bug-gnu-emacs
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

bug#34641: rx: (or ...) order unpredictable


From: Noam Postavsky
Subject: bug#34641: rx: (or ...) order unpredictable
Date: Sun, 24 Feb 2019 21:37:56 -0500

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.





reply via email to

[Prev in Thread] Current Thread [Next in Thread]