Macro

Summary

Defines a Lisp function which can be called from a foreign language.

Package

fli

Signature

define-foreign-callable ( foreign-name &key encode language result-type result-pointer no-check calling-convention ) ( {args }*) &body body => lisp-name

args ::= { arg-name } | ( arg-name arg-type )

Arguments

foreign-name

A string or symbol naming the Lisp callable function created.

encode

By default, LispWorks performs automatic name encoding to translate foreign-name

If you want to explicitly specify an encoding, the encode option can be one of the following:

:source tells LispWorks that foreign-name is the function name to call from the foreign source code. This is the default value of encoding .

:object tells LispWorks that foreign-name is the literal name to be called in the foreign object code.

:lisp tells LispWorks that if foreign-name is a Lisp symbol, it must be translated and encoded.

:dbcs adds a suffix onto the function name which will automatically change depending on whether Lisp image is started up in the Windows NT or Windows 95 operating system. The suffix is " A " for Windows 95 and " W " for Windows NT.

language

The language in which the foreign calling code is written. The default is :c .

result-type

The FLI type of the Lisp foreign callable function's return value which is passed back to the calling code.

result-pointer

A variable which will be bound to a foreign pointer into which the result should be written when the result-type is an aggregate type.

no-check

If nil , the result of the foreign callable function, produced by body , is checked to see if matches the result-type , and an error is raised if they do not match. Setting no-check to t overrides this check.

calling-convention

Specifies the calling convention used.

:stdcall is the calling convention used to call Win32 API functions and matches the C declarator "__stdcall" . This is the default on Windows.

:cdecl is the default calling convention for C/C++ programs and matches the C declarator "__cdecl" . This is the default on Unix/Linux. There is no calling convention issue on Macintosh.

args

The arguments of the Lisp foreign callable function. Each argument can consist either of an arg-name , in which case LispWorks assumes it is an :int , or an arg-name and an arg-type , which is an FLI type.

body

A list of forms which make up the Lisp foreign callable function.

Values

lisp-name

A string or symbol naming the Lisp callable function created.

Description

The macro define-foreign-callable defines a Lisp function that can be called from a foreign language, for example from a C function. When the Lisp function is called, data passed to it is converted to the appropriate FLI representation, which is translated to an appropriate Lisp representation for the Lisp part of the function. Once the callable function exits, any return values are converted back into an FLI format to be passed back to the calling language.

When the result-type is a aggregate type, an additional variable is bound in the body to allow the value of the function to be returned (the value returned by the body is ignored). This argument is named after the result-pointer argument or is named result-pointer in the current package if unspecifed. While the body is executing, the variable will be bound to a foreign pointer that points to an object of the type result-type . The body must set the slots in this foreign object in order for the value to be returned to the caller.

To make a function pointer referencing a foreign callable Foo , use:

(make-pointer :symbol-name "Foo")

Example

The following example demonstrates the use of foreign callable. A foreign callable function, square , is defined, which takes an integer as its argument, and returns the square of the integer.

(fli:define-foreign-callable 

  ("square" :result-type :int)

  ((arg-1 :int)) (* arg-1 arg-1))

The foreign callable function, square , can now be called from a foreign language. We can mimic a foreign call by using the define-foreign-function macro to define an FLI function to call square .

(fli:define-foreign-function (call-two "square")

  ((in-arg :int)) :result-type :int)

The call-two function can now be used to call square . The next command is an example of this.

(call-two 9)

This last example shows how the address of a foreign callable can be passed via a pointer object. The foreign library in this example is libgsl:

(fli:define-foreign-callable ("gsl-error-handler")

    ((reason (:reference-return :ef-mb-string))

     (file (:reference-return :ef-mb-string))

     (lineno :integer)

     (gsl-errno :integer))

  (error 

   "Error number ~a inside GSL [file: ~a, lineno ~a]: ~a"

   gsl-errno file lineno reason))

(fli:define-foreign-function gsl-set-error-handler 

    ((func :pointer))

  :result-type :pointer)

To set the error handler, you would do:

(gsl-set-error-handler 

 (fli:make-pointer :symbol-name "gsl-error-handler"))

See also

define-foreign-function
define-foreign-variable
make-pointer