]) := `value1`, `mv_count` := 1
`(BIND `n`)` | Bind a symbol dynamically. | Bind the value of the symbol `consts`[`n`] to `value1`, implicitly `STACK` -= 3, Invalidate `values`.
`(UNBIND1)` | Dissolve one binding frame. | Unbind the binding frame `STACK` is pointing to, implicitly `STACK` += 3
`(UNBIND `n`)` | Dissolve `n` binding frames. | `n` times do: Unbind the binding frame `STACK` is pointing to, thereby incrementing `STACK` Thus, `STACK` += 1+2*`n`
`(PROGV)` | Bind a set of symbols dynamically to a set of values. | `symbols` := *`STACK`++, *--`SP` := `STACK`, build a single binding frame binding the symbols in `symbols` to the values in `value1`, Invalidate `values`.

### 37.5.4. Instructions for stack operations

mnemonic | description | semantics
--- | --- | ---
`(PUSH)` | Push one object onto the `STACK`. | *--`STACK` := `value1`, Invalidate `values`.
`(POP)` | Pop one object from the `STACK`, into `values`. | `value1` := *`STACK`++, `mv_count` := 1
`(SKIP `n`)` | Restore a previous `STACK` pointer. Remove `n` objects from the `STACK`. | `STACK` := `STACK` + `n`
`(SKIPI `k1` `k2` `n`)` | Restore a previous `STACK` pointer. Remove an unknown number of objects from the `STACK`. | `k` := `k1` + `jmpbufsize` * `k2`, `STACK` := *(`SP`+`k`), `SP` := `SP`+`k`+1, `STACK` := `STACK` + `n`
`(SKIPSP `k1` `k2`)` | Restore a previous `SP` pointer. | `k` := `k1` + `jmpbufsize` * `k2`, `SP` := `SP`+`k`

### 37.5.5. Instructions for control flow, jumps

mnemonic | description | semantics
--- | --- | ---
`(SKIP&RET `n`)` | Clean up the `STACK`, and return from the function. | `STACK` := `STACK`+`n`, return from the function, returning values.
`(SKIP&RETGF `n`)` | Clean up the `STACK`, and return from the generic function. | If bit 3 is set in the function's `flags`, then `STACK` := `STACK`+`n`, `mv_count` := 1, and return from the function. Otherwise: if the current function has no `&REST` argument, then `STACK` := `STACK`+`n`-`numreq`, apply `value1` to the `numreq` arguments still on the `STACK`, and return from the function. Else `STACK` := `STACK`+`n`-`numreq`-1, apply `value1` to the `numreq` arguments and the `&REST` argument, all still on the `STACK`, and return from the function.
`(JMP `label`)` | Jump to `label`. | PC := `label`.
`(JMPIF `label`)` | Jump to `label`, if `value1` is true. | If `value1` is not `NIL`, PC := `label`.
`(JMPIFNOT `label`)` | Jump to `label`, if `value1` is false. | If `value1` is `NIL`, PC := `label`.
`(JMPIF1 `label`)` | Jump to `label` and forget secondary values, if `value1` is true. | If `value1` is not `NIL`, `mv_count` := 1, PC := `label`.
`(JMPIFNOT1 `label`)` | Jump to `label` and forget secondary values, if `value1` is false. | If `value1` is `NIL`, `mv_count` := 1, PC := `label`.
`(JMPIFATOM `label`)` | Jump to `label`, if `value1` is not a cons. | If `value1` is not a cons, PC := `label`. Invalidate `values`.
`(JMPIFCONSP `label`)` | Jump to `label`, if `value1` is a cons. | If `value1` is a cons, PC := `label`. Invalidate `values`.
`(JMPIFEQ `label`)` | Jump to `label`, if `value1` is `EQ` to the top-of-stack. | If eq(`value1`,*`STACK`++), PC := `label`. Invalidate `values`.
`(JMPIFNOTEQ `label`)` | Jump to `label`, if `value1` is not `EQ` to the top-of-stack. | If not eq(`value1`,*`STACK`++), PC := `label`. Invalidate `values`.
`(JMPIFEQTO `n` `label`)` | Jump to `label`, if the top-of-stack is `EQ` to a constant. | If eq(*`STACK`++,`consts`[`n`]), PC := `label`. Invalidate `values`.
`(JMPIFNOTEQTO `n` `label`)` | Jump to `label`, if the top-of-stack is not `EQ` to a constant. | If not eq(*`STACK`++,`consts`[`n`]), PC := `label`. Invalidate `values`.
`(JMPHASH `n` `label`)` | Table-driven jump, depending on `value1`. | Lookup `value1` in the hash table `consts`[`n`]. (The hash table's test is either `EQ` or `EQL`.) If found, the hash table value is a signed `FIXNUM`, jump to it: PC := PC + value. Else jump to `label`. Invalidate `values`.
`(JMPHASHV `n` `label`)` | Table-driven jump, depending on `value1`, inside a generic function. | Lookup `value1` in the hash table `SVREF`(`consts`[0],`n`). (The hash table's test is either `EQ` or `EQL`.) If found, the hash table value is a signed `FIXNUM`, jump to it: PC := PC + value. Else jump to `label`. Invalidate `values`.
`(JSR `label`)` | Subroutine call. | *--`STACK` := function. Then start interpreting the bytecode at `label`, with `values` undefined. When a `(RET)` is encountered, program execution is resumed at the instruction after `(JSR `label`)`.
`(JMPTAIL `m` `n` `label`)` | Tail subroutine call. | `n` `>=` `m`. The `STACK` frame of size `n` is reduced to size `m`: {*(`STACK`+`n`-`m`), ..., *(`STACK`+`n`-1)} := {*`STACK`, ..., *(`STACK`+`m`-1)}. `STACK` += n-m. *--`STACK` := function. Then jump to `label`, with `values` undefined.

### 37.5.6. Instructions for lexical environment, creation of closures

mnemonic | description | semantics
--- | --- | ---
`(VENV)` | Load the `venv-const` into `values`. | `value1` := `consts`[0], `mv_count` := 1.
`(MAKE-VECTOR1&PUSH `n`)` | Create a `SIMPLE-VECTOR` used for closed-up variables. | `v` := new `SIMPLE-VECTOR` of size `n`+1. `SVREF`(`v`,0) := `value1`. *--`STACK` := `v`. Invalidate `values`.
`(COPY-CLOSURE `m` `n`)` | Create a closure by copying the prototype and filling in the lexical environment. | `f` := copy-function(`consts`[`m`]). For `i`=0,..,`n`-1: `f`_`consts`[i] := *(`STACK`+`n`-1-`i`). `STACK` += `n`. `value1` := `f`, `mv_count` := 1

### 37.5.7. Instructions for function calls

mnemonic | description | semantics
--- | --- | ---
`(CALL `k` `n`)` | Calls a constant function with `k` arguments. | The function `consts`[`n`] is called with the arguments *(`STACK`+`k`-1), ..., *(`STACK`+0). `STACK` += `k`. The returned values go into `values`.
`(CALL0 `n`)` | Calls a constant function with 0 arguments. | The function `consts`[`n`] is called with 0 arguments. The returned values go into `values`.
`(CALL1 `n`)` | Calls a constant function with 1 argument. | The function `consts`[`n`] is called with one argument *`STACK`. `STACK` += 1. The returned values go into `values`.
`(CALL2 `n`)` | Calls a constant function with 2 arguments. | The function `consts`[`n`] is called with two arguments *(`STACK`+1) and *(`STACK`+0). `STACK` += 2. The returned values go into `values`.
`(CALLS1 `b`)` | Calls a system function with no `&REST`. | Calls the system function `FUNTAB`[`b`]. The right number of arguments is already on the `STACK` (including `#<UNBOUND>`s in place of absent `&OPTIONAL` or `&KEY` parameters). The arguments are removed from the `STACK`. The returned values go into `values`.
`(CALLS2 `b`)` | Calls a system function with no `&REST`. | Calls the system function `FUNTAB`[256+`b`]. The right number of arguments is already on the `STACK` (including `#<UNBOUND>`s in place of absent `&OPTIONAL` or `&KEY` parameters). The arguments are removed from the `STACK`. The returned values go into `values`.
`(CALLSR `m` `b`)` | Calls a system function with `&REST`. | Calls the system function `FUNTAB`R[`b`]. The minimum number of arguments is already on the `STACK`, and `m` additional arguments as well. The arguments are removed from the `STACK`. The returned values go into `values`.
`(CALLC)` | Calls a computed compiled function with no `&KEY`s. | Calls the compiled function `value1`. The right number of arguments is already on the `STACK` (including `#<UNBOUND>`s in place of absent `&OPTIONAL` parameters). The arguments are removed from the `STACK`. The returned values go into `values`.
`(CALLCKEY)` | Calls a computed compiled function with `&KEY`s. | Calls the compiled function `value1`. The right number of arguments is already on the `STACK` (including `#<UNBOUND>`s in place of absent `&OPTIONAL` or `&KEY` parameters). The arguments are removed from the `STACK`. The returned values go into `values`.
`(FUNCALL `n`)` | Calls a computed function. | Calls the function *(`STACK`+`n`) with the arguments *(`STACK`+`n`-1), ..., *(`STACK`+0). `STACK` += `n`+1. The returned values go into `values`.
`(APPLY `n`)` | Calls a computed function with an unknown number of arguments. | Calls the function *(`STACK`+`n`) with the arguments *(`STACK`+`n`-1), ..., *(`STACK`+0) and a list of additional arguments `value1`. `STACK` += `n`+1. The returned values go into `values`.

