On Fri, 11 Jul 2008, Maciek Godek wrote:
Kjetil S. Matheussen:
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)))
I don't actually get the line with c-display.
Does it require any additional module?
'Cause it ain' workin' for me.
(and besides what does it do?
the remaining part works fine)
Just ignore that one. c-display is just a debugging
function I forgot to remove. :-)
(++)
=> 1
(with (procedure-environment ++) (set! c 20))
(++)
=> 20
I'm really impressed :) Great respect!
I only wonder if there's a way to add a new
variable to an existing closure, or to delete one.
(not that I need it right now; but I imagine that
it can be implemented quite easily and efficiently
in C if the notion of closure is well-defined and
explicit)
Adding is easy:
(define (add-var-to-environment env name val)
(local-eval `(let ((,name ,val)) (the-environment))
env))
(define env (add-var-to-environment (the-environment) 'a 50))
(local-eval 'a env)
=> 50
I don't know if there's possible to delete a variable
in a clean way.
