Re: [Chicken-users] Accessing C macro definitions from scheme?

[felix]

On Sat, 16 Aug 2003 10:08:03 -0700, Burton Samograd <address@hidden> 
wrote:

> Hi,
>
> I'm trying to write a simple interface wrapper for a small library I
> would like to use and I can seem to be able to acess constant #define's
> in a way that seems reasonable.  What I'm looking for is something
> like this:
>
> -----------------------------------------------------------------------
>
> /* header.h */
> #define MY_DEFINED_VALUE (0L)
>
> -----------------------------------------------------------------------
>
> ;;; wrapper.scm
> (declare
> (export
> my-defined-value))
>
> ; include the header so we can get at MY_DEFINED_VALUE
> (declare (foreign-declare "#include \"header.h\""))
>
> (define my-defined-value
> ( +++ WHAT GOES HERE TO GET THE VALUE OF MY_DEFINED_VALUE? ***))

Try:

(define-foreign-variable _my-defined-value int "MY_DEFINED_VALUE")
(define my-defined-value _my-defined-value)

The foreign variable defined `define-foreign-variable' is only visible
in the currently compiled file, so the second definition is needed.
Another approach would be something like:

(define-macro (define-exported-foreign-variable name type text)
 (let ([tmp (gensym)])
   `(begin
      (define-foreign-variable ,tmp ,type ,text)
      (define ,name ,tmp) ) ) )

(define-exported-foreign-variable my-defined-value int "MY_DEFINED_VALUE")

[Courtesy of Peter Wang]

This doesn't work for mutable variables. But a "parameter"-like approach
would work for that, like:

(define-macro (define-exported-foreign-variable name type text)
 (let ([tmp (gensym)])
   `(begin
      (define-foreign-variable ,tmp ,type ,text)
      ,(if (pair? name)
         `(define (,name . val) (if (pair? val) (set! ,tmp val) ,tmp) )
         `(define ,name ,tmp) ) ) ) )

So for example,

(declare (foreign-declare "int foo;"))

(define-exported-foreign-variable (foo) int "foo")

(foo 33)
(foo)  ; ==> 33


> -----------------------------------------------------------------------
>
> I would like to be able to compile the wrapper.scm using 'csc -s
> wrapper.scm' to produce wrapper.so, be able to load it into csi with a
> (require 'wrapper) and then be able to access my-defined-value, but so
> far I haven't be able to get it to work.
>
> ##core#inline looked promising, but also didn't seem to do what I
> wanted unless I defined a macro that took a parameter which returned
> the define, such as this:
>
> (declare (foreign-declare "#define CONST(arg) arg"))
> (define my-defined-value (##core#inline CONST MY_DEFINED_VALUE))

Yep, ##core#inline is really more a tool for hacking internals.


cheers,
felix