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Re: Closure?

From: Kjetil S. Matheussen
Subject: Re: Closure?
Date: Fri, 11 Jul 2008 19:42:40 +0200 (CEST)

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))
      (set! c (1+ c)) c)))

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

=> 20

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