### 37.5.8. Instructions for optional and keyword parameters

mnemonic | description | semantics
--- | --- | ---
`(PUSH-UNBOUND `n`)` | Push `n` `#<UNBOUND>`s into the `STACK`. | `n` times do: *--`STACK` := `#<UNBOUND>`. Invalidate `values`.
`(UNLIST `n` `m`)` | Destructure a proper `LIST`. | 0 ≤ `m` ≤ `n`. `n` times do: *--`STACK` := `CAR`(`value1`), `value1` := `CDR`(`value1`). During the last `m` iterations, the list `value1` may already have reached its end; in this case, *--`STACK` := `#<UNBOUND>`. At the end, `value1` must be `NIL`. Invalidate `values`.
`(UNLIST* `n` `m`)` | Destructure a proper or dotted `LIST`. | 0 ≤ `m` ≤ `n`, `n` > 0. `n` times do: *--`STACK` := `CAR`(`value1`), `value1` := `CDR`(`value1`). During the last `m` iterations, the list `value1` may already have reached its end; in this case, *--`STACK` := `#<UNBOUND>`. At the end, after `n` `CDR`s, *--`STACK` := `value1`. Invalidate `values`.
`(JMPIFBOUNDP `n` `label`)` | Jump to `label`, if a local variable is not unbound. | If *(`STACK`+`n`) is not `#<UNBOUND>`, `value1` := *(`STACK`+`n`), `mv_count` := 1, PC := `label`. Else: Invalidate `values`..
`(BOUNDP `n`)` | Load `T` or `NIL` into `values`, depending on whether a local variable is bound. | If *(`STACK`+`n`) is not `#<UNBOUND>`, `value1` := `T`, `mv_count` := 1. Else: `value1` := `NIL`, `mv_count` := 1.
`(UNBOUND->NIL `n`)` | If a local variable is unbound, assign a default value `NIL` to it. | If *(`STACK`+`n`) is `#<UNBOUND>`, *(`STACK`+`n`) := `NIL`.

### 37.5.9. Instructions for multiple values

mnemonic | description | semantics
--- | --- | ---
`(VALUES0)` | Load no values into `values`. | `value1` := `NIL`, `mv_count` := 0
`(VALUES1)` | Forget secondary values. | `mv_count` := 1
`(`STACK`-TO-MV `n`)` | Pop the first `n` objects from `STACK` into `values`. | Load values(*(`STACK`+`n`-1),...,*(`STACK`+0)) into values. `STACK` += `n`.
`(MV-TO-`STACK`)` | Save values on `STACK`. | Push the `mv_count` values onto the `STACK` (in order: `value1` comes first). `STACK` -= `mv_count`. Invalidate `values`.
`(NV-TO-`STACK` `n`)` | Save `n` values on `STACK`. | Push the first `n` values onto the `STACK` (in order: `value1` comes first). `STACK` -= `n`. Invalidate `values`.
`(MV-TO-LIST)` | Convert multiple values into a list. | `value1` := list of values, `mv_count` := 1
`(LIST-TO-MV)` | Convert a `LIST` into multiple values. | Call the function `VALUES-LIST` with `value1` as argument. The returned values go into `values`.
`(MVCALLP)` | Start a `MULTIPLE-VALUE-CALL` invocation. | *--`SP` := `STACK`. *--`STACK` := `value1`.
`(MVCALL)` | Finish a `MULTIPLE-VALUE-CALL` invocation. | newSTACK := *`SP`++. Call the function *(newSTACK-1), passing it *(newSTACK-2), ..., *(`STACK`+0) as arguments. `STACK` := newSTACK. The returned values go into `values`.

### 37.5.10. Instructions for `BLOCK` and `RETURN-FROM`

mnemonic | description | semantics
--- | --- | ---
`(BLOCK-OPEN `n` `label`)` | Create a `BLOCK` frame. | Create a `BLOCK` frame, `STACK` -= 3, `SP` -= 2+`jmpbufsize`. The topmost (third) object in the block frame is `CONS`(`consts`[`n`],frame-pointer) (its `block-cons`). Upon a `RETURN-FROM` to this frame, execution will continue at `label`. Invalidate `values`..
`(BLOCK-CLOSE)` | Dissolve a `BLOCK` frame. | Dissolve the `BLOCK` frame at `STACK`, `STACK` += 3, `SP` += 2+`jmpbufsize`. Mark the `block-cons` as invalid.
`(RETURN-FROM `n`)` | Leave a `BLOCK` whose `block-cons` is given. | `block-cons` := `consts`[`n`]. If `CDR`(`block-cons`) = `#<DISABLED>`, an `ERROR` is `SIGNAL`ed. Else `CDR`(`block-cons`) is a frame-pointer. Unwind the stack up to this frame, pass it values.
`(RETURN-FROM-I `k1` `k2` `n`)` | Leave a `BLOCK` whose `block-cons` is indirectly accessible. | `k` := `k1` + `jmpbufsize` * `k2`, `block-cons` := *(*(`SP`+`k`)+`n`). If `CDR`(`block-cons`) = `#<DISABLED>`, an `ERROR` is `SIGNAL`ed. Else `CDR`(`block-cons`) is a frame-pointer. Unwind the stack up to this frame, pass it values.

### 37.5.11. Instructions for `TAGBODY` and `GO`

mnemonic | description | semantics
--- | --- | ---
`(TAGBODY-OPEN `m` `label1` ... `labeln`)` | Create a `TAGBODY` frame. | Fetch `consts`[`m`], this is a `SIMPLE-VECTOR` with `n` elements, then decode `n` label operands. Create a `TAGBODY` frame, `STACK` -= 3+`n`, `SP` -= 1+`jmpbufsize`. The third object in the `TAGBODY` frame is `CONS`(`consts`[`m`],frame-pointer) (the `tagbody-cons`) Upon a `GO` to tag `label` of this frame, execution will continue at `labell`. Invalidate `values`.
`(TAGBODY-CLOSE-NIL)` | Dissolve a `TAGBODY` frame, and load `NIL` into `values`. | Dissolve the `TAGBODY` frame at `STACK`, `STACK` += 3+`m`, `SP` += 1+`jmpbufsize`. Mark the `tagbody-cons` as invalid. `value1` := `NIL`, `mv_count` := 1.
`(TAGBODY-CLOSE)` | Dissolve a `TAGBODY` frame. | Dissolve the `TAGBODY` frame at `STACK`, `STACK` += 3+`m`, `SP` += 1+`jmpbufsize`. Mark the `tagbody-cons` as invalid.
`(GO `n` `label`)` | Jump into a `TAGBODY` whose `tagbody-cons` is given. | `tagbody-cons` := `consts`[`n`]. If `CDR`(`tagbody-cons`) = `#<DISABLED>`, an `ERROR` is `SIGNAL`ed. Else `CDR`(`tagbody-cons`) is a frame-pointer. Unwind the stack up to this frame, pass it the number `label`.
`(GO-I `k1` `k2` `n` `label`)` | Jump into a `TAGBODY` whose `tagbody-cons` is indirectly accessible. | `k` := `k1` + `jmpbufsize` * `k2`, `tagbody-cons` := *(*(`SP`+`k`)+`n`). If `CDR`(`tagbody-cons`) = `#<DISABLED>`, an `ERROR` is `SIGNAL`ed. Else `CDR`(`tagbody-cons`) is a frame-pointer. Unwind the stack up to this frame, pass it the number `label`.

### 37.5.12. Instructions for `CATCH` and `THROW`

mnemonic | description | semantics
--- | --- | ---
`(CATCH-OPEN `label`)` | Create a `CATCH` frame. | Create a `CATCH` frame, with `value1` as tag. `STACK` -= 3, `SP` -= 2+`jmpbufsize`. Upon a `THROW` to this tag execution continues at `label`.
`(CATCH-CLOSE)` | Dissolve a `CATCH` frame. | Dissolve the `CATCH` frame at `STACK`. `STACK` += 3, `SP` += 2+`jmpbufsize`.
`(THROW)` | Non-local exit to a `CATCH` frame. | `tag` := *`STACK`++. Search the innermost `CATCH` frame with tag `tag` on the `STACK`, unwind the stack up to it, pass it values.

### 37.5.13. Instructions for `UNWIND-PROTECT`

mnemonic | description | semantics
--- | --- | ---
`(UNWIND-PROTECT-OPEN `label`)` | Create an `UNWIND-PROTECT` frame. | Create an `UNWIND-PROTECT` frame. `STACK` -= 2, `SP` -= 2+`jmpbufsize`. When the stack will be unwound by a non-local exit, values will be saved on `STACK`, and execution will be transferred to `label`.
`(UNWIND-PROTECT-NORMAL-EXIT)` | Dissolve an `UNWIND-PROTECT` frame, and start the cleanup code. | Dissolve the `UNWIND-PROTECT` frame at `STACK`. `STACK` += 2, `SP` += 2+`jmpbufsize`. *--`SP` := 0, *--`SP` := 0, *--`SP` := `STACK`. Save the values on the `STACK`, `STACK` -= `mv_count`.
`(UNWIND-PROTECT-CLOSE)` | Terminate the cleanup code. | newSTACK := *`SP`++. Load values(*(newSTACK-1), ..., *(`STACK`+0)) into `values`. `STACK` := newSTACK. SPword1 := *`SP`++, SPword2 := *`SP`++. Continue depending on SPword1 and SPword2. If both are 0, simply continue execution. If SPword2 is 0 but SPword1 is nonzero, interpret it as a label and jump to it.
`(UNWIND-PROTECT-CLEANUP)` | Dissolve an `UNWIND-PROTECT` frame, and execute the cleanup code like a subroutine call. | Dissolve the `UNWIND-PROTECT` frame at `STACK`, get `label` out of the frame. `STACK` += 2, `SP` += 2+`jmpbufsize`. *--`SP` := 0, *--`SP` := PC, *--`SP` := `STACK`. Save the values on the `STACK`, `STACK` -= `mv_count`. PC := `label`.

