GNU bug report logs - #70597
Problem in pcase-let?

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#70597: closed (Problem in pcase-let?)
Date: Sat, 04 May 2024 11:37:02 +0000

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Your message dated Sat, 04 May 2024 14:35:43 +0300
with message-id <861q6hhks0.fsf <at> gnu.org>
and subject line Re: bug#70597: Problem in pcase-let?
has caused the debbugs.gnu.org bug report #70597,
regarding Problem in pcase-let?
to be marked as done.

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help-debbugs <at> gnu.org.)


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70597: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=70597
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From: Marco Antoniotti <marcoxa <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Problem in pcase-let?
Date: Fri, 26 Apr 2024 20:00:02 +0200

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Hi

This is for GNU Emacs 29.2 (build 2, x86_64-w64-mingw32) of 2024-02-01
running on Windows 11.

I just noticed the following with pcase-let and pcase.  I believe this is a
problem with pcase-let.  The following is a IELM transcript.  The second
plet-case should, IMHO, fail.

ELISP> (pcase-let ((`(let ,bs (*when *,c . ,r)) '(let ((foo 42)) (*when *1
2 3))))
         (list 'bs bs 'c c 'r r))
(bs
 ((foo 42))
 c 1 r
 (2 3))

ELISP> (pcase-let ((`(let ,bs (*when *,c . ,r)) '(let ((foo 42)) (*zot *1 2
3))))
         (list 'bs bs 'c c 'r r))
(bs
 ((foo 42))
 c 1 r
 (2 3))

ELISP> (pcase '(let ((foo 42)) (*when *1 2 3))
         (`(let ,bs (*zot *,c . ,r)) (list 'bs bs 'c c 'r r)))
nil

pcase correctly fails to match *when *and *zot*, while pcase-let seems to
happily go ahead.

All the best

-- 
Marco Antoniotti
Somewhere over the Rainbow

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Marco Antoniotti <marcoxa <at> gmail.com>
Cc: brubar.cs <at> gmail.com, monnier <at> iro.umontreal.ca, 70597-done <at> debbugs.gnu.org
Subject: Re: bug#70597: Problem in pcase-let?
Date: Sat, 04 May 2024 14:35:43 +0300

> From: Marco Antoniotti <marcoxa <at> gmail.com>
> Date: Thu, 2 May 2024 13:06:58 +0200
> Cc: Stefan Monnier <monnier <at> iro.umontreal.ca>, brubar.cs <at> gmail.com, 70597 <at> debbugs.gnu.org
> 
> it's your call.  But please change the doc string to clarify that pcase-let does not do "symbol equality" pattern
> matching, but only structural matching.  Adding an example like the following will help.
> 
> (pcase-let ((`(foo ,x 23 ,y) '(bar 11 baz 22))) (list x y))

This is already explained in the ELisp manual, and the doc string
already says

  Each EXP should match its respective PATTERN (i.e. be of structure
  compatible to PATTERN)

So I don't think we need to do anything else here, and I'm closing
this bug.

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