Re: [Chicken-users] srfi-18 and dynamic wind problem

[Alaric Snell-Pym]

On 6 Apr 2008, at 5:41 am, Jim Ursetto wrote:
> I'm seeing some odd behavior when using dynamic-wind within a thread.
> If an error occurs during the thunk, the 'after' portion is never
> called nor are any subsequent statements. thread-join! then throws
> an exception.


I was also worrying why the example from srfi-18 didn't work, which
would seem related:

> #;1>     (with-output-to-file
> --->      "foo"
> --->      (lambda ()
> --->        (let ((k (call-with-current-continuation
> --->                  (lambda (exit)
> --->                    (with-output-to-file
> --->                     "bar"
> --->                     (lambda ()
> --->                       (dynamic-wind
> --->                        (lambda () (write '(b1)))
> --->                        (lambda ()
> --->                          (let ((x (call-with-current-continuation
> --->                                    (lambda (cont) (exit cont)))))
> --->                            (write '(t1))
> --->                            x))
> --->                        (lambda () (write '(a1))))))))))
> --->          (if k
> --->              (dynamic-wind
> --->               (lambda () (write '(b2)))
> --->               (lambda ()
> --->                 (with-output-to-file
> --->                  "baz"
> --->                  (lambda ()
> --->                    (write '(t2))
> --->                    ; go back inside (with-output-to-file
> "bar" ...)
> --->                    (k #f))))
> --->               (lambda () (write '(a2))))))))
> #;2>
> alaric$ ls
> bar baz foo
> alaricn$ cat foo
> alaric$ cat bar
> (b1)(a1)(b2)
> alaric$ cat baz
> (t2)(a2)(b1)(t1)(a1)

(b1) and (a1) are written to bar, but then the current output port is
still to bar when (b2) is written, outside of the scope of the with-
output-to-file "bar"; it should go to foo. Likewise, (a2) gets
written to baz and not to foo, and (b1)(t1)(a1) goes to baz and not bar.

ABS

--
Alaric Snell-Pym
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