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Re: 21.1 incorrect Regular expression parsing


From: Stefan Monnier
Subject: Re: 21.1 incorrect Regular expression parsing
Date: 11 Dec 2001 17:51:36 -0500
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.1.50

>>>>> "Jari" == Jari Aalto+mail emacs <address@hidden> writes:
> expressions to be written: double-triple-quadruple... quantifiers are
> incorrect and should signal parser error.

To me they're not incorrect because a++ is parsed like ((a)+)+ so it
should behave just like a+ (and I believe that it does under Emacs-20
and Emacs-21).

> It's different if the behavior is defined: e.g. in Perl some
> double-quantifiers like *? have a special meaning which were
> used to extend the regular expression grammar.

In Emacs-21, a+? has the same meaning as for Perl.

> I Still consider it bad practice to leave door open to a
> construct "++" in Emacs. Please consider putting a plug to it.

As I said, it's a backward compatibility risk, so it will only
be done if there's a particular problem to be solved (not necessarily
an enormous one, mind you, but more than just taste).


        Stefan



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