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Wrapping Another Simple C Type

If you want to wrap a simple C type which is does not fit in any of the categories above, then G-Wrap provides a simple high-level function for that purpose.

— method: wrap-simple-type! (wrapset . <gw-wrapset>) . args

Add the type described by args to the list of types to be wrapped by wrapset. The arguments in args must contain the following named parameters:

#:name
a symbol that is the name for this wrapped type as used within the G-Wrap framework;
#:c-type-name
a string that is the C name of this enumerate type;
#:type-check
a list representing C expression that returns true if the given Scheme value's type is this type; this list may contain strings (representing part of the C expression) and the scm-var symbol which will be expanded to the name of the C variable that holds the Scheme value;
#:ffspec
a symbol representing the libffi type name that describes this type best; it may be, for instance, pointer for pointer types, long for long integers, etc.; in other words, this is meant to provide run-time type information, as described in See Wrapped Types.
#:unwrap
a list representing a C statement that assigns (and converts) the value of a C variable holding a Scheme value to a C variable holding the corresponding C value; as for #:type-check, this list may only contain strings and symbols; the symbol scm-var will be expanded to the name of the C variable that holds the Scheme value, while the symbol c-var will be expanded to the C variables that will hold the corresponding C value;
#:wrap
a list representing a C statement that assigns (and converts) the value of a C variable holding a C value to a C variable holding the corresponding Scheme value; the content and interpretation of the list as the same as for #:unwrap;
#:description
an optional description of this type.

As an example, the simple scm wrapped type which lets the user wrap C functions that take or return raw SCM objects (see see Guile's SCM type, for a description of Guile's C type for Scheme objects) is defined as follows: 

     (wrap-simple-type! wrapset
                        #:name 'scm
                        #:c-type-name "SCM"
                        #:type-check '("1") ;; any Scheme value is correct
                        #:ffspec 'pointer
                        ;; no conversion is needed
                        #:unwrap '(c-var " = " scm-var ";\n")
                        #:wrap '(scm-var " = " c-var ";\n"))

If wrap-simple-type! is still not good enough for what you want to do, then you may have a look at the details of G-Wrap's code generation interface, See G-Wrap's Code Generation API.