Contributing - Faust Libraries

# Contributing

In general, libraries are organised in a stacked manner: the base ones define functions or constants without any dependancies, and additional ones are gradually built on top of simpler ones, layer by layer. Dependency loops must be avoided as much as possible. The resources folder contains tools to build and visualise the libraries dependencies graphs.

If you wish to add a function to any of these libraries or if you plan to add a new library, make sure that you observe the following conventions:

## New Functions

- All functions must be preceded by a markdown documentation header respecting the following format (open the source code of any of the libraries for an example):

    //-----------------functionName--------------------
    // Description
    //
    // #### Usage
    //
    // ```
    // Usage Example
    // ```
    //
    // Where:
    //
    // * argument1: argument 1 description
    //-------------------------------------------------

- Every time a new function is added, the documentation should be updated simply by running `make doclib`.
- The environment system (e.g. `os.osc`) should be used when calling a function declared in another library (see the section on Library Import).
- Try to reuse existing functions as much as possible.
- The `Usage` line must show the input/output shape (the number of inputs and outputs) of the function, like `gen: _` for a mono generator, `_ : filter : _` for a mono effect, etc.
- Some functions use parameters that are constant numerical expressions. The convention is to label them in capital letters and document them preferably to be constant numerical expressions (or known at compile time in existing libraries).
- Functions with several parameters should better be written by putting the more constant parameters (like control, setup...) at the beginning of the parameter list, and audio signals to be processed at the end. This allows to do partial-application. So prefer the following `clip(low, high, x) = min(max(x, low), high);` form where `clip(-1, 1)` partially applied version can be used later on in different contexts, better than `clip(x, low, high) = min(max(x, low), high);` version.

## New Libraries

- Any new "standard" library should be declared in `stdfaust.lib` with its own environment (2 letters - see `stdfaust.lib`).
- Any new "standard" library must be added to `generateDoc`.
- Functions must be organized by sections.
- Any new library should at least `declare` a `name` and a `version`.
- Any new library has to use a prefix declared in the header section with the following kind of syntax: `Its official prefix is 'qu'` (look at an existing library to follow the exact syntax).
- Be sure to add the appropriate kind of `ma = library("maths.lib");` import library line, for each external library function used in the new library (for instance `ma.foo` that would be used somewhre in the code).
- The comment based markdown documentation of each library must respect the following format (open the source code of any of the libraries for an example):

    //############### libraryName ##################
    // Description
    //
    // * Section Name 1
    // * Section Name 2
    // * ...
    //
    // It should be used using the `[...]` environment:
    //
    // ```
    // [...] = library("libraryName");
    // process = [...].functionCall;
    // ```
    //
    // Another option is to import `stdfaust.lib` which already contains the `[...]`
    // environment:
    //
    // ```
    // import("stdfaust.lib");
    // process = [...].functionCall;
    // ```
    //##############################################

    //================= Section Name ===============
    // Description
    //==============================================

## Coding Conventions

In order to have a uniformized library system, we established the following conventions (that hopefully will be followed by others when making modifications to them).

### Function Naming

[WIP]

JOS proposal: using terms used in the field of digital signal processing, as follows:

- `impulse`: ...,0,1,0,...
- `pulse`: ...,0,1,1,0,... or longer
- `impulse_train`
- `pulse_train`
- `gate` = pulse controlled externally (e.g., by NoteOn,NoteOff)
- `trigger` = impulse controlled externally (gate - gate' > 0) == gate rising edge

[/WIP]

### Variable Argument List

Strictly speaking, there are no lists in Faust. But list operations can be simulated (in part) using the parallel binary composition operation `,` and pattern matching.

Thus functions expecting a variable number of arguments can use this mechanism, like a `foo` function that would be used this way: `foo((a,b,c,d))`. See fi.iir and fi.fir examples.

