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From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Ihor Radchenko <yantar92@posteo.net>
Cc: Eli Zaretskii <eliz@gnu.org>,
	 mattiase@acm.org,  arstoffel@gmail.com, eller.helmut@gmail.com,
	 dmcc2@hypnicjerk.ai,  pipcet@protonmail.com,
	emacs-devel@gnu.org,  acorallo@gnu.org,  stefankangas@gmail.com
Subject: Re: [PATCH] add compiled regexp primitive lisp object
Date: Tue, 24 Dec 2024 00:37:15 -0500	[thread overview]
Message-ID: <jwvseqdhd2g.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <87y106jr4i.fsf@localhost> (Ihor Radchenko's message of "Mon, 23 Dec 2024 16:33:49 +0000")

> Having compiler regexp object exposed to Elisp would open the
> following extra opportunities:

Nitpick: there are various ways to "Add compiled regexp primitive lisp
object", and not all of them would really expose those objects in ways
would allow the following points.

> 1. They could be inspected from Elisp, and hopefully optimized
>    better. For now, there is simply no way to detect which parts of
>    regexps are slow and which are not.

You can now/already use `re--describe-compiled` to inspect the compiled
regexps used by Emacs's regexp engine.

> 2. They could maybe even be constructed from Elisp, opening
>    opportunities for custom regexp compilers that can be tailored to
>    specific application needs rather than having to stick to hard-coded
>    generic tradeoffs Emacs has to do without knowing the purpose of a
>    regexp.

Definitely.  And since it would be one in ELisp, there could be dozens
of specialized compilers in ELPA packages to choose from.  🙂

Eli wrote:
> If we can optimize them from Lisp, we should be able to do the same
> in C.

`re_compile_pattern` is not terribly easy to improve.  Among other
things because it needs to be fast, single pass, etc...

If regexp objects are exposed in such a way that we can build them from
ELisp and write them to `.elc` files, then anyone can write their own
regexp compiler for their own regexp flavor, which can be as slow as
they like because it won't slow down anyone else.

> If you explain what kind of optimization opportunities you had in
> mind, we could discuss how to implement that.  In any case, adding
> APIs for regexp optimizations doesn't require to have compiled regexp
> objects.

If we want to be able to compile regexps to a DFA-style compiled form,
we'll need to extend the regexp bytecode, of course, but it would either
require we implement that compilation in C (which could be a fair bit
of work) or it would require changing `re_compile_pattern` to recognize
new elements in the regexp-string corresponding to those new
bytecode instructions.

I have the impression it would be simpler to expose the bytecode vectors
to ELisp (so as to be able to build them and print+read them) and do the
rest in ELisp.  Or course, we'd still want to keep `re_compile_pattern`
to handle the cases where we can't (or can't be bothered to) pre-compile
the regexp and hence where the compilation to bytecode needs to be as
fast as possible.


        Stefan




  parent reply	other threads:[~2024-12-24  5:37 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-07-30  5:08 [PATCH] add compiled regexp primitive lisp object Danny McClanahan
2024-07-30 13:02 ` Philip Kaludercic
2024-07-31 22:33   ` dmcc2
2024-08-01  1:04 ` Pip Cet
2024-08-04 23:38   ` Danny McClanahan
2024-08-05  3:47     ` dmcc2
2024-08-05  4:39   ` Danny McClanahan
2024-08-05  7:15     ` Danny McClanahan
2024-08-05 17:55     ` Pip Cet
2024-08-06 15:15       ` Danny McClanahan
2024-08-06 15:57         ` Eli Zaretskii
2024-08-07  4:28           ` Danny McClanahan
2024-08-06 18:18         ` Pip Cet
2024-08-06 18:38           ` Eli Zaretskii
2024-08-07  4:23             ` Danny McClanahan
2024-08-07 12:00               ` Eli Zaretskii
2024-08-07 12:43                 ` Helmut Eller
2024-08-07 13:40                   ` Augusto Stoffel
2024-08-07 15:23                     ` Danny McClanahan
2024-08-14  1:32                     ` Stefan Monnier
2024-11-26 18:05                       ` Danny McClanahan
2024-11-26 18:50                         ` Danny McClanahan
2024-12-08 15:24                         ` Danny McClanahan
2024-12-09 15:12                           ` Stefan Monnier
2024-12-09 15:13                             ` Stefan Monnier
2024-12-22 19:14                       ` Ihor Radchenko
2024-12-22 19:24                         ` Eli Zaretskii
2024-12-22 20:02                           ` Ihor Radchenko
2024-12-22 20:20                             ` Eli Zaretskii
2024-12-22 20:31                               ` Ihor Radchenko
2024-12-23 13:38                                 ` Björn Bidar
     [not found]                                 ` <8634ie60jd.fsf@gnu.org>
2024-12-23 16:33                                   ` Ihor Radchenko
2024-12-23 16:49                                     ` Eli Zaretskii
2024-12-23 17:10                                       ` Ihor Radchenko
2024-12-24 21:16                                         ` Björn Bidar
2024-12-24  5:37                                     ` Stefan Monnier [this message]
2024-12-24  9:30                                       ` Ihor Radchenko
2024-12-24 15:14                                         ` Stefan Monnier
2024-08-07 15:02                 ` Danny McClanahan
2024-08-07 15:23                   ` Eli Zaretskii
2024-08-14  1:25               ` Stefan Monnier
2024-08-07  7:59           ` Danny McClanahan
2024-08-06 12:08     ` Eli Zaretskii
2024-08-01  8:30 ` Andrea Corallo
2024-08-01 10:06   ` Gerd Möllmann
2024-08-06 13:47   ` Danny McClanahan
2024-08-06 13:57     ` Danny McClanahan
2024-08-07  7:21     ` Andrea Corallo
2024-08-07  8:27       ` Danny McClanahan

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