DllLoad, DllUnload, DllEnumerate , StubApiCStart , StubApiCShortIntegerConstant , StubApiCInclude , StubApiCFunction , StubApiCRemark , StubApiCSetEnv , StubApiCFile , StubApiCStruct .

# The Yacas plugin structure

Yacas supports dynamically loading libraries at runtime. This chapter describes functions for working with plugins.

DllLoad, DllUnload, DllEnumerate | manipulate plugins
StubApiCStart | start of C++ plugin API
StubApiCShortIntegerConstant | declare integer constant in plugin
StubApiCInclude | declare include file in plugin
StubApiCFunction | declare C++ function in plugin
StubApiCRemark | documentation string in plugin
StubApiCSetEnv | access Yacas environment in plugin
StubApiCFile | set file name for plugin API
StubApiCStruct | declare C struct in plugin

The plugin feature allows Yacas to interface with other libraries that support additional functionality. For example, there could be a plugin enabling the user to script a user interface from within Yacas, or a specific powerful library to do numeric calculations.

The plugin feature is currently in an experimental stage. There are some examples in the `plugins/` directory. These are not built by default because they cannot be guaranteed to compile on every platform (yet). The plugins need to be compiled after Yacas itself has been compiled and installed successfully. The `plugins/` directory contains a `README` file with more details on compilation.

In addition to the plugin structure in the Yacas engine, there is a module `cstubgen` (currently still under development) that allows rapid scripting of a plugin. Essentially all that is required is to write a file that looks like the header file of the original library, but written in Yacas syntax. The module `cstubgen` is then able to write out a C++ file that can be compiled and linked with the original library, and then loaded from within Yacas. Including a function in the plugin will typically take just one line of Yacas code. There are a few examples in the `plugins/` directory (the files ending with api.stub). The file `makefile.plugin` is configured to automatically convert these to the required C++ files. See also an essay on plugins for a worked-out example.

In addition to the C++ stub file, `cstubgen` also automatically generates some documentation on the functions included in the stub. This documentation is put in a file with extension 'description'.

The plugin facility is not supported for each platform yet. Specifically, it is only supported on platforms that support the elf binary format. (Loading DLLs is platform-dependent).

This chapter assumes the reader is comfortable programming in C++.

###

DllLoad, DllUnload, DllEnumerate -- manipulate plugins

##### Internal function

##### Calling format:

    DllLoad(file)
    DllUnload(file)
    DllEnumerate()

##### Parameters:

`file` -- file name of the plugin

##### Description:

`DllLoad` forces Yacas to load the dynamic link library (`.so` file under Linux). The full path to the DLL has to be specified, or the file needs to be in a path where `dlopen` can find it.

`DllUnload` unloads a dynamic link library previously loaded with `DllLoad`. Note the dll file name has to be exactly the same, or the system will not be able to determine which dll to unload. It will scan all the dll files, and delete the first one found to exactly match, and return silently if it didn't find the dll. `DllUnload` always returns `True`.

`DllEnumerate` returns a list with all loaded dynamic link libraries.

##### Example:

    In> DllLoad("./libopengl.so");
    Out> True;

###

StubApiCStart -- start of C++ plugin API

##### Standard library

##### Calling format:

    StubApiCStart(name)

##### Parameters:

`name` -- name of the plugin

##### Description:

To start up generating a c stub file for linking a c library with Yacas. A stub specification file needs to start with this function call, to reset the internal state of Yacas for emitting a stub C++ file. The parameter `name` should identify the plugin uniquely.

##### See also:

StubApiCShortIntegerConstant , StubApiCInclude , StubApiCFunction , StubApiCFile , StubApiCSetEnv .

###

StubApiCShortIntegerConstant -- declare integer constant in plugin

##### Standard library

##### Calling format:

    StubApiCShortIntegerConstant(const,value)

##### Parameters:

`const` -- string representing the global variable to be bound runtime

`value` -- integer value the global should be bound to

##### Description:

define a constant 'const' to have value 'value'. The value should be short integer constant. This is useful for linking in defines and enumerated values into Yacas. If the library for instance has a define

    #define FOO 10

Then

    StubApiCShortIntegerConstant("FOO","FOO")

will bind the global variable FOO to the value for FOO defined in the library header file.

##### See also:

StubApiCStart , StubApiCInclude , StubApiCFunction , StubApiCFile , StubApiCSetEnv .

