Foreign Types ​

From Scheme’s perspective, foreign pointers are shards of chaos. The user can create a foreign pointer for any address, and do with it what they will. The only thing that lends a sense of order to the whole is a shared hallucination that certain storage locations have certain types. When making Scheme wrappers for foreign interfaces, we hide the madness by explicitly representing the the data types of parameters and fields.

These “foreign type values” may be constructed using the constants and procedures from the (system foreign) module, which may be loaded like this:

emacs-lisp
(use-modules (system foreign))

(system foreign) exports a number of values expressing the basic C types.

Scheme Variable: int8 ​

Scheme Variable: uint8 ​

Scheme Variable: uint16 ​

Scheme Variable: int16 ​

Scheme Variable: uint32 ​

Scheme Variable: int32 ​

Scheme Variable: uint64 ​

Scheme Variable: int64 ​

Scheme Variable: float ​

Scheme Variable: double ​

Scheme Variable: complex-double ​

Scheme Variable: complex-float ​

These values represent the C numeric types of the specified sizes and signednesses. complex-float and complex-double stand for C99 float _Complex and double _Complex respectively.

In addition there are some convenience bindings for indicating types of platform-dependent size.

Scheme Variable: int ​

Scheme Variable: unsigned-int ​

Scheme Variable: long ​

Scheme Variable: unsigned-long ​

Scheme Variable: short ​

Scheme Variable: unsigned-short ​

Scheme Variable: size_t ​

Scheme Variable: ssize_t ​

Scheme Variable: ptrdiff_t ​

Scheme Variable: intptr_t ​

Scheme Variable: uintptr_t ​

Values exported by the (system foreign) module, representing C numeric types. For example, long may be equal? to int64 on a 64-bit platform.

Scheme Variable: void ​

The void type. It can be used as the first argument to pointer->procedure to wrap a C function that returns nothing.

In addition, the symbol * is used by convention to denote pointer types. Procedures detailed in the following sections, such as pointer->procedure, accept it as a type descriptor.