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Re: regexp and valid-sre?

On Tue, Nov 26, 2013 at 10:00:10AM -0800, Michael Montague wrote:
> I don't think that these are strong arguments for having 'valid-sre?'. 
> An implementation for which compiling is expensive, could easily 
> internally do the "is it valid"-type check before compiling. Having it 
> in the interface adds no functionality that is not already easily available.

You're missing the part where I said "on-the-fly".  If it _is_ valid,
this will be unacceptably slow if you're only interested in providing
feedback to the user whether their currently entered expression is
valid or not.  I don't think this feature is far-fetched: programs
like RegexBuddy do this, and an enhanced Scheme IDE could also do
something like that.

The valid-sre? test is more primitive, and it doesn't make sense to
wrap this up in the constructor, requiring people to create a complete
regex object (with the overhead and memory garbage it creates) just
to get at this information is a bad idea.