GNU bug report logs - #37659
rx additions: anychar, unmatchable, unordered-or

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: bug-gnu-emacs <at> gnu.org
Subject: rx additions: anychar, unmatchable, unordered-or
Date: Tue, 8 Oct 2019 11:36:44 +0200

[Message part 1 (text/plain, inline)]

Three minor rx additions follow:

* Add `anychar' as an alias for `anything': the latter suggests an expression that can match any string, while in reality it only matches a single character. The documentation now uses `anychar' as the preferred name. (`any-char' would also be possible, but is longer.)

* Add `unmatchable' for a never-match regexp. This follows the previously introduced variable `regexp-unmatchable'.

* Add `unordered-or' as a variant of `or' without the left-to-right match order guarantee. It allows unconditional regexp-opt optimisations, and is particularly useful for matching sets of keywords. With rx-let and rx-define, it also has the potential for better compositionality, allowing expressions to be put together from smaller parts.

Abstractly: while `or' is associative, `unordered-or' is also commutative.

The name `unordered-or' is descriptive but phonetically (and lexically) somewhat weak. Strong alternatives welcome.

[0001-Add-anychar-as-alias-to-anything-in-rx.patch (application/octet-stream, attachment)]

[0002-Add-unmatchable-as-alias-for-or-in-rx.patch (application/octet-stream, attachment)]

[0003-Add-rx-unordered-or-construct.patch (application/octet-stream, attachment)]

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