Compare regular expressions

[Diez B. Roggisch]

Thomas Dybdahl Ahle schrieb:
> Hi, I'm writing a program with a large data stream to which modules can 
> connect using regular expressions.
> 
> Now I'd like to not have to test all expressions every time I get a line, 
> as most of the time, one of them having a match means none of the others 
> can have so.
> 
> But ofcource there are also cases where a regular expression can 
> "contain" another expression, like in:
> "^strange line (\w+) and (\w+)$" and "^strange line (\w+) (?:.*?)$" in 
> which case I'd like to first test the seccond and only if it mathces test 
> the seccond.
> 
> Do anybody know if such a test is possible?
> if exp0.contains(exp1): ...

It's not. For the simplest of expressions one might come up with a 
relation between them, but even that would be hard. General case? No chance.

Diez