GNU bug report logs - #68509
30.0.50; pcase-dolist matches backquote pattern incorrectly

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Message #29 received at 68509 <at> debbugs.gnu.org (full text, mbox):

From: Ihor Radchenko <yantar92 <at> posteo.net>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: Jim Porter <jporterbugs <at> gmail.com>, 68509 <at> debbugs.gnu.org
Subject: Re: bug#68509: 30.0.50; pcase-dolist matches backquote pattern
 incorrectly
Date: Mon, 19 Feb 2024 18:16:37 +0000

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

> The difficulty in resolving this can be illustrated with the following
> pattern:
>
>     `(a . ,b)
>
> This pattern leads to two tests: (consp VAL) and (eq 'a (car VAL)).
> When destructuring, we want to throw away both tests (we want to throw
> away most tests, except those needed to choose between two `or`
> branches).
>
> We could decide to emit a warning because we silently skip
> the `eq` test, which would help the coders understand that the pattern
> doesn't do what they think.
> But emitting that same warning because we silently skip the `consp` test
> would be really annoying because rewriting the pattern to avoid this
> is impractical.

May you please elaborate how this example is related to destructuring
from user perspective? It appears to me that you are talking about
implementation details of `pcase', which are elusive to me.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>

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