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[Chicken-users] problem with callbacks

From: Daniel B. Faken
Subject: [Chicken-users] problem with callbacks
Date: Thu, 22 Jan 2004 09:34:44 -0500 (EST)

Hello all,

  My 'foreign-callback-wrapper' doesn't seem to be capturing the local 
environment - is this correct?  (please pardon me if this is obvious - I'm 
a scheme newbie)

An example:
(declare (uses extras))

(let ((foo (make-hash-table)))

__callback void test_fn(int val)
  extern void scm_callback2(int);

  (print "hello!")
  (clear-hash-table! foo)

  (define-external (scm_callback (int val)) void
    (print "callback-val is " val)
    (print "in callback: foo is " foo)

  (define callback2 
    (foreign-callback-wrapper void "scm_callback2" 
    (int) (lambda (x) (print "callback-val is " x)
                  (print "in callback: foo is " foo))))

  (print "foo is " foo)
  (test_fn 50)
produces this output:
gloriot2:~/cr/spu/viewpoint/htcam%csc tst.scm
foo is #<hash-table>
callback-val is 50
Error: unprintable non-immediate object encountered

tst.scm: 3    make-hash-table
tst.scm: 13   print
tst.scm: 14   clear-hash-table!
tst.scm: 27   print
tst.scm: 28   test_fn
tst.scm: 23   print
tst.scm: 24   print
in callback: foo is gloriot2:~/cr/spu/viewpoint/htcam%

(my actual program is of course more complicated)

This fails for 'test_fn()' calling either scm_callback()
or scm_callback2().

thanks for any help!

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