http://www.perlmonks.org?node_id=255192


in reply to Re: Re: A Perl aptitude test
in thread A Perl aptitude test

I contend that (?{ }) is not a regular expression, but a hook (a place for a Perl expression) to be evaluated by the regex engine during its matching work.

The phrase "Regular Expression" is a mathematical concept predating perl and emacs and sed. Quoting from Freidl's Mastering Regular Expressions:

Regular expressions are expressions that regulate a sequence as belonging to a set, or not belonging to a set. (What, you thought 'regular' as in 'everyday' or 'fixed interval'?)

Since (?{}) doesn't fail and cause the engine to backtrack or bail, it's not regulating anything. The regex syntax handles the wrapping stuff but the contents are what's doing the string-modifying, and the results have no direct bearing on the regulation. That's what I mean when I say that (?{}) is not a regular expression.

(I know, I'm forever editing and extending my comments with afterthoughts rather than creating new followups.)
--
[ e d @ h a l l e y . c c ]

Replies are listed 'Best First'.
Re^4: A Perl aptitude test ("regular" expressions)
by Aristotle (Chancellor) on May 03, 2003 at 01:09 UTC
    Well, even the regulating pieces of Perl's "regular expressions" are far from regular in any sense of the precise definition. The name just (incorrectly) stuck. (Recent Camels talk of "pattern matching"; I prefer that term too.) Finally, you also forget (??{ code }), which can both alter the string as well as regulate the match in procession.

    Makeshifts last the longest.