Re: Closure?

[Kjetil S. Matheussen]

Ludovic Court?s:
> "Maciek Godek" <address@hidden> writes:
>
> > I've been wondering if there's any way to recall
> > (or get inside) an environment of a closure (= to
> > directly access variables bound to a closure)
>
> Yes, with `the-environment':
>
>  guile> ((lambda (a b) (the-environment)) 2 3)
>  (((a b) 2 3) #<eval-closure b7c6dcf8>)
>
> But don't do that, since the representation of environments could
> eventually change.

Please don't change it. :-)
It's one of those things which makes Guile special.



Maciek Godek:
> Don't worry, I won't :)
> Now I only know how to obtain environment of a closure,
> but I still don't know how to get inside and modify it (I'm
> lacking this `with' I wrote about).

The function "local-eval" is probably what you want.

I use local-eval a lot, it's one of the really really
nice features provided by Guile:


(define-macro (with env . code)
  `(local-eval (quote (begin ,@code)) ,env))


(define ++
  (let ((c 0))
    (c-display "env" (the-environment))
    (lambda()
      (set! c (1+ c)) c)))

(++)
=> 1
(with (procedure-environment ++) (set! c 20))

(++)
=> 20