From: Joe Peck <joe@...>
Date: 2006-12-22T01:48:03+09:00
Subject: Re: Regexp Question: Checking for pairs

> Regular expressions can be used to test whether a string belongs to a
> certain regular language, which is a subset of all possible languages
> (where a language is a set of strings). Regular expressions are
> equivalent to finite state automata in this respect. Since a finite
> state automata can only be in a finite number of states. You'd like to
> match a possibly infinitely large number of [joe][/joe] pairs. The FSA
> would need a new state for every extra [joe] it reads to remember it
> still needs to consume a matching [/joe] for it.
> 
> If this sounds like Chinese, just remember regexpes aren't keen on
> matching this sort of stuff. Stacks on the other hand seem to be custom
> designed for these purposes.
> 
> A.
It doesn't sound like Chinese :)

If wouldn't have to be an infinite amount of states.  Let's say these 
are the states:

State 1 - no [joe] yet.  If finds [joe], goes to state 2.  If finds 
[/joe], fails.
State 2 - [joe] found but not matching [/joe].  If it finds [joe] again 
in this state, then fails.  If it finds [/joe], increments count by 1 
and moves to state 1.

If count goes above 3, fails.

But maybe I'll use something besides a regexp, although I thought there 
would be a pretty easy way to do it.


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