Re: Jim's wish list: gd library interface

[mike@olan.com (Michael N. Livshin)]

Todd Larason <jtl@molehill.org> writes:

[ snip ]

>   R5RS features: We use R5RS multi-value return forms: VALUES,
>                  CALL-WITH-VALUES, and RECEIVE.
> 
> I can't find RECEIVE in r5rs;

It's not there.

> Guile's (ice-9 syncase) has call-with-values and values procedures defined
> that look like they might do the right thing; what I don't understand is
> how to use them.  They're (define)d, not (define-public)d, so as far as
> I understand, they can only be used from the syncase module; they're not
> used there though, so I expect I'm missing something in the guile
> module system.  Anyone have some pointers?

There really should be one definition of the VALUES stuff, and (for now at least)
it should be in ice-9 or somesuch.

I suggest the following code.  It's by Will Clinger, and extended by me to
redefine call-with-current-continuation in R5RS-compatible way (so that
escape procedures take any number of parameters).

------------------->8 cut cut 8<----------------------------

(define values #f)
(define call-with-values #f)

(let* ((apply apply)
       (*multiple-values* (list '*multiple-values*))
       (*values0* (list *multiple-values*))
       (call/cc call-with-current-continuation))
  (set! values
        (lambda vals
          (cond ((null? vals) *values0*)
                ((null? (cdr vals)) (car vals))
                (else (cons *multiple-values* vals)))))
  (set! call-with-values
        (lambda (producer consumer)
          (let ((vals (producer)))
            (if (and (pair? vals)
                     (eq? (car vals) *multiple-values*))
                (apply consumer (cdr vals))
                (consumer vals)))))
  (set! call-with-current-continuation
	(lambda (f)
	  (call/cc
	   (lambda (c)
	     (f (lambda args (c (apply values args)))))))))

(provide 'values)

------------------->8 cut cut 8<----------------------------