On Wed, 30 Jun 2010, John P. Baker wrote: > I am new to PCRE, and I am looking at incorporating regular expressions into > a new product. > > I need to know whether either of the following capabilities are available, > either in PCRE, or in an add-on package - > > . Given two (2) regular expressions, does one regular expression > superset all possible pattern matches of the other regular expression?
I suspect that is very hard to determine. On my list of way-out possible things to do when I get bored (i.e. it isn't likely to happen soon) is to try to write code to generate matching strings from a compiled pattern. If this could be done, then one could compare the sets of strings, I suppose. > . Given two (2) regular expressions, does there exist any union of > potential pattern matches? Do you mean anything more complicated than A|B (where A and B are two regular expressions)? [In PCRE - and Perl - there are features that allow you to compose two patterns like that and still allow backreferences within them to work correctly, i.e. features to fiddle with the capturing parenthesis numbers.] Philip -- Philip Hazel -- ## List details at http://lists.exim.org/mailman/listinfo/pcre-dev
