Re: The GIMP! By gum, I forgot all about it!

[Lauri Alanko <la@iki.fi>]

On Thu, Oct 29, 1998 at 11:10:34AM -0500, it occurred to Maciej Stachowiak to write:
> 
> scott@poverty.bloomington.in.us writes:
> > Last I heard Lauri was swearing at how hard it was to emulate SIOD's
> > braindead set! semantics in guile.
> 
> What does SIOD do with set! that's so unusual?

;; SIOD's set! is really screwed up. If the variable being set is
;; unbound, it is bound at the top level. Otherwise it is reset. So we
;; have to find out if a variable is bound in a _local_ environment.. thus
;; we create the syntax manually. Also, SIOD set! returns the new value.

;; There would be no prob otherwise, but all scripts use these "features"..

(define set! 
  ; we memoize the correct place for the variable..
  (procedure->memoizing-macro
   (lambda (exp env)
     (define variable (cadr exp))
     (define value (caddr exp))
     `(begin 
        (,@(let loop ((e env))
             (define frame (car e))
             (cond ((procedure? frame)
                    ; here we create the top level binding
                    `(',variable-set! ',(frame variable #t)))
                   ((eq? (car frame) variable)
                    `(set-cdr! ',frame))
                   ((and (list? (car frame)) (list-index (car frame) variable))
                    => (lambda (i)
                         `(',set-car! ',(list-tail (cdr frame) i))))
                   (else (loop (cdr e)))))
         ,value)
        ,variable))))


Yes, this is hyper-kludgy. I don't know if this even works with latest
guile. Cleaner solutions welcome. :)


Lauri Alanko
la@iki.fi