You are looking at historical revision 17774 of this page. It may differ significantly from its current revision.
Accessing external objects
foreign-code[syntax] (foreign-code STRING ...)
Executes the embedded C/C++ code STRING ..., which should be a sequence of C statements, which are executed and return an unspecified result.
(foreign-code "doSomeInitStuff();") => #<unspecified>
Code wrapped inside foreign-code may not invoke callbacks into Scheme.
foreign-value[syntax] (foreign-value CODE TYPE)
Evaluates the embedded C/C++ expression CODE (which may be a string or symbol), returning a value of type given in the foreign-type specifier TYPE.
(print (foreign-value "my_version_string" c-string))
foreign-declare[syntax] (foreign-declare STRING ...)
Include given strings verbatim into header of generated file.
define-foreign-type[syntax] (define-foreign-type NAME TYPE [ARGCONVERT [RETCONVERT]])
Defines an alias for TYPE with the name NAME (a symbol). TYPE may be a type-specifier or a string naming a C type. The namespace of foreign type specifiers is separate from the normal Scheme namespace. The optional arguments ARGCONVERT and RETCONVERT should evaluate to procedures that map argument- and result-values to a value that can be transformed to TYPE:
(define-foreign-type char-vector nonnull-c-string (compose list->string vector->list) (compose list->vector string->list) ) (define strlen (foreign-lambda int "strlen" char-vector) ) (strlen '#(#\a #\b #\c)) ==> 3 (define memset (foreign-lambda char-vector "memset" char-vector char int) ) (memset '#(#_ #_ #_) #\X 3) ==> #(#\X #\X #\X)
Foreign type-definitions are only visible in the compilation-unit in which they are defined, so use include to use the same definitions in multiple files.
define-foreign-variable[syntax] (define-foreign-variable NAME TYPE [STRING])
Defines a foreign variable of name NAME (a symbol). STRING should be the real name of a foreign variable or parameterless macro. If STRING is not given, then the variable name NAME will be converted to a string and used instead. All references and assignments (via set!) are modified to correctly convert values between Scheme and C representation. This foreign variable can only be accessed in the current compilation unit, but the name can be lexically shadowed. Note that STRING can name an arbitrary C expression. If no assignments are performed, then STRING doesn't even have to specify an lvalue. See that define-foreign-variable will not generate C declarations or memory allocation code; use it to include references to variables in external C code. To actually create Scheme variables visible from C, use define-external (see the Manual section on Callbacks). For example, the following code:
(import foreign) (define-foreign-variable x double "var_x") (print x)
will not work, because a reference to var_x will be inserted in the C code, but no declaration will be included (this can be easily verified by translating the program into C with csc -t program.scm).
foreign-lambda[syntax] (foreign-lambda RETURNTYPE NAME ARGTYPE ...)
Represents a binding to an external routine. This form can be used in the position of an ordinary lambda expression. NAME specifies the name of the external procedure and should be a string or a symbol.
foreign-lambda*[syntax] (foreign-lambda* RETURNTYPE ((ARGTYPE VARIABLE) ...) STRING ...)
Similar to foreign-lambda, but instead of generating code to call an external function, the body of the C procedure is directly given in STRING ...:
(define my-strlen (foreign-lambda* int ((c-string str)) "int n = 0; while(*(str++)) ++n; C_return(n);") ) (my-strlen "one two three") ==> 13
For obscure technical reasons you should use the C_return macro instead of the normal return statement to return a result from the foreign lambda body as some cleanup code has to be run before execution commences in the calling code.
foreign-safe-lambda[syntax] (foreign-safe-lambda RETURNTYPE NAME ARGTYPE ...)
This is similar to foreign-lambda, but also allows the called function to call Scheme functions and allocate Scheme data-objects. See Callbacks.
foreign-safe-lambda*[syntax] (foreign-safe-lambda* RETURNTYPE ((ARGTYPE VARIABLE)...) STRING ...)
This is similar to foreign-lambda*, but also allows the called function to call Scheme functions and allocate Scheme data-objects. See Callbacks.
foreign-primitive[syntax] (foreign-primitive [RETURNTYPE] ((ARGTYPE VARIABLE) ...) STRING ...)
This is also similar to foreign-lambda* but the code will be executed in a primitive CPS context, which means it will not actually return, but call its continuation on exit. This means that code inside this form may allocate Scheme data on the C stack (the nursery) with C_alloc (see below). If the RETURNTYPE is omitted it defaults to void. You can return multiple values inside the body of the foreign-primitive form by calling this C function:
C_values(N + 2, C_SCHEME_UNDEFINED, C_k, X1, ...)
where N is the number of values to be returned, and X1, ... are the results, which should be Scheme data objects. When returning multiple values, the return-type should be omitted.
Next: Foreign type specifiers