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From: Noam Postavsky <npostavs@gmail.com>
To: "Mattias Engdegård" <mattiase@acm.org>
Cc: 34641@debbugs.gnu.org
Subject: bug#34641: rx: (or ...) order unpredictable
Date: Sun, 24 Feb 2019 21:37:56 -0500	[thread overview]
Message-ID: <CAM-tV-_QeFKPhJ06jWrPwj_uYEmcC3vTh0YQiS3TdUUmrX0AaQ@mail.gmail.com> (raw)
In-Reply-To: <836B8DC2-9358-40AC-83AF-7C4D960D9A53@acm.org>

On Sun, 24 Feb 2019 at 13:41, Mattias Engdegård <mattiase@acm.org> wrote:
>
> The rx (or ...) construct sometimes reorders its subexpressions, which makes its semantics unpredictable. For example,
>
> (rx (or "ab" "a") (or "a" "ab"))
> =>
> "\\(?:ab?\\)\\(?:ab?\\)"
>
> The user reasonably expects (or e1 e2) to translate to E1\|E2, where ei translates to Ei, or a semantic equivalent.

I don't see the problem, isn't "ab?" semantically equivalent to
"ab\\|a" (and "a\\|ab")?

> (Speaking of regexp-opt, it has another bug that does not affect rx: it returns the empty string if given an empty list of strings. The correct return value is a regexp that never matches anything.

This sounds familiar, though I can't locate a report for it.





  parent reply	other threads:[~2019-02-25  2:37 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-24 18:40 bug#34641: rx: (or ...) order unpredictable Mattias Engdegård
2019-02-24 19:06 ` Eli Zaretskii
2019-02-24 21:18   ` Mattias Engdegård
2019-02-24 22:44     ` Basil L. Contovounesios
2019-02-25 14:26       ` Mattias Engdegård
2019-03-02 12:33     ` Eli Zaretskii
2019-03-02 14:05       ` Mattias Engdegård
2019-03-02 14:08         ` Mattias Engdegård
2019-03-02 14:23           ` Eli Zaretskii
2019-03-02 14:37             ` Mattias Engdegård
2019-03-02 23:48       ` Phil Sainty
2019-03-03  8:54         ` Mattias Engdegård
2019-03-07  9:00           ` Phil Sainty
2019-02-25  2:37 ` Noam Postavsky [this message]
2019-02-25  9:56   ` Mattias Engdegård
2019-02-25 14:43     ` Noam Postavsky
2019-02-25 14:48       ` Mattias Engdegård

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