GNU bug report logs - #76731
C-style comment regexp example in (info "(elisp)Rx Notation") is not correct

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Package: emacs;

Reported by: "Yue Yi" <include_yy <at> qq.com>

Date: Tue, 4 Mar 2025 04:09:02 UTC

Severity: wishlist

Done: Mattias Engdegård <mattias.engdegard <at> gmail.com>

Bug is archived. No further changes may be made.

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Message #27 received at 76731 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattias.engdegard <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: Yue Yi <include_yy <at> qq.com>, 76731 <at> debbugs.gnu.org,
 Stefan Kangas <stefankangas <at> gmail.com>
Subject: Re: bug#76731: C-style comment regexp example in (info "(elisp)Rx
 Notation") is not correct
Date: Tue, 20 May 2025 13:48:45 +0200

20 maj 2025 kl. 00.42 skrev Stefan Monnier <monnier <at> iro.umontreal.ca>:

> Our regexp engine lacks to "switch" kind of operation needed for that.
> After a series of `*` we have two mutually exclusive paths, depending on whether
> the next char is a `/` or something else, but we don't have a "look
> ahead" so we have to push a backtrack-point before we try to match the
> next char with `/`.

All true but we do have the ad-hoc non-backtracking optimisation. Right now it's only used for 'simple' patterns as in

(: (* "a") "b")

but there shouldn't be any reason not to use it for, say,

(: (* "a" ARBITRARY-PATTERN) "b")

should it? Except for ease of implementation, of course.
This bug report was last modified today.

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