### 37.5.14. Instructions for `HANDLER-BIND`

mnemonic | description | semantics
--- | --- | ---
`(HANDLER-OPEN `n`)` | Create a handler frame. | Create a handler frame, using `consts`[`n`] which contains the `CONDITION` types, the corresponding labels and the current `SP` depth (= function entry `SP` - current `SP`).
`(HANDLER-BEGIN&PUSH)` | Start a handler. | Restore the same `SP` state as after the HANDLER-OPEN. `value1` := the `CONDITION` that was passed to the handler, `mv_count` := 1. *--`STACK` := `value1`.

### 37.5.15. Instructions for some inlined functions

mnemonic | description | semantics
--- | --- | ---
`(NOT)` | Inlined call to `NOT`. | `value1` := not(`value1`), `mv_count` := 1.
`(EQ)` | Inlined call to `EQ`. | `value1` := eq(*`STACK`++,`value1`), `mv_count` := 1.
`(CAR)` | Inlined call to `CAR`. | `value1` := `CAR`(`value1`), `mv_count` := 1.
`(CDR)` | Inlined call to `CDR`. | `value1` := `CDR`(`value1`), `mv_count` := 1.
`(CONS)` | Inlined call to `CONS`. | `value1` := cons(*`STACK`++,`value1`), `mv_count` := 1.
`(SYMBOL-FUNCTION)` | Inlined call to `SYMBOL-FUNCTION`. | `value1` := `SYMBOL-FUNCTION`(`value1`), `mv_count` := 1.
`(SVREF)` | Inlined call to `SVREF`. | `value1` := `SVREF`(*`STACK`++,`value1`), `mv_count` := 1.
`(SVSET)` | Inlined call to `(`SETF` `SVREF``. | `arg1` := *(`STACK`+1), `arg2` := *(`STACK`+0), `STACK` += 2. `SVREF`(`arg2`,`value1`) := `arg1`. `value1` := `arg1`, `mv_count` := 1.
`(LIST `n`)` | Inlined call to `LIST`. | `value1` := `LIST`(*(`STACK`+`n`-1),...,*(`STACK`+0)), `mv_count` := 1, `STACK` += `n`.
`(LIST* `n`)` | Inlined call to `LIST*`. | `value1` := `LIST*`(*(`STACK`+`n`-1),..., *(`STACK`+0),`value1`), `mv_count` := 1, `STACK` += `n`.

### 37.5.16. Combined instructions

The most frequent short sequences of instructions have an equivalent combined instruction. They are only present for space and speed optimization. The only exception is `FUNCALL&SKIP&RETGF`, which is needed for generic functions.

mnemonic | equivalent
--- | ---
`(NIL&PUSH)` | `(NIL) (PUSH)`
`(T&PUSH)` | `(T) (PUSH)`
`(CONST&PUSH `n`)` | `(CONST `n`) (PUSH)`
`(LOAD&PUSH `n`)` | `(LOAD `n`) (PUSH)`
`(LOADI&PUSH `k1` `k2` `n`)` | `(LOADI `k1` `k2` `n`) (PUSH)`
`(LOADC&PUSH `n` `m`)` | `(LOADC `n` `m`) (PUSH)`
`(LOADV&PUSH `k` `m`)` | `(LOADV `k` `m`) (PUSH)`
`(POP&STORE `n`)` | `(POP) (STORE `n`)`
`(GETVALUE&PUSH `n`)` | `(GETVALUE `n`) (PUSH)`
`(JSR&PUSH `label`)` | `(JSR `label`) (PUSH)`
`(COPY-CLOSURE&PUSH `m` `n`)` | `(COPY-CLOSURE `m` `n`) (PUSH)`
`(CALL&PUSH `k` `n`)` | `(CALL `k` `n`) (PUSH)`
`(CALL1&PUSH `n`)` | `(CALL1 `n`) (PUSH)`
`(CALL2&PUSH `n`)` | `(CALL2 `n`) (PUSH)`
`(CALLS1&PUSH `b`)` | `(CALLS1 `b`) (PUSH)`
`(CALLS2&PUSH `b`)` | `(CALLS2 `b`) (PUSH)`
`(CALLSR&PUSH `m` `n`)` | `(CALLSR `m` `n`) (PUSH)`
`(CALLC&PUSH)` | `(CALLC) (PUSH)`
`(CALLCKEY&PUSH)` | `(CALLCKEY) (PUSH)`
`(FUNCALL&PUSH `n`)` | `(FUNCALL `n`) (PUSH)`
`(APPLY&PUSH `n`)` | `(APPLY `n`) (PUSH)`
`(CAR&PUSH)` | `(CAR) (PUSH)`
`(CDR&PUSH)` | `(CDR) (PUSH)`
`(CONS&PUSH)` | `(CONS) (PUSH)`
`(LIST&PUSH `n`)` | `(LIST `n`) (PUSH)`
`(LIST*&PUSH `n`)` | `(LIST* `n`) (PUSH)`
`(NIL&STORE `n`)` | `(NIL) (STORE `n`)`
`(T&STORE `n`)` | `(T) (STORE `n`)`
`(LOAD&STOREC `k` `n` `m`)` | `(LOAD `k`) (STOREC `n` `m`)`
`(CALLS1&STORE `b` `k`)` | `(CALLS1 `b`) (STORE `k`)`
`(CALLS2&STORE `b` `k`)` | `(CALLS2 `b`) (STORE `k`)`
`(CALLSR&STORE `m` `n` `k`)` | `(CALLSR `m` `n`) (STORE `k`)`
`(LOAD&CDR&STORE `n`)` | `(LOAD `n`) (CDR) (STORE `n`)`
`(LOAD&CONS&STORE `n`)` | `(LOAD `n`+1) (CONS) (STORE `n`)`
`(LOAD&INC&STORE `n`)` | `(LOAD `n`) (CALL1 #'1+) (STORE `n`)`
`(LOAD&DEC&STORE `n`)` | `(LOAD `n`) (CALL1 #'1-) (STORE `n`)`
`(LOAD&CAR&STORE `m` `n`)` | `(LOAD `m`) (CAR) (STORE `n`)`
`(CALL1&JMPIF `n` `label`)` | `(CALL1 `n`) (JMPIF `label`)`
`(CALL1&JMPIFNOT `n` `label`)` | `(CALL1 `n`) (JMPIFNOT `label`)`
`(CALL2&JMPIF `n` `label`)` | `(CALL2 `n`) (JMPIF `label`)`
`(CALL2&JMPIFNOT `n` `label`)` | `(CALL2 `n`) (JMPIFNOT `label`)`
`(CALLS1&JMPIF `b` `label`)` | `(CALLS1 `b`) (JMPIF `label`)`
`(CALLS1&JMPIFNOT `b` `label`)` | `(CALLS1 `b`) (JMPIFNOT `label`)`
`(CALLS2&JMPIF `b` `label`)` | `(CALLS2 `b`) (JMPIF `label`)`
`(CALLS2&JMPIFNOT `b` `label`)` | `(CALLS2 `b`) (JMPIFNOT `label`)`
`(CALLSR&JMPIF `m` `n` `label`)` | `(CALLSR `m` `n`) (JMPIF `label`)`
`(CALLSR&JMPIFNOT `m` `n` `label`)` | `(CALLSR `m` `n`) (JMPIFNOT `label`)`
`(LOAD&JMPIF `n` `label`)` | `(LOAD `n`) (JMPIF `label`)`
`(LOAD&JMPIFNOT `n` `label`)` | `(LOAD `n`) (JMPIFNOT `label`)`
`(LOAD&CAR&PUSH `n`)` | `(LOAD `n`) (CAR) (PUSH)`
`(LOAD&CDR&PUSH `n`)` | `(LOAD `n`) (CDR) (PUSH)`
`(LOAD&INC&PUSH `n`)` | `(LOAD `n`) (CALL1 #'1+) (PUSH)`
`(LOAD&DEC&PUSH `n`)` | `(LOAD `n`) (CALL1 #'1-) (PUSH)`
`(CONST&SYMBOL-FUNCTION `n`)` | `(CONST `n`) (SYMBOL-FUNCTION)`
`(CONST&SYMBOL-FUNCTION&PUSH `n`)` | `(CONST `n`) (SYMBOL-FUNCTION) (PUSH)`
`(CONST&SYMBOL-FUNCTION&STORE `n` `k`)` | `(CONST `n`) (SYMBOL-FUNCTION) (STORE `k`)`
`(APPLY&SKIP&RET `n` `k`)` | `(APPLY `n`) (SKIP&RET `k`)`
`(FUNCALL&SKIP&RETGF `n` `k`)` | `(FUNCALL `n`) (SKIP&RETGF `k`)`

### 37.5.17. Shortcut instructions

There are special one-byte instructions (without explicit operands) for the following frequent instructions:

mnemonic | operand range
--- | ---
`(LOAD `n`)` | 0 ≤ `n` < 15
`(LOAD&PUSH `n`)` | 0 ≤ `n` < 25
`(CONST `n`)` | 0 ≤ `n` < 21
`(CONST&PUSH `n`)` | 0 ≤ `n` < 30
`(STORE `n`)` | 0 ≤ `n` < 8

## 37.6. Examining compiled closures

The functions described here are defined in `src/compiler.lisp` and `src/record.d` and can be used to examine the internals of a compiled closure.

