RE: check the type of the $pattern argument to a regul

> I agree with the people who think a pattern to test patterns 
> is an insoluble problem.
> 
> There are an infinite number of valid regular expressions, 
> and an even larger number of invalid ones. Plus all those 
> inbetween regular expressions which are valid, but not what you meant.

I think you're having slight problems with your infinities there: both are
countable infinities and are therefore equal in magnitude.

And there's an infinite number of integers, but that doesn't stop you
writing a pattern that matches them all.

So while the problem might be insoluble, it has nothing to do with the size
of the set you are trying to match.

Michael Kay
http://www.saxonica.com/