I've been wondering about something in perls regexes. If we have a sub pattern in a regex like: (LIST|OF|LISTS) can anybody think of a circumstance where "LISTS" will ever match? I've been pondering this for a while, and I cant think of any reason why one cannot consider the former to be functionally equivelent to (LIST|OF). Any ideas?

BTW, I am aware that (LISTS|OF|LIST) will produce very different results from (LIST|OF|LISTS), the point is to determine whether its fair to say that the latter contains a sub pattern that will NEVER match so that possibly a warning could be generated, or possibly the regex engine could assume its an error and silently assume it should be treated as though it were spelled (LISTS|OF|LIST).

A last point of interest, the two constructs (LISTS|OF|LIST) and (LIST|OF|LISTS) would be equivelent in many regex implementations. Perls particular implementation however does not see them as the same at all.

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demerphq

In reply to Superfluous subpatterns in regex alternations. by demerphq

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