### Warning

These function are internal CLISP functions, their names are not exported, this section is not supposed to be comprehensive and is not guaranteed to be up to date. It is intended for aspiring CLISP hackers who are supposed to graduate to reading the sources right away. All others should stick with the [ANSI CL standard] function `DISASSEMBLE`.

Closure name. The normal way to extract the name of a closure is `FUNCTION-LAMBDA-EXPRESSION`:

    (defun my-plus-1 (x y) (declare (compile)) (+ x y))
    ⇒ MY-PLUS-1
    (function-lambda-expression #'my-plus-1)
    ⇒ (LAMBDA (X Y) (DECLARE (COMPILE)) (+ X Y)) ;
    ⇒ T ;
    ⇒ MY-PLUS-1
    ;; works only on closure objects
    (sys::closure-name #'my-plus-1)
    ⇒ MY-PLUS-1

Closure bytecode. The actual bytecode vector (if you modify it, you can get a segfault when the function is executed):

    (sys::closure-codevec #'my-plus-1)
    ⇒ #(0 0 0 0 2 0 0 0 6 3 174 174 51 2 53 25 3)

Closure constants. A closure can depend on external and internal values:

    (let ((x 123) (y 456))
      (defun my-plus-2 (z) (declare (compile)) (+ x y z)))
    ⇒ MY-PLUS-2
    (sys::closure-consts #'my-plus-2)
    ⇒ (#(Y 456 X 123 NIL) 3 1)

Use `DISASSEMBLE` to see how the constants are used.

Closure signature. Function `SYS::SIGNATURE` returns 8 values:

1. required parameter count
2. optional parameters count
3. rest-p
4. key-p
5. keyword-p
6. allow-other-keys-p
7. byte-list (codevec as a `LIST`)
8. const-list

Mnemonic bytecodes. One can convert between numeric and mnemonic bytecodes (“LAP” stands for “Lisp Assembly Program”):

    (multiple-value-bind (req-num opt-num rest-p key-p keyword-list
                          allow-other-keys-p byte-list const-list)
        (sys::signature #'my-plus-1)
      (sys::disassemble-LAP byte-list const-list))
    ⇒ ((0 LOAD&PUSH 2) (1 LOAD&PUSH 2) (2 CALLSR 2 53) (5 SKIP&RET 3))
    (sys::assemble-LAP (mapcar #'rest *))
    ⇒ (174 174 51 2 53 25 3)

## 37.7. Bytecode Design

This section offers some insight into bytecode design in the form of questions and answers.

### 37.7.1. When to add a new bytecode?

Question:

Does it make sense to define a new bytecode instruction for `RESTART-CASE`? Why? Why not?

#### Answer: Is it speed critical?

`RESTART-CASE` is a glorified `LET` binding for `SYSTEM::*ACTIVE-RESTARTS*` and could well profit from a separate bytecode: it would make it non-consing[3]. (Remember that `RESTART`s have dynamic extent and therefore do not really need to be heap allocated.)

The reason `HANDLER-BIND` has its own bytecodes and `RESTART-CASE` does not is that `HANDLER-BIND` can occur in inner computation loops, whereas `RESTART-CASE` occurs only as part of user-interface programming and therefore not in inner loops where its consing could hurt much.

### 37.7.2. Why JMPTAIL?

Question:

Consider this function and its disassembly:

    (defun foo (x y) (if (or (= x 0) (= y 0)) (+ x y) (foo y (1- x))))
    (DISASSEMBLE 'foo)
    8     (LOAD&PUSH 1)
    9     (LOAD&DEC&PUSH 3)
    11    (JMPTAIL 2 5 L0)

Why are the arguments pushed onto the `STACK`, just to be popped off of it during the `JMPTAIL`? Why not a sequence of `LOAD`, `STORE` and `SKIP` instructions followed by a `JMP`?

#### Answer: This is a shortcut for the most common use

Using `JMPTAIL` requires 3 instructions, `JMP` requires more. When `JMPTAIL` needs to be called, we usually have some stuff close to the top of the `STACK` which will become the new arguments, and some junk between these new arguments and the closure object. `JMPTAIL` removes the junk. `JMPTAIL` is a convenient shortcut which shortens the bytecode - because typically one would really have to clean-up the `STACK` by hand or make the calculations in `src/compiler.lisp` more complicated.

# Part V. Appendices

## Appendix A. Frequently Asked Questions (With Answers) about CLISP

Abstract

This is a list of frequently asked questions about CLISP on the CLISP mailing lists and the USENET newsgroup comp.lang.lisp. All the legitimate technical question are addressed in the CLISP documentation (CLISP impnotes, clisp(1), clisp-link(1)), and for such questions this list provides a link into the docs. The frequently asked political questions are answered here in full detail (meaning that no further explanations of the issues could be provided).

Please submit more questions (and answers!) to clisp-list.

## FAQ

A.1. Meta Information
  A.1.1. Miscellaneous
    A.1.1.1. What is “FAQ fine”?
    A.1.1.2. The official CLISP documentation sucks - is anything better available?
    A.1.1.3. License - why GNU GPL?
    A.1.1.4. What about [ANSI CL standard] compliance?
    A.1.1.5. How do I ask for help?
    A.1.1.6. Which mailing lists should I subscribe to?
    A.1.1.7. Why is my mail to a mailing list rejected?
    A.1.1.8. How do I report bugs?
    A.1.1.9. How do I help?
    A.1.1.10. How do I debug CLISP?
  A.1.2. Logo
    A.1.2.1. Why is CLISP using menorah as the logo?
    A.1.2.2. Shouldn't the logo be changed now due to the current political developments in the Middle East?
    A.1.2.3. Aren't there other political issues of concern?
    A.1.2.4. Aren't you afraid of losing some users who are offended by the logo?
    A.1.2.5. Using software to promote a political agenda is unprofessional!
A.2. Running CLISP
  A.2.1. Why are floats printed in binary?
  A.2.2. Where is the IDE?
  A.2.3. What are the command line arguments?
  A.2.4. How do I get out of the debugger?
  A.2.5. What CLISP extensions are available?
  A.2.6. Where is the init (“RC”) file on my platform?
  A.2.7. Where are the modules with which I built CLISP?
  A.2.8. How do I create a GUI for my CLISP program?
A.3. Application Delivery
  A.3.1. How do I create an executable file with all my code in it?
  A.3.2. When I deliver my application with CLISP, does it have to be covered by the GNU GPL?
A.4. Troubles
  A.4.1. Where is the binary distribution for my platform?
  A.4.2. But a previous release had a binary distribution for my platform, why does not the current one?
  A.4.3. Why does not CLISP build on my platform?
  A.4.4. Why is the --with-libsigsegv-prefix option ignored by the configure script on my 64-bit machine?
  A.4.5. What do charset errors mean?
  A.4.6. What does this message mean: “Display all 1259 possibilities? (y or n)”
  A.4.7. Why does not command line editing work?
  A.4.8. How do I avoid stack overflow?
  A.4.9. Why does my function return different values on each invocation and then hangs forever?
  A.4.10. Is floating point arithmetic broken?
  A.4.11. Is RANDOM broken?
  A.4.12. Why is an extra line break inserted by the pretty printer?
  A.4.13. How do I disable this annoying warning?
  A.4.14. Why does DEFVAR affect previously defined lexical closures?
  A.4.15. The error message is not helpful!
  A.4.16. Why is the function FOO broken?!