### Documentation

- All the functions that we want to be "public" are documented.
- We used the `faust2md` "standards" for each library: `//###` for main title (library name - equivalent to `#` in markdown), `//===` for section declarations (equivalent to `##` in markdown) and `//---` for function declarations (equivalent to `####` in markdown - see `basics.lib` for an example).
- Sections in function documentation should be declared as `####` markdown title.
- Each function documentation provides a "Usage" section (see `basics.lib`).
- The full documentation can be generated using the doc/Makefile script. Use `make help` to see all possible commands. If you plan to create a pull-request, do not commit the full generated code but only the modified .lib files.
- Each function can have `declare author "name";`, `declare copyright "XXX";` and `declare licence "YYY";` declarations.
- Each library has a `declare version "xx.yy.zz";` semantic version number to be raised each time a modification is done. The global `version` number in `version.lib` also has to be adapted according to the change.

### Library Import

To prevent cross-references between libraries, we generalized the use of the `library("")` system for function calls in all the libraries. This means that everytime a function declared in another library is called, the environment corresponding to this library needs to be called too. To make things easier, a `stdfaust.lib` library was created and is imported by all the libraries:

    aa = library("aanl.lib");
    sf = library("all.lib");
    an = library("analyzers.lib");
    ba = library("basics.lib");
    co = library("compressors.lib");
    de = library("delays.lib");
    dm = library("demos.lib");
    dx = library("dx7.lib");
    en = library("envelopes.lib");
    fd = library("fds.lib");
    fi = library("filters.lib");
    ho = library("hoa.lib");
    it = library("interpolators.lib");
    la = library("linearalgebra.lib");
    ma = library("maths.lib");
    mi = library("mi.lib");
    ef = library("misceffects.lib");
    os = library("oscillators.lib");
    no = library("noises.lib");
    pf = library("phaflangers.lib");
    pm = library("physmodels.lib");
    qu = library("quantizers.lib");
    rm = library("reducemaps.lib");
    re = library("reverbs.lib");
    ro = library("routes.lib");
    si = library("signals.lib");
    so = library("soundfiles.lib");
    sp = library("spats.lib");
    sy = library("synths.lib");
    ve = library("vaeffects.lib");
    vl = library("version.lib");
    wa = library("webaudio.lib");
    wd = library("wdmodels.lib");

For example, if we wanted to use the `smooth` function which is now declared in `signals.lib`, we would do the following:

    import("stdfaust.lib");

    process = si.smooth(0.999);

This standard is only used within the libraries: nothing prevents coders to still import `signals.lib` directly and call `smooth` without `ro.`, etc. It means symbols and function names defined within a library have to be unique to not collide with symbols of any other libraries.

### "Demo" Functions

"Demo" functions are placed in `demos.lib` and have a built-in user interface (UI). Their name ends with the `_demo` suffix. Each of these function have a `.dsp` file associated to them in the `/examples` folder.

Any function containing UI elements should be placed in this library and respect these standards.

### "Standard" Functions

"Standard" functions are here to simplify the life of new (or not so new) Faust coders. They are declared in `/libraries/doc/standardFunctions.md` and allow to point programmers to preferred functions to carry out a specific task. For example, there are many different types of lowpass filters declared in `filters.lib` and only one of them is considered to be standard, etc.

## Testing the library

Before preparing a pull-request, the new library must be carefully tested:

- all functions defined in the library must be tested by preparing a DSP test program
- the compatibility library `all.lib` imports all libraries in a same namespace, so check functions names collisions using the following test program:

    import("all.lib");
    process = _;

## Library deployment

For GRAME maintainers:

- regenerate the PDF documentation using `make pdf` target in the `doc` folder
- update the library submodule in faust, recompile and deploy WebAssembly libfaust in fausteditor, faustplayground and faustide
- update the library submodule in faustlive
- update the library list in this fausteditor page as well as the snippets (using the `faust2atomsnippets` tool).
- update the library list in this faustide page.
- update the library list in the faustgen~ code
- update the Faust Syntax Highlighting Files
- make an update PR for vscode-faust project

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