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bug#2881: 23.0.91; inconsistent regexps with "explicitly numbered group"


From: Andreas Schwab
Subject: bug#2881: 23.0.91; inconsistent regexps with "explicitly numbered group"
Date: Fri, 03 Apr 2009 23:32:01 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.92 (gnu/linux)

Andreas Schwab <address@hidden> writes:

> Joe Corneli <address@hidden> writes:
>
>> Please execute the following forms with C-x C-e.  Form 1
>> and Form 3 return `t' (Yes, we are looking at the
>> indicated regular expression), whereas Form 2 returns
>> `nil' (even though from the Elisp reference page "34.3.1.3
>> Backslash Constructs in Regular Expressions", it appears
>> that this form ought to return `t' like the others).
>
>      `\|' applies to the largest possible surrounding expressions.
>      Only a surrounding `\( ... \)' grouping can limit the grouping
>      power of `\|'.
>
>> (let ((possible-environments
>>        "\\(?1:lisp\\)\\|\\(?1:idea\\)\\|\\(?1:common\\)") )
>>       (looking-at
>>             (concat "\n*?\\\\begin{"
>>                     possible-environments
>>                     "}")))
>
>
> The three alternatives of this regexp are "\n*?\\\\begin{\\(?1:lisp\\)",
> "\\(?1:idea\\)" and "\\(?1:common\\)".

The last one is "\\(?1:common\\)}", of course.

Andreas.

-- 
Andreas Schwab, address@hidden
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."






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