Re: Newbie question on writing bindings.

[Neil Jerram]

>>>>> "Martin" == Martin Grabmueller <address@hidden> writes:

    >> From: Joel Smith <address@hidden> Date: Sat, 14 Apr 2001
    >> 21:59:27 +0000 (GMT)
    >> 
    >> How do I write bindings for such functions? I thought about
    >> passing the various values as a list but that does not seem
    >> like the Right Thing to me. I also thought of using keyword
    >> arguments like this:
    >> 
    >> (baz #:foo #t :#bar #t)
    >> 
    >> But I don't know how to write a C routine to handle keyword
    >> arguments. I have looked at other guile code to see if anyone
    >> else has solved this problem but I could not find any examples
    >> of it. Surely I can't be the only person who wants to do this?
    >> ;-) Any help would be much appreciated!

    Martin> I haven't tried to use keywords in Guile extensions yet,
    Martin> but I think you would have to

    Martin> 1. Define your primitive written in C to accept
    Martin> arbitrarily many arguments. [...]

    Martin> But personally, I like it better to write the primitive
    Martin> `baz' in a way that it can be called like

    Martin> (baz 'foo 'bar) [...]

Also, as a general idea, consider defining your C primitive so that
it's easy to write in C, and then write a Scheme level wrapper
function with an interface that is convenient to call.  For example:

SCM scm_baz_raw(SCM flags) /* flags is expected to be an integer */
{
  int cflags;
  SCM_VALIDATE_INUM_COPY (SCM_ARG1, flags, cflags);
  baz_internal (cflags);
  return SCM_UNSPECIFIED;
}

(define (baz . symbols)
  (let ((accum 0)
        (alist '((foo . 1)
                 (bar . 2)
                 (gan . 4)
                 ...)))
    (for-each (lambda (sym)
                (set! accum (logior accum (assq-ref alist sym))))
              symbols)
    (baz-raw accum)))

In other words, it much easier to do nice interfacey stuff in Scheme
than in C.

Regards,
        Neil

PS. Totally untested, of course.