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

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Package: emacs; Severity: wishlist; Reported by: Jari Aalto <jari.aalto@HIDDEN>; dated Sun, 29 Mar 2009 15:35:04 UTC; Maintainer for emacs is bug-gnu-emacs@HIDDEN.
Tags removed: patch Request was from Glenn Morris <rgm@HIDDEN> to control@HIDDEN. Full text available.
Severity set to `wishlist' from `normal' Request was from Jari Aalto <jari.aalto@HIDDEN> to control@HIDDEN. Full text available.

Message received at 2816@HIDDEN:


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From: Stefan Monnier <monnier@HIDDEN>
To: Jari Aalto <jari.aalto@HIDDEN>
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'
Message-ID: <jwvy6uo9rwy.fsf-monnier+emacsbugreports@HIDDEN>
References: <877i28nya0.fsf@HIDDEN>
Date: Sun, 29 Mar 2009 13:13:09 -0400
In-Reply-To: <877i28nya0.fsf@HIDDEN> (Jari Aalto's message of "Sun,
	29 Mar 2009 18:28:55 +0300")
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> 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
Acknowledgement sent to Stefan Monnier <monnier@HIDDEN>:
Extra info received and forwarded to list. Copy sent to Emacs Bugs <bug-gnu-emacs@HIDDEN>. Full text available.
Information forwarded to bug-submit-list@HIDDEN, Emacs Bugs <bug-gnu-emacs@HIDDEN>:
bug#2816; Package emacs. Full text available.

Message received at submit@HIDDEN:


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From: Stefan Monnier <monnier@HIDDEN>
To: Jari Aalto <jari.aalto@HIDDEN>
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'
Message-ID: <jwvy6uo9rwy.fsf-monnier+emacsbugreports@HIDDEN>
References: <877i28nya0.fsf@HIDDEN>
Date: Sun, 29 Mar 2009 13:13:09 -0400
In-Reply-To: <877i28nya0.fsf@HIDDEN> (Jari Aalto's message of "Sun,
	29 Mar 2009 18:28:55 +0300")
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> 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
Acknowledgement sent to Stefan Monnier <monnier@HIDDEN>:
Extra info received and forwarded to list. Copy sent to Emacs Bugs <bug-gnu-emacs@HIDDEN>. Full text available.
Information forwarded to bug-submit-list@HIDDEN, Emacs Bugs <bug-gnu-emacs@HIDDEN>:
bug#2816; Package emacs. Full text available.
Tags added: patch Request was from Jari Aalto <jari.aalto@HIDDEN> to control@HIDDEN. Full text available.

Message received at submit@HIDDEN:


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From: Jari Aalto <jari.aalto@HIDDEN>
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
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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
Acknowledgement sent to Jari Aalto <jari.aalto@HIDDEN>:
New bug report received and forwarded. Copy sent to Emacs Bugs <bug-gnu-emacs@HIDDEN>. Full text available.
Report forwarded to bug-submit-list@HIDDEN, Emacs Bugs <bug-gnu-emacs@HIDDEN>:
bug#2816; Package emacs. Full text available.
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