Foreign Library

The (cyclone foreign) provides a convenient interface for integrating with C code. It is based in concept on the (chicken foreign) module from CHICKEN Scheme. Similarly to that module, this library manipulates the C code directly before it is compiled to a native binary. It is not possible to call these forms at runtime.

Overview

• c-code
• c-value
• c-define
• c-define-type

c-code

Syntax

(c-code CODE ...)

Insert C code directly into the compiled program. Each CODE parameter must be a string containing C code.

c-value

Syntax

(c-value CODE TYPE)

Generate code that takes the C code specified by the string CODE and converts it to a Scheme object of type TYPE.

c-define

Syntax

(c-define SCM-FUNC RETURN-TYPE C-FUNC TYPE ...)

Define a Scheme function SCM-FUNC returning an object of type RETURN-TYPE. The function will call C function specified by the string C-FUNC passed parameters of type specified by any TYPE arguments.

For example, to define a function that calls strlen:

(c-define scm-strlen int "strlen" string)

Note that these definitions are introduced at the top-level.

c-define-type

Syntax

(c-define-type NAME TYPE (ARG-CONVERT (RET-CONVERT)))

Define a custom type with symbol NAME that is an alias of type TYPE. It is also possible to specify conversion functions ARG-CONVERT and RET-CONVERT to convert to/from this custom type.

EG, to define a type that consists of integers in Scheme and strings in C:

(c-define-type string-as-integer string number->string string->number)

Type Specifiers

The following built-in specifiers may be used as a TYPE for forms in this module.

Useful notes:

• Use opaque if you need to handle any kind of C pointer.
• Use string to handle C const char* (symbol is strictly used to represent Scheme symbols).

• thread-data is a special type used to pass the current thread’s gc_thread_data instance to a C function. These objects are passed implicitly when making a Scheme function call. For example:

   (c-define sub-big-nums bignum "sub_big_nums" thread-data bignum bignum)
   (sub-big-nums 999999999999999999999999 222222222222222222222222))