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
(use-modules (system foreign))
(system foreign) exports a number of values expressing the basic
These values represent the C numeric types of the specified sizes and
complex-double stand for
float _Complex and
double _Complex respecively.
In addition there are some convenience bindings for indicating types of platform-dependent size.
Values exported by the
(system foreign) module, representing C
numeric types. For example,
long may be
int64 on a 64-bit platform.
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.