From: Eric Luo <eric.wenbl@...>
Date: 2005-07-03T23:37:50+09:00
Subject: Re: Ask for help about Regexp

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Yes, It's really what I want.=20
Seem to be a little diffcult to resolve the problem properly.
I had to work around my biz requirement 'cause I cound't manage
to do with it

Thank you for your help

On 7/1/05, Daniel Brockman <daniel@brockman.se> wrote:
>=20
> Nikolai Weibull <mailing-lists.ruby-talk@rawuncut.elitemail.org> writes:
>=20
> > Eric Luo wrote:
> >
> >> I need to match my input dynamically by Regexp, For example: I want
> >> match to this regexp: mask =3D /\d{10}tt\d{0, 5} then I give my input
> >> byte by byte. And I want to be noticed at the first time when it is
> >> impossible for me to match my input to the regexp mask. so if i input
> >> 34789d, when I the input the character 'd', I will be noticed.
> >>
> >> I wonder if it's possible or not. if it is, how could I do that?
> >
> > Well, you can't easily do that. You could write a regex that matches
> > valid prefixes of the strings of the language of the final regex, but
> > that can become quite complicated. You should probably rethink your
> > algorithm,
>=20
> Nikolai is right: you can't easily do that. But I think it would be
> easy to modify the regular expression engine to make it possible.
> Unless I am mistaken, the only information you need is whether or not
> the engine ever wanted to look past the end of the input string.
>=20
> If the engine ever managed to consume all characters and still be
> hungry for more, then your string is a valid prefix. Conversely, if
> the engine did not do this, then your string is not a valid prefix.
> Note that merely consuming all characters is not sufficient; the match
> has to fail due to lack of additional input.
>=20
> I just posted about this on Perl Monks,
>=20
> <http://perlmonks.org/index.pl?node_id=3D471541>
>=20
> so consider following up there if you have anything to add.
>=20
> I don't feel like hacking this into regex.c right now, and I'm not
> sure what the API should be like.
>=20
> But I do think it would be a useful feature. The fact that noone
> seems to have wanted it before baffles me. Perhaps up until now,
> noone even considered the possibility.
>=20
> --
> Daniel Brockman <daniel@brockman.se>
>=20
>=20
>

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