Re: [Chicken-users] problem with callbacks

[Felix Winkelmann]

Am Thu, 22 Jan 2004 09:34:44 -0500 (EST) hat Daniel B. Faken 
<address@hidden> geschrieben:

> Hello all,
>
>   My 'foreign-callback-wrapper' doesn't seem to be capturing the local
> environment - is this correct?

That is correct. Both `foreign-callback-wrapper' and `define-external'
(which expands into the former) do not capture the lexical environment.
The problem is that C invokes the callback directly via it's function
address, to pass the lexical environment and extra argument would have
to be passed. A workaround is to call your target procedure indirectly:

(define bar #f)

(let ([foo 99])
  (set! bar (lambda () (print foo))) )

(define-external (cb) void
  (bar) )

#>!
__callback void ccb() { extern void cb(); cb(); }
<#

(ccb)


cheers,
felix