[Emacs-bug-tracker] bug#748: closed (Elisp: lexical-let and cyclic structures)

[GNU bug Tracking System]

Your message dated Sat, 09 Jul 2011 13:51:43 -0400
with message-id <address@hidden>
and subject line Re: bug#748: Elisp: lexical-let and cyclic structures
has caused the GNU bug report #748,
regarding Elisp: lexical-let and cyclic structures
to be marked as done.

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-- 
748: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=748
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> --- Begin Message ---
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> Subject: 
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> Elisp: lexical-let and cyclic structures
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> Date: 
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> Wed, 20 Aug 2008 15:57:16 +0200
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> When using the reader constructs `#N=' and `#N#' for cyclic
> structures, lexical-let sometimes produces errors which don't occur
> with let.
>
> Example: Eval the following:
>
> (defun f (start)
>   (lexical-let (start start)         ;; return a closure
>     #1=(lambda (x) (if (= x start) x
>                      (+ x (#1# (1- x)))))))
>
> Then evaluating f ends with an error:
>
>    (f 3)
>
>     "Variable binding depth exceeds max-specpdl-size"
>
>
> The problem also occurs without lambdas. Examples:
>
>    (let         () '#1=(#1#))               ;; ==> (#0)
>    (lexical-let () '#1=(#1#))               ;;  Error
>    (let ((x '#1=(#1#))) (lexical-let () x)) ;; ==> (#0)
>    `#1=(#1#)                                ;;  Error
>
>
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> --- End Message ---
> --- Begin Message ---
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>
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> Subject: 
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> Re: bug#748: Elisp: lexical-let and cyclic structures
>
>
>
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> Date: 
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> Sat, 09 Jul 2011 13:51:43 -0400
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> User-agent: 
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> Gnus (www.gnus.org), GNU Emacs (www.gnu.org/software/emacs/)
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>
> I don't see a need to keep open this particular report, which was marked
> "wontfix" some time ago.
>
> Stefan Monnier wrote:
>
> > Most programming languages do not accept infinite programs.  Elisp is
> > no exception.  The fact that you can build cyclic abstract syntax trees
> > and that they sometimes get evaluated correctly is just an accident.
> >
> > I.e. if it hurts, don't do it.
>
>
> --- End Message ---