[iterate-devel] Iterate broken on ACL 7.0 beta?

[Andreas Fuchs]

Today, Arthur Lemmens <alemmens at xs4all.nl> wrote:
> I just downloaded iterate 1.0.9 from common-lisp.net and tried
> it with ACL 7.0 beta.
>
> Unfortunately, I get a stack overflow error (see the backtrace
> below) when I do the following:
[snip & paste]
> 6: (MACROEXPAND-1 (COND ((>= VALUE 10) NIL (COLLECT (CONS KEY (NEXT I))))) NIL)
> 7: (MACROEXPAND (COND ((>= VALUE 10) NIL (COLLECT (CONS KEY (NEXT I))))) NIL)
> 8: (WALK (COND ((>= VALUE 10) NIL (COLLECT (CONS KEY (NEXT I))))) NIL)
> 9: (WALK (COND ((>= VALUE 10) NIL (COLLECT (CONS KEY (NEXT I))))) NIL)
> 10: (WALK (COND ((>= VALUE 10) NIL (COLLECT (CONS KEY (NEXT I))))) NIL)

Strange. I get the expected result when I try it with allegro 6.2. I
suspect that the COND form that appears so often in the backtrace is
not macroexpanded correctly (or treated as a special form by allegro7
again - there is a comment indicating that in the "old" iterate
distribution).

I have a possible fix ready, but to confirm it's correct (or utterly
wrong), I'll need to know which values

(macroexpand (cond ((>= value 10) nil (collect (cons key (next i))))) nil)

returns on your allegro 7 installation. 

Also, you are welcome to try the patch I suspect will fix the problem:

--- orig/iterate.lisp
+++ mod/iterate.lisp
@@ -628,7 +628,8 @@
       ;; functions; and, by personal preference, special operators
       ;; should be expanded before iterate clauses.
 
-      ((macro-function (car form) *env*)
+      ((and (macro-function (car form) *env*)
+            (nth-value 1 (macroexpand form *env*)))
        (walk (macroexpand form *env*)))
       ((special-form? (car form))
        (walk-special-form form))


> This is not critical for me (I'll just use an older version of
> iterate that I've been using for the last 4 years and that has
> no problems with your example or with my programs in general),
> but I thought you might want to know this.
>
> Sorry that I don't come with a fix, but I don't have the time for
> debugging this right now.

No problem; your description has given me a good idea as to where the
bug is. I hope you find the time to test the fix, though. (-:

Thanks for the report! Cheers,
-- 
Andreas Fuchs, <asf at boinkor.net>, asf at jabber.at, antifuchs