[thelist] Regular expression to check if other regularexpressions are valid
Carl Edwards
edwards at vitesse.com
Wed Jun 22 16:49:20 CDT 2005
Hello,
If eval is available in your language of choice you can
use it to test the validity of a regex.
/Carl
> -----Original Message-----
> From: lustig at brandeis.edu [mailto:lustig at brandeis.edu]
> Sent: Wednesday, June 22, 2005 1:25 PM
> To: VOLKAN ÖZÇELÝK; thelist at lists.evolt.org
> Subject: Re: [thelist] Regular expression to check if other
> regularexpressions are valid
>
>
> > which is a valid regular expression with infinitely many positive
> > lookaheads. I've forgotten the stuff with theory of large
> numbers etc,
> > but hope that an interested can prove that it is
> impossible to match
> > such a regex with a regex.
>
> I definitely think that it is possible to create a regex to
> match other
> regexes... I was going to try doing it myself but was
> wondering if someone
> has done it already. THe reason why I think that it is
> possible, is because
> there *is* a pattern to regular expressions. The PHP parser,
> for example,
> knows when there is a syntax error in a regular expression,
> because it stops
> parsing it and throws an error. There is no way to check a
> regular expression
> to see if it does what you want it to do (besides doing a
> rigorous proof) but
> there probably is a (ridiculously complex) regular
> expression which will
> decide whether another regular expression is a valid regex.
>
> My idea on this is that the regular expression would look
> something like this,
> but more fleshed out:
>
> (something to check beginning of regex) (something to check
> inside of regex)
> (something to check end and modifiers)
>
> the "something to check inside of regex" would look like this:
>
> [(list of possible characters like \s\S\\s\\S\.\\. etc.)]*
>
> and then just put that in a bunch of possible ways to
> organize a regex that
> allows for nesting it in parentheses, etc.
>
> Jason
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