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

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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

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