On 11/26/2013 10:19 AM, Peter Bex wrote:
> 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.

On today's computers, how complex would the regular expression have to
be for it to be unacceptably slow? For it to be slow enough for a person
to notice in interactive use?

I have implemented a NFA regular expression package, but never a DFA one.