###

StubApiCInclude -- declare include file in plugin

##### Standard library

##### Calling format:

    StubApiCInclude(file)

##### Parameters:

`file` -- file to include from the library the plugin is based on

##### Description:

Declare an include file (a header file for the library, for instance) The delimiters need to be specified too. So, for a standard library like the one needed for OpenGL, you need to specify

    StubApiCInclude("\<GL/gl.h\>")

and for user include file:

    StubApiCInclude("\"GL/gl.h\"")

##### See also:

StubApiCStart , StubApiCShortIntegerConstant , StubApiCFunction , StubApiCFile , StubApiCSetEnv .

###

StubApiCFunction -- declare C++ function in plugin

##### Standard library

##### Calling format:

    StubApiCFunction(returntype,fname,args)
    StubApiCFunction(returntype,fname,
      fname2,args)

##### Parameters:

`returntype` -- return type of new function

`fname` -- function of built-in function

`fname2` -- (optional) function name to be used from within Yacas

`args` -- list of arguments to the function

##### Description:

This function declares a new library function, along with its calling sequence. `cstubgen` will then generate the C++ code required to call this function.

Return type, function name, and list of arguments should be literal strings (surrounded by quotes).

If `fname2` is not supplied, it will be assumed to be the same as fname.

The return types currently supported are "`int`", "`double`" and "`void`".

The argument values that are currently supported are "`int`", "`double`", and "`input_string`".

Argument types can be specified simply as a string referring to their type, like `"int"`, or they can be lists with an additional element stating the name of the variable: `{"int","n"}`. The variable will then show up in the automatically generated documentation as having the name "n".

##### Examples:

To define an OpenGL function `glVertex3d` that accepts three doubles and returns void:

    StubApiCFunction("void","glVertex3d",
      {"double","double","double"});

##### See also:

StubApiCStart , StubApiCShortIntegerConstant , StubApiCInclude , StubApiCFile , StubApiCSetEnv .

###

StubApiCRemark -- documentation string in plugin

##### Standard library

##### Calling format:

    StubApiCRemark(string)

##### Parameters:

`string` -- comment string to be added to the documentation

##### Description:

StubApiCRemark adds a piece of text to the stub documentation file that gets generated automatically. The documentation is put in a `.description` file while the input file is being processed, so adding a remark on a function just after a function declaration adds a remark on that function.

##### See also:

StubApiCShortIntegerConstant , StubApiCInclude , StubApiCFunction , StubApiCSetEnv , StubApiCFile .

###

StubApiCSetEnv -- access Yacas environment in plugin

##### Standard library

##### Calling format:

    StubApiCSetEnv(func)

##### Parameters:

`func` -- name of the function to call to set the environment variable

##### Description:

This function forces the plugin to call the function func, with as argument `LispEnvironment&` `aEnvironment`. This lets the plugin store the environment class (which is needed for almost any thing to do with Yacas), somewhere in a global variable. aEnvironment can then be used from within a callback function in the plugin that doesn't take the extra argument by design.

There needs to ba a function in the plugin somewhere of the form

    static LispEnvironment* env = NULL;
    void GlutSetEnv(LispEnvironment& aEnv)
    {
        env = &aEnv;
    }

Then calling

    StubApiCSetEnv("GlutSetEnv");

will force the plugin to call GlutSetEnv at load time. All functions in the plugin will then have access to the Yacas environment.

##### See also:

StubApiCStart , StubApiCShortIntegerConstant , StubApiCInclude , StubApiCFunction , StubApiCFile .

###

StubApiCFile -- set file name for plugin API

##### Standard library

##### Calling format:

    StubApiCFile(basename)

##### Parameters:

`basename` -- name for the generation of the stub file

##### Description:

Generate the C++ stub file, "basename.cc", and a documentation file named "basename.description". The descriptions are automatically generated while adding functions and constants to the stub.

##### See also:

StubApiCStart , StubApiCShortIntegerConstant , StubApiCInclude , StubApiCFunction , StubApiCSetEnv .

###

StubApiCStruct -- declare C struct in plugin

##### Standard library

##### Calling format:

    StubApiCStruct(name)
    StubApiCStruct(name,freefunction)

##### Parameters:

`name` -- name of structure

`freefunction` -- function that can be called to clean up the object

##### Description:

`StubApiCStruct` declares a `struct` in a specific library. The name should be followed by an asterisk (clearly showing that it is a pointer). After that, in the stub API definition, this type can be used as argument or return type to functions to the library.

By default the struct will be deleted from memory with a normal call to `free(...)`. This can be overridden with a function given as second argument, freefunction. This is needed in the case where there are additional operations that need to be performed in order to delete the object from memory.

##### Examples:

In a library header file, define:

    typedef struct SomeStruct
    {
      int a;
      int b;
    } SomeStruct;

Then in the stub file you can declare this struct by calling:

    StubApiCStruct("SomeStruct*")

##### See also:

StubApiCFunction .