GNU bug report logs - #2816
regexp-opt: does not optimize 'Abc' and 'abc'

Previous Next

To reply to this bug, email your comments to 2816 AT debbugs.gnu.org.
There is no need to reopen the bug first.

Toggle the display of automated, internal messages from the tracker.

Message #5 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Jari Aalto <jari.aalto <at> cante.net>
To: Emacs bug BTS <submit <at> debbugs.gnu.org>
Subject: regexp-opt: does not optimize 'Abc' and 'abc'
Date: Sun, 29 Mar 2009 18:28:55 +0300

A)

    (regexp-opt
      '("Abc"
        "abc"))

    => "\\(?:[Aa]bc\\)"

B)

    (regexp-opt
      '("Abc"
        "def"
        "abc"))

    => "\\(?:Abc\\|abc\\|def\\)"

Shouldn't regexp-opt optimize B case as well?

Jari

Message #12 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Jari Aalto <jari.aalto <at> cante.net>
Cc: 2816 <at> debbugs.gnu.org,
        Emacs bug BTS <submit <at> debbugs.gnu.org>
Subject: Re: bug#2816: regexp-opt: does not optimize 'Abc' and 'abc'
Date: Sun, 29 Mar 2009 13:13:09 -0400

> A)

>     (regexp-opt
>       '("Abc"
>         "abc"))

>     => "\\(?:[Aa]bc\\)"

> B)

>     (regexp-opt
>       '("Abc"
>         "def"
>         "abc"))

>     => "\\(?:Abc\\|abc\\|def\\)"

> Shouldn't regexp-opt optimize B case as well?

The `opt' of regexp-opt should be understood in the sense of
optimization used in compilers, not in the formal mathematical sense of
"optimal".  I.e. it does some effort to improve things, but without any
guarantee about what is and what isn't optimized.

So, yes, it would be good if it did do what you suggest, but it's not
a bug if it doesn't.


        Stefan

Message #26 received at 2816-close <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 2816-close <at> debbugs.gnu.org, Jari Aalto <jari.aalto <at> cante.net>
Subject: Re: bug#2816: regexp-opt: does not optimize 'Abc' and 'abc'
Date: Tue, 11 Mar 2025 09:44:31 -0700

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

>> A)
>
>>     (regexp-opt
>>       '("Abc"
>>         "abc"))
>
>>     => "\\(?:[Aa]bc\\)"
>
>> B)
>
>>     (regexp-opt
>>       '("Abc"
>>         "def"
>>         "abc"))
>
>>     => "\\(?:Abc\\|abc\\|def\\)"
>
>> Shouldn't regexp-opt optimize B case as well?
>
> The `opt' of regexp-opt should be understood in the sense of
> optimization used in compilers, not in the formal mathematical sense of
> "optimal".  I.e. it does some effort to improve things, but without any
> guarantee about what is and what isn't optimized.
>
> So, yes, it would be good if it did do what you suggest, but it's not
> a bug if it doesn't.

Without a proposed patch, I think it's unlikely that we'll make much
progress here.  After 16 years, I'm closing this bug now.

If anyone wants to propose improvements to `regexp-opt`, please open a
new bug report.

Message #29 received at 2816-close <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 2816-close <at> debbugs.gnu.org, Jari Aalto <jari.aalto <at> cante.net>
Subject: Re: bug#2816: regexp-opt: does not optimize 'Abc' and 'abc'.
Date: Tue, 11 Mar 2025 09:46:10 -0700

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

>> A)
>
>>     (regexp-opt
>>       '("Abc"
>>         "abc"))
>
>>     => "\\(?:[Aa]bc\\)"
>
>> B)
>
>>     (regexp-opt
>>       '("Abc"
>>         "def"
>>         "abc"))
>
>>     => "\\(?:Abc\\|abc\\|def\\)"
>
>> Shouldn't regexp-opt optimize B case as well?
>
> The `opt' of regexp-opt should be understood in the sense of
> optimization used in compilers, not in the formal mathematical sense of
> "optimal".  I.e. it does some effort to improve things, but without any
> guarantee about what is and what isn't optimized.
>
> So, yes, it would be good if it did do what you suggest, but it's not
> a bug if it doesn't.

Without a proposed patch, I think it's unlikely that we'll make much
progress here.  After 16 years, I'm closing this bug now.

If anyone wants to propose improvements to `regexp-opt`, please open a
new bug report.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.