XLISP unless

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# unless

Type: | - | special form (fsubr)
Source: | - | xlcont.c

## Syntax

(unless test [expr ... ])
  test - an expression, NIL or non-NIL
  expr - expressions comprising a body of code
  returns - the value of the last expression or NIL

## Description

The 'unless' special form executes the 'expr' forms if 'test' evaluates to a NIL value. If 'test' is NIL , the value of the last 'expr' is returned as the result. If 'test' is non-NIL , NIL is returned with none of 'expr' evaluated.

## Examples

    (unless NIL)                    ; returns NIL
    (unless T)                      ; returns NIL

    (unless NIL (print "hi") 'foo)  ; prints "hi"  returns FOO

    (unless (listp "a")
            (print "not a list"))   ; prints  "not a list"
                                    ; returns "not a list"

See the unless special form in the XLISP 2.0 manual.

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Nyquist / XLISP 2.0 - Contents | Tutorials | Examples | Reference