### A.1. Meta Information
A.1.1. Miscellaneous A.1.1.1. What is “FAQ fine”? A.1.1.2. The official CLISP documentation sucks - is anything better available? A.1.1.3. License - why GNU GPL? A.1.1.4. What about [ANSI CL standard] compliance? A.1.1.5. How do I ask for help? A.1.1.6. Which mailing lists should I subscribe to? A.1.1.7. Why is my mail to a mailing list rejected? A.1.1.8. How do I report bugs? A.1.1.9. How do I help? A.1.1.10. How do I debug CLISP? A.1.2. Logo A.1.2.1. Why is CLISP using menorah as the logo? A.1.2.2. Shouldn't the logo be changed now due to the current political developments in the Middle East? A.1.2.3. Aren't there other political issues of concern? A.1.2.4. Aren't you afraid of losing some users who are offended by the logo? A.1.2.5. Using software to promote a political agenda is unprofessional!
#### A.1.1. Miscellaneous
A.1.1.1. What is “FAQ fine”? A.1.1.2. The official CLISP documentation sucks - is anything better available? A.1.1.3. License - why GNU GPL? A.1.1.4. What about [ANSI CL standard] compliance? A.1.1.5. How do I ask for help? A.1.1.6. Which mailing lists should I subscribe to? A.1.1.7. Why is my mail to a mailing list rejected? A.1.1.8. How do I report bugs? A.1.1.9. How do I help? A.1.1.10. How do I debug CLISP?
A.1.1.1. | What is “FAQ fine”?
| We levy a fine of 10 zorkmids for asking a question that is answered with a link to this FAQ document. We further levy a fine of 1 zorkmid for asking a question that is answered with a link to the CLISP manual. The fines are payable to the person who answered the questions. The definition of a “zorkmid” is left to the sole discretion of the payer. This should not discourage you from asking questions, but rather encourage you to read the manual and answer questions from other users.
A.1.1.2. | The official CLISP documentation sucks - is anything better available?
| As with all generic complaints, the answer to this one is PTC. Additionally, the nightly builds of the CLISP implementation notes documenting the current Git `default` branch are available at http://clisp.org/beta/impnotes/. It contains both the documentation for the new features and the general improvements in the documentation.
A.1.1.3. | License - why GNU GPL?
| Because CLISP uses GNU readline. Note that this does not necessarily prevent you from distributing your proprietary products based on CLISP. See Note in `COPYRIGHT` and Q: A.3.2.
A.1.1.4. | What about [ANSI CL standard] compliance?
| CLISP purports to conform to the [ANSI CL standard] specification, so all deviations in
    $ clisp -ansi
from the [ANSI CL standard] are bugs and are not (yet) fixed only due to lack of resources. On the other hand, some decisions made by the ANSI X3J13 committee were not as justified from the technical point of view as were most of them, and some of those questionable decisions were made after the alternative behavior has already been implemented in CLISP. The CLISP developers took pains to modify CLISP to unconditionally comply with the [ANSI CL standard] specification in all cases except for a handful of situations where they believed that the committee had made a mistake, in which cases the committee behavior is still optionally available. CLISP does not start in the ansi mode by default for historical reasons and this is not about to change. Dumping an image or passing a command line argument are easy enough.
A.1.1.5. | How do I ask for help?
CLISP | Type help and hit Enter.
Human | Politely - please refer to `Netiquette`. If you have a question about CLISP, you have the following options (listed in the order of decreasing audience size): the USENET newsgroup comp.lang.lisp This is the right place to ask all general Lisp questions, such as "how do I access a character in a string?" CLISP User Mailing List clisp-list This is the right place to ask user-level CLISP-specific questions, such as “"how do I save my CLISP memory image?"”. See also Q: A.1.1.8. CLISP Developer Mailing List clisp-devel This is the right place to discuss CLISP internals, problems with the current development sources, submit patches, offer help. Individual CLISP developers This is never the right thing to do, unless you want to hire this developer to do CLISP consulting (commercial support, custom enhancements etc). This is actually for your own benefit: the CLISP developers are very busy, they might get weeks to answer your question, and some other user may be able to help you in the meantine; as well as for the benefit of the other CLISP users, since the mailing lists are publicly archived (you are encouraged to search them before asking). Please do not copy your messages to the individual developers. ### Mailing lists are member-only To avoid spam, we require that you subscribe before you can post to a mailing list. Alternatively, you can post to the CLISP web forum and your message will be forwarded to the clisp-list mailing list. If you read a list on Gmane and do not want to receive it also by e-mail, you can subscribe to it using the aforementioned web interface and then disable mail delivery. Alternatively, you can ask on StackOverflow with tags `clisp` and/or `common-lisp`.
A.1.1.6. | Which mailing lists should I subscribe to?
| Cross-posting in the CLISP mailing lists is very actively discouraged and is virtually non-existent, thus you can subscribe to all mailing lists that are relevant to you without getting duplicate messages: clisp-announce Extremely low-level moderated list, you should definitely subscribe to this list if you have any interest in Common Lisp or CLISP whatsoever. clisp-list Subscribe to this list of you use CLISP and want to ask (and answer!) questions. If you subscribe to this list, you probably want to subscribe to clisp-announce too. clisp-devel Subscribe to this list if you want to influence CLISP developments; Git commit notes go here (as a daily digest). If you subscribe to this list, you probably want to subscribe to clisp-list and clisp-announce too.
A.1.1.7. | Why is my mail to a mailing list rejected?
| CLISP mailing lists get a lot of spam, so the maintainers have to take care to protect the users. If you get a note that “your message is held for moderator's approval”, you can safely assume that it went to `/dev/null` and try again, noting the following: clisp-announce do not mail here without a prior discussion on clisp-devel or clisp-list clisp-devel subscriber-only, you must post from a subscribed address, no exceptions (see above) clisp-list used to be the only open list (it is closed now), so it is filtered especially aggressively: no `MIME` mail (no HTML formatting, no attachments - send the URL instead) the list address must be in `CC` or `TO`, not `BCC`. do not mention “virgin”, “penis” or “viagra” in the `Subject` line. If you do not like this policy, please volunteer to maintain the mailing lists - you will be required to go through all the “held for moderator's approval” mail and approve/discard as appropriate at least twice a day.
A.1.1.8. | How do I report bugs?
| Patiently!
A.1.1.9. | How do I help?
| Please read Chapter 36, Extending CLISP Core and submit your patch, together with a `src/ChangeLog` entry (see other entries there for inspiration), to clisp-devel (if it is small) or SourceForge patch tracker. See `src/CodingStyle` for the style one should follow. The patch should be created using Git.
A.1.1.10. | How do I debug CLISP?
| Configuring for debugging. Passing `--with-debug` to the top-level configure script does not just replace `-O` with `-g` in the gcc invocation, it also disables some optimizations (registers, assembly, generational garbage-collector) and enables some `printf` calls (mostly before error messages caused by system calls). This means that some bugs might be exhibited by the normal build but not by the `--with-debug` one (and vice versa). If that is the case, please configure normally but edit the `Makefile` and replace the gcc optimization options (`-O` et al) with `-g` before running make. Debugging the core.
    $ ./configure --with-debug --cbc build-g
    $ cd build-g
    $ gdb lisp.run ;; or lisp.exe on Win32 and Cygwin
    (gdb) boot
    (gdb) run
Debugging module `foo`.
    $ ./configure --with-debug --with-module=foo --cbc build-g
    $ cd build-g
    $ gdb full/lisp.run ;; or lisp.exe on Win32 and Cygwin
    (gdb) full
    (gdb) run
When debugging a base module, use base instead of full and boot above. The impact of generational garbage-collector. If your CLISP was built with generational garbage-collector, you will see plenty of spurious segfaults (that's how the generational garbage-collector works). At the end of `src/.gdbinit` you will find the following suggested gdb commands:
    handle SIGSEGV noprint nostop
    break sigsegv_handler_failed
which will stop execution on a dangerous segfault. You can find out whether this is needed by examining the output of the following command:
    $ clisp --version | grep GENERATIONAL_GC
Useful commands. You are encouraged to make use of commands defined in `src/.gdbinit`, such as
boot | run_mod_test | xout
base | run_all_tests | zout
full | run_ansi_tests | zbacktrace
run_test | run_ansi_tests_compiled |
and others; help `command` in gdb will tell you what `command` does. Macros. CLISP makes heavy use of cpp macros (e.g., `pushSTACK`), which can complicate debugging in gdb. The macros are defined in `src/lispbibl.d`, but the maze of conditionals may be hard to navigate. If you are using gcc, you can do make lispbibl.h and then examine the definitions in the generated `lispbibl.h`. See also bottom of `src/spvw_debug.d`. Binary Search in Time. When you encounter a regression error (i.e., something worked in a previous version of CLISP, but does not work in the current version) which we cannot reproduce, we will often ask you to figure out which specific Git commit introduced it. The way to figure that out is to use git bisect.
#### A.1.2. Logo
A.1.2.1. Why is CLISP using menorah as the logo? A.1.2.2. Shouldn't the logo be changed now due to the current political developments in the Middle East? A.1.2.3. Aren't there other political issues of concern? A.1.2.4. Aren't you afraid of losing some users who are offended by the logo? A.1.2.5. Using software to promote a political agenda is unprofessional!
