![]() ![]() ![]() 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. foreign-lambda* (foreign-lambda* RETURNTYPE ((ARGTYPE VARIABLE). NAME specifies the name of the external procedure and should be a string or a symbol. This form can be used in the position of an ordinary lambda expression. Represents a binding to an external routine. foreign-lambda (foreign-lambda RETURNTYPE NAME ARGTYPE. Changing the second line to (define-external x double 0.5) will work (and the value 0.5 will be printed). 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). For example, the following code: ( import ( chicken foreign)) ( define-foreign-variable x double "var_x") ( print x) To actually create Scheme variables visible from C, use define-external (see the Manual section on Callbacks). 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. If no assignments are performed, then STRING doesn't even have to specify an lvalue. Note that STRING can name an arbitrary C expression. This foreign variable can only be accessed in the current compilation unit, but the name can be lexically shadowed. All references and assignments (via set!) are modified to correctly convert values between Scheme and C representation. If STRING is not given, then the variable name NAME will be converted to a string and used instead. STRING should be the real name of a foreign variable or parameterless macro. define-foreign-variable (define-foreign-variable NAME TYPE )ĭefines a foreign variable of name NAME (a symbol). This is basically equivalent to ( foreign-value "sizeof(TYPE)" size_t)īut also handles user-defined types and allows "TYPE" to be a string, which will be given literally to the sizeof operator. Returns the size of the storage required to hold values of the given foreign type TYPE. foreign-type-size (foreign-type-size TYPE) ( foreign-lambda char-vector "memset" char-vector char int)) ( memset '# ( #_ #_ #_) #\X 3) => # ( #\X #\X #\X)įoreign 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. ( foreign-lambda int "strlen" char-vector)) ( strlen '# ( #\a #\b #\c)) => 3 ( compose list->string vector->list) ( compose list->vector string->list)) ( define strlen 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 The namespace of foreign type specifiers is separate from the normal Scheme namespace. TYPE may be a type-specifier or a string naming a C type. define-foreign-type (define-foreign-type NAME TYPE ])ĭefines an alias for TYPE with the name NAME (a symbol). Include given strings verbatim into header of generated file. ( print ( foreign-value "my_version_string" c-string)) foreign-declare (foreign-declare STRING. foreign-value (foreign-value CODE TYPE)Įvaluates 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. ( foreign-code "doSomeInitStuff() ") => #Ĭode wrapped inside foreign-code may not invoke callbacks into Scheme. , which should be a sequence of C statements, which are executed and return an unspecified result. )Įxecutes the embedded C/C++ code STRING. Accessing external objects foreign-code (foreign-code STRING. Several special forms of this interface refer to foreign type specifiers, consult the relevant chapter of this manual for more information. It is not binary, as in many other Scheme implementations. Note that this interface is source-based, since CHICKEN translates Scheme code to C. This module provides a foreign function interface to access externally defined functions and variables in C-compatible languages, as well as operating-system specific functionality. ![]()
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