Front page | perl.perl6.language.regex |
Postings from December 2000
>>>>> "DTC" == Deven T Corzine <deven@ties.org> writes: DTC> The pattern in question is "b.*?d". Obviously, this matches "b", DTC> followed by something else, followed by "d". What "something DTC> else" should be is the issue at hand. That portion of the regexp DTC> is just ".*?" -- the "." matches any character (except newlines, DTC> depending on the mode), the "*" modifies the "." to match "zero DTC> or more" of "any character", and the "?" modifies the ".*" to DTC> match "zero or more" of "any character", but "matching the DTC> minimum number of times possible". Hence, the ".*?" can be DTC> summarized as "match anything, but keep the match as short as DTC> possible". DTC> TAKEN IN ISOLATION, the most natural interpretation for the DTC> programmer to make, at this high semantic level, is that it will DTC> match "bccccd" rather than "bbbbccccd", because the ".*?" is DTC> expected to match as little as possible (though as much as DTC> necessary), and "cccc" is as little as it can possibly match DTC> while allowing the entire regexp to match. "bbbbccccd" is a DTC> longer match, and counterintuitive compared to the semantic DTC> description of what "b.*?d" should match. just add the semantic part of leftmost or first and you have your answer. it is defined that way in the current semantics as well as in the implementation. regardless, having the semantics of your way would entail finding ALL possible matches and then scanning them for the shortest one. there is no other way to define that behavior than that. how could you find the true shortest match without finding all of the matches first? the leftmost/first semantic eliminates that problem. so please add those words and then restate your argument. you can't. the result you want does not jibe with first or leftmost. it is a different semantic. and the current one is used for many reasons including history, simplicity of semantics and even (drat!) implementation and speed. as for perl6 doing what you want, write a regex engine and plug it in. but the default perl6 regexes should behave the same as perl5's for all the right reasons including backwards compatibility. uri -- Uri Guttman --------- uri@sysarch.com ---------- http://www.sysarch.com SYStems ARCHitecture, Software Engineering, Perl, Internet, UNIX Consulting The Perl Books Page ----------- http://www.sysarch.com/cgi-bin/perl_books The Best Search Engine on the Net ---------- http://www.northernlight.com