A.1.2.1. | Why is CLISP using menorah as the logo?
Whimsical | If you must have some answer and you do not care whether it is correct or not, you may simply think that Common Lisp brings the Light to a programmer, and CLISP is a vehicle that carries the Light. Accordingly, CLISP enables you to see the truth, thus you can pronounce it as see-lisp. Alternatively, if you are a seasoned expert, you might pronounce it as sea-lisp.
Historical | CLISP has been using the menorah for the logo since the project was first started in the late 1980-ies by Bruno Haible and Michael Stoll. This probably reflects the authors' affection toward the Jewish people, Judaism or the State of Israel (neither of the two original authors is Jewish by birth). You may ask the original authors for details yourself. Both of them are very busy though, so do not expect a prompt reply.
A.1.2.2. | Shouldn't the logo be changed now due to the current political developments in the Middle East?
| The CLISP developers, both the original creators and the current maintainers, do not subscribe to the mainstream view that blames the Jews for everything from high oil prices and Islamic extremism to El Niño and global warming (or cooling, whatever the looming disaster du jour is). Moreover, today, when Jews are being pushed out of the American and European academic institutions with various obscene boycott and divestment campaigns, it is crucial for all of us to stand together against the resurgence of Nazism. For more information, please see: Committee for Accuracy in Middle East Reporting in America Information Regarding Israel's Security Middle East Media Research Institute YES to peace, NO to terror More links
A.1.2.3. | Aren't there other political issues of concern?
| Yes, there are! For example, in 1989 the communist government of the People's Republic of China murdered some 3000+ student human rights protesters at the Tienanmen square in Beijing, and people appear to have already forgotten this crime. A note to that effect was kept in the file `src/timezone.lisp` until 2002, when it was decided that is was not visible enough there and it was moved here. We also oppose software patents and support other liberal (i.e., pro-liberty) causes.
A.1.2.4. | Aren't you afraid of losing some users who are offended by the logo?
| Do you have in mind people like this one? Good riddance!
A.1.2.5. | Using software to promote a political agenda is unprofessional!
| Expressing their opinion is a perfectly natural thing for the authors, be it artistic preferences, political views or religious beliefs. The use of the menorah has its roots somewhere between these areas, and the authors are proud to display it. If you are unlucky enough to have lost the freedom to express your opinion, due to the constraints of a government, society, religion, or expectations of “professional relationships”, the Free World condoles with you. The authors of CLISP are not operating under such constraints. If you are unhappy about their artistic preferences, political views or religious beliefs, you are free to ignore them. Many scientists have been doing art, politics and religion. René Descartes and Isaak Newton combined mathematics and Christianity. Albert Einstein helped the U.S. to counter the danger of an atomic bomb in the hands of the Nazis. Bram Moolenaar, the author of VIM, promotes charitable donations to Uganda.
### A.2. Running CLISP
A.2.1. Why are floats printed in binary? A.2.2. Where is the IDE? A.2.3. What are the command line arguments? A.2.4. How do I get out of the debugger? A.2.5. What CLISP extensions are available? A.2.6. Where is the init (“RC”) file on my platform? A.2.7. Where are the modules with which I built CLISP? A.2.8. How do I create a GUI for my CLISP program?
A.2.1. | Why are floats printed in binary? Where is `DEFUN`?
| Pass `-M` to the runtime (`lisp.run` or `lisp.exe`). Or, better yet, use the driver `clisp` (or `clisp.exe`) instead of invoking the runtime directly.
A.2.2. | Where is the IDE?
Emacs-based | `run-lisp` SLIME ILISP The Common Lisp Cookbook
non-Emacs-based | VisualCLisp Jabberwocky GClisp Portable Hemlock
A.2.3. | What are the command line arguments?
| See clisp(1).
A.2.4. | How do I get out of the debugger?
| See Section 25.1, “Top Level Loop sec_25-1-1”.
A.2.5. | What CLISP extensions are available?
bundled | Quite a few modules are included with CLISP, pass `--with-module=...` to configure to build them and see Q: A.2.7.
3rd party | See the incomplete list of Common Lisp software running in CLISP.
DIY | See Section 32.2, “External Modules” and Section 32.3, “The Foreign Function Call Facility” for information on how to interface with external C libraries.
HTTP | Very Frequently Asked! CLISP comes with `src/inspect.lisp` which implements a rudimentary HTTP server CLOCC/src/donc/ has an HTTP server CLOCC/src/cllib/ handles URLs mod_lisp hooks lisp into Apache Both AllegroServe and CL-HTTP require multithreading and do not work with CLISP yet.
A.2.6. | Where is the init (“RC”) file on my platform?
| Read the file `<clisp.html#opt-norc>` in your build directory or binary distribution (this is the version of the user manual clisp(1) for your platform).
A.2.7. | Where are the modules with which I built CLISP?
| In the full linking set. Run CLISP like this:
    $ clisp -K full
Unless your CLISP was configured with option `--without-dynamic-modules`, you should instead use `(`REQUIRE` `name`)` where `name` is a `STRING`, e.g., “`rawsock`”, or “clx” (for either `clx/new-clx` or `clx/mit-clx`, whichever is installed), or “linux” (for `bindings/glibc`) etc. This is more reliable because the full linking set may include many modules which you do not need and, in fact, cannot use because they require external libraries not installed on your system. Making base the default linking set has some advantages: Shared Library Hell Avoid problems when a module requires a shared library, and that shared library is not present (or is present but with wrong version) on your system. Smaller Images Are Faster Adding things to the heap increases working set size causing a slowdown, which is especially important for small to medium applications. Uniform User Experience Composition of the full linking set is up to the packager, while base is the same on all platforms. See clisp-list for more information (`Gmane/general/8691`/https://sourceforge.net/p/clisp/mailman/message/11678654/).
A.2.8. | How do I create a GUI for my CLISP program?
| Use module `gtk2`: create `ui.glade` with Glade, then do
    $ ./configure --with-module=gtk2 --cbc build-gtk
    $ ./build-gtk/clisp -K full -x '(gtk:run-glade-file "ui.glade")'
There are many other options, see "Common Lisp software running in CLISP".
### A.3. Application Delivery
A.3.1. How do I create an executable file with all my code in it? A.3.2. When I deliver my application with CLISP, does it have to be covered by the GNU GPL?
A.3.1. | How do I create an executable file with all my code in it?
| Use `EXT:SAVEINITMEM`, see also Section 32.6, “Quickstarting delivery with CLISP”.
A.3.2. | When I deliver my application with CLISP, does it have to be covered by the GNU GPL?
| Not necessarily. CLISP is Free Software, covered by the GNU GPL, with special terms governing the distribution of applications that run in CLISP. The precise terms can be found in the `COPYRIGHT` file contained in the source and binary distributions of CLISP. Here is an informal clarification of what these terms mean in practice. Please refer to the said `COPYRIGHT` file when in doubt. In many cases, CLISP does not force an application to be covered by the GNU GPL. Nevertheless, we encourage you to release your software under an open source license. The benefits of such a license for your users are numerous, in particular they are free to modify the application when their needs/requirements change, and they are free to recompile the application when they upgrade their machine or operating system. CLISP extensions, i.e. programs which need to access non-portable CLISP internal symbols (in the packages “SYSTEM”, “CLOS”, “FFI”, etc), must be covered by GNU GPL as well. Other programs running in CLISP have to or need not to be placed under GNU GPL, depending on their distribution form: Programs distributed as Lisp source or `#P".fas"` files can be distributed without restrictions coming from CLISP. Programs distributed as CLISP memory images can be distributed only if accompanied with the non-CLISP `#P".fas"` files which make up the memory image, and a `Makefile` (or clear textual instructions) for rebuilding the memory image. If you need to distribute a modified CLISP executable (for example, incorporating additional modules written in C), you must distribute its full source under GNU GPL. If you are not satisfied with this, you can instead put the additional modules into a separate (non-CLISP) program, with which your Lisp program will communicate via `SOCKET:SOCKET-STREAM`s.
### A.4. Troubles
A.4.1. Where is the binary distribution for my platform? A.4.2. But a previous release had a binary distribution for my platform, why does not the current one? A.4.3. Why does not CLISP build on my platform? A.4.4. Why is the --with-libsigsegv-prefix option ignored by the configure script on my 64-bit machine? A.4.5. What do charset errors mean? A.4.6. What does this message mean: “Display all 1259 possibilities? (y or n)” A.4.7. Why does not command line editing work? A.4.8. How do I avoid stack overflow? A.4.9. Why does my function return different values on each invocation and then hangs forever? A.4.10. Is floating point arithmetic broken? A.4.11. Is RANDOM broken? A.4.12. Why is an extra line break inserted by the pretty printer? A.4.13. How do I disable this annoying warning? A.4.14. Why does DEFVAR affect previously defined lexical closures? A.4.15. The error message is not helpful! A.4.16. Why is the function FOO broken?!
A.4.1. | Where is the binary distribution for my platform?
