Re: Ann: regex pack

On Mon, Sep 16, 2013 at 1:21 AM, Richard A. O'Keefe <[email protected]>wrote:

>
> On 14/09/2013, at 7:49 AM, Michael Hendricks wrote:
>
> > I love DCGs as much as the next Prolog fan, but sometimes a tiny regular
> > expression will do the job.  Or perhaps regular expressions are part of
> > your app's UI.  Anyway, this
> > pack<http://www.swi-prolog.org/pack/list?p=regex>supports many
> > features of Perl compatible regex (see link for full support).
>
> Oh dear.  The huge merit of regular expressions is that they take
> linear time.  The huge defect of Perl irregular expressions is
> that they can take exponential time.
>

Yeah, they can get pretty nasty.  Mark Jason Dominus shows that solving
Perl regular expressions is NP-Hard: http://perl.plover.com/NPC/


> Apart from that, if you can plug re2 in, why would you want
> anything else?
>

Some environments can't call external C libraries so a pure Prolog
implementation is all that's available.


> Didn't Peter Schachte write a regular expression library for Prolog?
>

After several searches, I've been unable to find it.  I'll gladly adopt an
existing, stable implementation if one's available.

-- 
Michael
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