| The CLISP maintainers do not offer CLISP binary distributions, we believe that software packagers specializing on a particular platform are in a better position to provide quality binaries. Indeed, the section “Get CLISP” on the CLISP's home page points to CLISP packages for all major Linux and *BSD variants. The only exception is Win32 for which there is no centralized packager: usually, after each CLISP release, a CLISP user volunteers to build a Win32 binary package, which we then distribute at https://sourceforge.net/projects/clisp/files/.
A.4.2. | But a previous release had a binary distribution for my platform, why does not the current one?
| It was probably contributed by a user who did not (yet?) contribute a binary distribution for the current release. You can find out who contributed a specific binary distribution by looking at the release notes in the SourceForge Files section.
A.4.3. | Why does not CLISP build on my platform?
| Please see file `unix/PLATFORMS` in your source distribution for information about some known troublesome platforms as well as instructions on porting CLISP to new platforms.
A.4.4. | Why is the `--with-libsigsegv-prefix` option ignored by the configure script on my 64-bit machine?
| See a note on “bi-arch systems” in section 2 of `unix/INSTALL` in your source distribution (for the impatient: pass `--libdir=='${exec_prefix}/lib64'` to the GNU libsigsegv configure). See these threads which discuss the situation in depth:
http://thread.gmane.org/gmane.comp.lib.gnulib.bugs/14565/https://lists.gnu.org/archive/html/bug-gnulib/2008-09/msg00070.html
http://thread.gmane.org/gmane.comp.sysutils.autoconf.general/10827/http://lists.gnu.org/archive/html/autoconf/2008-09/msg00059.html
A.4.5. | What do these error messages mean: “`invalid byte #x94 in CHARSET:ASCII conversion`” and “`character #\u00B3 cannot be represented in the character set CHARSET:ASCII`”?
| This means that you are trying to read (“invalid byte”) or write (“character cannot be represented”) a non-ASCII character from (or to) a character stream which has ASCII `:EXTERNAL-FORMAT`. The default is described in `-E`domain` `encoding``. This may also be caused by filesystem access. If you have files with names incompatible with your `CUSTOM:*PATHNAME-ENCODING*`, filesystem access (e.g., `DIRECTORY`) will `SIGNAL` this `ERROR`. You will need to set `CUSTOM:*PATHNAME-ENCODING*` or pass ``-E`domain` `encoding``` to CLISP. Using a “1:1” encoding, such as `CHARSET:ISO-8859-1`, should help you avoid this error. Note that this error may be signaled by the “Print” part of the read-eval-print loop and not by the function you call. E.g., if file `"foo"` contains non-ASCII characters, you will see such an error when you type
    (WITH-OPEN-FILE (s "foo" :direction :input :EXTERNAL-FORMAT CHARSET:ISO-8859-1)
      (READ-LINE s))
If instead you type
    (WITH-OPEN-FILE (s "foo" :direction :input :EXTERNAL-FORMAT CHARSET:ISO-8859-1)
      (SETQ l (READ-LINE s))
      NIL)
CLISP will just print `NIL` and signal the error when you type `l`.
A.4.6. | What does this message mean: “`Display all 1259 possibilities? (y or n)`”
| CLISP uses GNU readline for command line editing and completion. You get this “Display all 1259 possibilities” message (and sometimes many screens of symbols) when you hit TAB too many times in an inappropriate place. You can turn this feature off if you are using Emacs. It is a good idea not to use TABs in your code.
A.4.7. | Why does not command line editing work?
| See Section 21.2.1, “Command line editing with GNU readline”.
A.4.8. | How do I avoid stack overflow?
| CLISP has two stacks, the “program stack” and the “lisp stack”, and both may occasionally overflow.
Generic | You will always get a stack overflow when you try to print a circular object (`LIST`, `STRUCTURE-OBJECT`, `VECTOR` etc) and `*PRINT-CIRCLE*` is `NIL`. Just set `*PRINT-CIRCLE*` to `T`. You will always get a stack overflow on infinite recursion. Some simple functions (like Ackermann's) recurse more than you might expect and can run out of stack on relatively small inputs. Compiled code uses less stack (and memory) and is faster. If you really do need more Lisp stack, you can increase it by telling CLISP to pre-allocate more memory using `-m` or `MT:MAKE-THREAD`. If you get a segmentation fault after (or instead of) a “program stack overflow” message, please make sure that you had GNU libsigsegv installed when you configured and built CLISP.
Specific | Platform Dependent: Win32 platform only. You have several option, use whichever is applicable to your situation: modify the global `SYSTEM.INI` modify the `PIF` that you use to invoke CLISP (`Gmane/general/4656`/https://sourceforge.net/p/clisp/mailman/message/9033347/) or set the program stack (of the run times base/lisp.exe or full/lisp.exe, not the driver clisp.exe) using editbin (`Gmane/general/5523`/https://sourceforge.net/p/clisp/mailman/message/9033144/); you can find the current stack size using dumpbin. Platform Dependent: UNIX platform only. Increase program stack with ulimit -s (or limit stacksize if you are using `csh`) to at least 8 MB.
A.4.9. | Why does my function return different values on each invocation and then hangs forever?
| The following code modifies itself:
    (defun my-func ()	; modifies internal data!
      (let ((var '(a b c)))
        (nconc var '(1 2 3))))
and will not work as one would naively expect:
    (SETQ *PRINT-CIRCLE* T)
    (FUNCTION-LAMBDA-EXPRESSION #'my-func)
    ⇒ (LAMBDA NIL (DECLARE (SYSTEM::IN-DEFUN MY-FUNC))
     (BLOCK MY-FUNC (LET ((VAR '(A B C))) (NCONC VAR '(1 2 3)))))
    (my-func)	; the first invocation
    ⇒ (a b c 1 2 3)	; modifies the internal data:
    (FUNCTION-LAMBDA-EXPRESSION #'my-func)
    ⇒ (LAMBDA NIL (DECLARE (SYSTEM::IN-DEFUN MY-FUNC))
     (BLOCK MY-FUNC (LET ((VAR '(A B C . #1=(1 2 3)))) (NCONC VAR '#1#))))	; note shared structure!
    (my-func)
    ⇒ (A B C . #1=(1 2 3 . #1#))	; circular list!
    (function-lambda-expression #'my-func )
    ⇒ (LAMBDA NIL (DECLARE (SYSTEM::IN-DEFUN MY-FUNC))
     (BLOCK MY-FUNC (LET ((VAR '(A B C . #1=(1 2 3 . #1#)))) (NCONC VAR '#1#))))	; note circular value of var
    (my-func)	; hangs because NCONC cannot handle a circular argument
Instead you must do
    (defun my-func ()
      (let ((var (copy-list '(a b c))))
        (nconc var (copy-list '(1 2 3)))))
`DISASSEMBLE` will show the constants in your compiled functions (see Chapter 37, The CLISP bytecode specification for the explanation of the `DISASSEMBLE` output.) As you see above, `FUNCTION-LAMBDA-EXPRESSION` works for the interpreted ones. See Lisp Programming Style for more useful information.
A.4.10. | Why don't floating point arithmetic return what I want?
    (- 1.1 0.9)
    ⇒ 0.20000005
inexact | Floating point arithmetic is inherently inexact, so this not a bug, at least not a bug in CLISP. You may argue that this is a bug in IEEE 754, but, before you do, please make sure that you do know What Every Computer Scientist Should Know About Floating-Point Arithmetic (or are at least familiar with the light version thereof). See also clisp-list (`Gmane/general/9850`/https://sourceforge.net/p/clisp/mailman/message/12275968//https://sourceforge.net/p/clisp/mailman/message/12275958/).
exact | If you want exact calculations, use `RATIONAL`s:
    (- 11/10 9/10)
    ⇒ 1/5
A.4.11. | Why does
    $ clisp -x '(RANDOM 1s0)'
always print the same number?
| Reproducibility is important. See Section 12.2.7, “Random-State Operations sec_12-1-7”.
A.4.12. | Why is an extra line break inserted by the pretty printer?
| See the section called “Variable `CUSTOM:*PPRINT-FIRST-NEWLINE*`”. For example, here you are pretty-printing two objects: a one-liner #\Q and a two-liner CR+LF, and a line break is inserted between them so that they are printed on separate lines:
    (defparameter crlf (coerce '(#\Return #\Linefeed) 'string))
    ⇒ CRLF
    (map 'list #'char-code (format nil "Q~a" crlf))
    ⇒ (81 10 13 10)	; not (81 13 10) !
When you want CR+LF-terminated lines, use `:EXTERNAL-FORMAT` `:DOS` argument when opening your `STREAM`s.
A.4.13. | How do I disable this annoying warning?
| CLISP often issues `WARNING`s when it encounters suspicious behavior. It is best to fix your code rather than to suppress them. To figure out where the warning is coming from, do `(`SETQ` `*BREAK-ON-SIGNALS*` '`WARNING`)` and examine the stack in the debugger to see where the warning is coming from. If everything else fails, read the manual.
A.4.14. | Why does `DEFVAR` affect previously defined lexical closures?
    (defun adder (val) (lambda (x) (+ x val)))
    ⇒ ADDER
    (setq add-10 (adder 10))
    ⇒ ADD-10
    (funcall add-10 32)
    ⇒ 42	; as expected
    (defvar val 12)
    ⇒ VAL
    (funcall add-10 0)
    ⇒ 12	; why not 10?!
Explanation | The above code does not conform to [ANSI CL standard], therefore CLISP can produce arbitrary results. See Section 3.2.2.3, “Semantic Constraints sec_3-2-2-3”.
Remedy | Always follow the naming convention for global special variables defined by `DEFVAR` and `DEFPARAMETER` (e.g., `*FOO*`) and `DEFCONSTANT` (e.g., `+BAR+`).
More |
`Gmane/general/11945`/https://sourceforge.net/p/clisp/mailman/message/13174197/
`Gmane/general/11949`/https://sourceforge.net/p/clisp/mailman/message/13174204/
A.4.15. | The error message is not helpful!
| Sometimes an error message contains a compound object whose content you want to examine. Often this object will be available for `INSPECT`ion via the Inspect command (see Table 25.3, “Commands common to the debugger and the stepper”). E.g.,
    *** - READ: input stream #<INPUT STRING-INPUT-STREAM> ends within an object
    The following restarts are available:
    ABORT          :R1      ABORT
    Break 4 [1]> :i
    #<SYSTEM::SIMPLE-END-OF-FILE #x000333CB82F8>:  standard object
     type: SYSTEM::SIMPLE-END-OF-FILE
    0 [$STREAM]:  #<INPUT STRING-INPUT-STREAM>
    1 [$FORMAT-CONTROL]:
    "~S: input stream ~S ends within an object
    "
    2 [$FORMAT-ARGUMENTS]:  (READ #<INPUT STRING-INPUT-STREAM>)
    INSPECT-- type :h for help; :q to return to the REPL ---> 0
    #<INPUT STRING-INPUT-STREAM>:  atom
     type: STRING-STREAM
     class: #1=#<BUILT-IN-CLASS STRING-STREAM>
    INSPECT-- type :h for help; :q to return to the REPL ---> :d

    #<INPUT STRING-INPUT-STREAM> is an input-stream. It reads from "(foo" from 0 to 4 at 4.
A.4.16. | Why is the function `FOO` broken?!
| When confronted with unexpected behavior, try looking in the CLISP impnotes. E.g., CLISP `DIRECTORY` is different from the CMU CL implementation, so, to find out how to get the results you want, you should search the CLISP implementation notes for "DIRECTORY". Alternatively, since the implementation notes are organized in parallel to the [ANSI CL standard], and `DIRECTORY` belongs to the Chapter 20 in [ANSI CL standard], you can just go to Chapter 20, Files chap-20 in impnotes and look for "DIRECTORY" there.

## Appendix B. GNU Free Documentation License

Version 1.3, 3 November 2008

Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

### 0. PREAMBLE

The purpose of this License is to make a manual, textbook, or other functional and useful document “free” in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

### 1. APPLICABILITY AND DEFINITIONS

This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document’s overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is called “Opaque”.

Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work’s title, preceding the beginning of the body of the text.

The “publisher” means any person or entity that distributes copies of the Document to the public.

A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.

The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

### 2. VERBATIM COPYING

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

### 3. COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

### 4. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
4. Preserve all the copyright notices of the Document.
5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document’s license notice.
8. Include an unaltered copy of this License.
9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
15. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version’s license notice. These titles must be distinct from any other section titles.

You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties — for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

### 5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements”.

### 6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

### 7. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

### 8. TRANSLATION

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

### 9. TERMINATION

You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

### 10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See https://www.gnu.org/licenses/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

### 11. RELICENSING

“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

“Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

### ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

    Copyright © YEAR YOUR NAME

    Permission is granted to copy, distribute and/or modify this document under the
    terms of the GNU Free Documentation License, Version 1.3 or any later version
    published by the Free Software Foundation; with no Invariant Sections, no
    Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in
    the section entitled “GNU Free Documentation License”.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with… Texts.” line with this:

    with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts
    being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

## Appendix C. GNU General Public License

Version 2, June 1991

Copyright © 1989, 1991 Free Software Foundation, Inc.

Free Software Foundation, Inc.
51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301
USA

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

Version 2, June 1991

## C.1. Preamble

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software - to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

We protect your rights with two steps:

1. copyright the software, and

2. offer you this license which gives you legal permission to copy, distribute and/or modify the software.

Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.

Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.

The precise terms and conditions for copying, distribution and modification follow.

## C.2. TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

### C.2.1. Section 0

This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The “Program”, below, refers to any such program or work, and a “work based on the Program” means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term “modification”.) Each licensee is addressed as “you”.

Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.

### C.2.2. Section 1

You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.

You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.

### C.2.3. Section 2

You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:

1. You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.

2. You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.

3. If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: If the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)

These requirements apply to the modified work as a whole. If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works. But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.

Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.

In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.

### C.2.4. Section 3

You may copy and distribute the Program (or a work based on it, under Section 2 in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:

1. Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

2. Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

3. Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.)

The source code for a work means the preferred form of the work for making modifications to it. For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable. However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.

If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.

### C.2.5. Section 4

You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

### C.2.6. Section 5

You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works. These actions are prohibited by law if you do not accept this License. Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it.

### C.2.7. Section 6

Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions. You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License.

### C.2.8. Section 7

If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all. For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.

If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.

It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices. Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.

This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.

### C.2.9. Section 8

If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded. In such case, this License incorporates the limitation as if written in the body of this License.

### C.2.10. Section 9

The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

Each version is given a distinguishing version number. If the Program specifies a version number of this License which applies to it and “any later version”, you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.

### C.2.11. Section 10

If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally.

### C.2.12. NO WARRANTY Section 11

BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

### C.2.13. Section 12

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

END OF TERMS AND CONDITIONS

## C.3. How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.

<one line to give the program's name and a brief idea of what it does.> Copyright (C) <year> <name of author>

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it starts in an interactive mode:

Gnomovision version 69, Copyright (C) year name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type “show w”. This is free software, and you are welcome to redistribute it under certain conditions; type “show c” for details.

The hypothetical commands “show w” and “show c” should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than “show w” and “show c”; they could even be mouse-clicks or menu items--whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the program, if necessary. Here is a sample; alter the names:

Yoyodyne, Inc., hereby disclaims all copyright interest in the program “Gnomovision” (which makes passes at compilers) written by James Hacker.

<signature of Ty Coon>, 1 April 1989 Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.

# Index

### Symbols

*COMPILE-WARNINGS*, Function COMPILE-FILE
*COMPILED-FILE-TYPES*, Function LOAD
*CURRENT-LANGUAGE* , The Language
*EDITOR*, Function ED
*EQ-HASHFUNCTION*, Function MAKE-HASH-TABLE
*EQL-HASHFUNCTION*, Function MAKE-HASH-TABLE
*EQUAL-HASHFUNCTION*, Function MAKE-HASH-TABLE
*FOREIGN-ENCODING* , Default encodings
*FORWARD-REFERENCED-CLASS-MISDESIGN*, Inheritance Structure of Metaobject Classes
*INSPECT-LENGTH*, Function INSPECT
*LOAD-COMPILING*, Function LOAD
*LOAD-ECHO*, Function LOAD
*LOAD-OBSOLETE-ACTION*, Function LOAD
*MISC-ENCODING* , Default encodings
*PATHNAME-ENCODING* , Default encodings
*SOURCE-FILE-TYPES*, Function LOAD
*TERMINAL-ENCODING* , Default encodings
*WARN-ON-HASHTABLE-NEEDING-REHASH-AFTER-GC*, Interaction between HASH-TABLEs and garbage-collection
*WINDOW* , Random Screen Access

### C

callback, Overview, Foreign functions
class
  anonymous, Initialization of Anonymous Classes
  finalization, Class Finalization Protocol
  interposed, Implementation and User Specialization

### D

DEFAULT-FOREIGN-LANGUAGE , The choice of the C flavor
DEFINTERNATIONAL , The Language
DEFLANGUAGE, The Language
DEFLOCALIZED, The Language

### E

endianness, Binary input, READ-BYTE, EXT:READ-INTEGER & EXT:READ-FLOAT

### F

final delimiter, Special Symbols sec_1-4-1-3
foreign function, Introduction
  anonymous, Foreign functions
  call-in, Foreign functions
  call-out, Foreign functions
  named, Foreign functions
foreign variable, Foreign variables
FORMAT
  ~!, Formatted Output sec_22-3
  ~., Formatted Output sec_22-3

### G

GC, Function EXT:GC
GENERIC-FLET, Deviations from ANSI CL standard
GENERIC-LABELS, Deviations from ANSI CL standard

### L

linking set, Linking Set
LOCALIZED, The Language

### M

MAKE-BUFFERED-INPUT-STREAM, Functions EXT:MAKE-BUFFERED-INPUT-STREAM and EXT:MAKE-BUFFERED-OUTPUT-STREAM
MAKE-BUFFERED-OUTPUT-STREAM, Functions EXT:MAKE-BUFFERED-INPUT-STREAM and EXT:MAKE-BUFFERED-OUTPUT-STREAM
metaobject, Metaobjects
  class, Classes
  generic function, Generic Functions
  implementation-specific, Implementation and User Specialization
  method, Methods
  method combination, Method Combinations
  portable, Implementation and User Specialization
  slot definition, Slot Definitions
    direct, Slot Definitions
    effective, Slot Definitions
  specializer, Specializers
  specified, Implementation and User Specialization
  standard, Inheritance Structure of Metaobject Classes
metaobject class, Metaobjects
  basic, Metaobjects
method
  effective, Generic Function Invocation Protocol
  extends, Implementation and User Specialization
  function, Generic Function Invocation Protocol, Processing Method Bodies
  overrides, Implementation and User Specialization
  promoted, Implementation and User Specialization
  specialized, Implementation and User Specialization
METHOD-CALL-ERROR, Standard Method Combination sec_7-6-6-2
METHOD-CALL-TYPE-ERROR, Standard Method Combination sec_7-6-6-2
module, Module Set
  name, Module Set
module set, Module Set

### N

NO-PRIMARY-METHOD, Standard Method Combination sec_7-6-6-2

### P

PACKAGE
  case-inverted, Package Case-Sensitivity
  case-sensitive, Package Case-Sensitivity
  modern, Package Case-Sensitivity
PACKAGE-LOCK, Constraints on the “COMMON-LISP” Package for Conforming Programs - package locking sec_11-1-2-1-2

### R

ROOM, Function ROOM

### S

slot
  directly accessible, Instance Structure Protocol
  location, Instance Structure Protocol
SYMBOL-MACRO-EXPAND, Macro DEFINE-SYMBOL-MACRO

### T

TIMES, Macro TIME
token
  reserved, Symbols as Tokens sec_2-3-4
trampoline, Callbacks and memory management

### V

visually similar, Variable CUSTOM:*SUPPRESS-SIMILAR-CONSTANT-REDEFINITION-WARNING*

### W

WITH-OUTPUT-TO-PRINTER , Printing
WITHOUT-PACKAGE-LOCK, Constraints on the “COMMON-LISP” Package for Conforming Programs - package locking sec_11-1-2-1-2

# References

### Books

[CLtL1] Guy L. Steele, Jr.. Common Lisp: the Language (1st Edition). 1984. 465 pages. ISBN 0-932376-41-X. Digital Press.

[CLtL2] Guy L. Steele, Jr.. Common Lisp: the Language (2nd Edition). 1990. 1032 pages. ISBN 1-555-58041-6. Digital Press.

[AMOP] Gregor Kiczales, Jim des Rivieres, and Daniel G. Bobrow. The Art of the Metaobject Protocol. 1991. 335 pages. ISBN 0-262-61074-4. MIT Press.

### ANSI standard documents

[ANSI CL] ANSI CL standard1994. ANSI INCITS 226-1994 (R1999) Information Technology - Programming Language - Common Lisp [formerly ANSI X3.226-1994 (R1999)].

[CLHS] Common Lisp HyperSpecCommon Lisp HyperSpec.

| These notes document CLISP version 2.49.93+ | Last modified: 2020-06-22

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