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Re: writing new regexp functions

From: Jeremy Drake <pgsql(at)jdrake(dot)com>
To: David Fetter <david(at)fetter(dot)org>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: writing new regexp functions
Date: 2007-02-02 06:16:54
Message-ID: Pine.BSO.4.64.0702012204460.28908@resin.csoft.net (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
On Thu, 1 Feb 2007, David Fetter wrote:

> On Thu, Feb 01, 2007 at 05:11:30PM -0800, Jeremy Drake wrote:
> > Anyway, the particular thing I was writing was a function like
> > substring(str FROM pattern) which instead of returning just the
> > first match group, would return an array of text containing all of
> > the match groups.

If you are subscribed to -patches, I sent my code to date there earlier
this evening.  I also said that I wanted to make a function that split on
a pattern (like perl split) and returned setof text.

> That'd be great!  People who use dynamic languages like Perl would
> feel much more at home having access to all the matches.  While you're
> at it, could you could make pre-match and post-match (optionally--I
> know it's expensive) available?

I could, but I'm not sure how someone would go about accessing such a
thing.  What I just wrote would be most like this perl:
@foo = ($str=~/pattern/);

Where would pre and post match fit into this?  Are you talking about a
different function?  Or sticking prematch at the beginning of the array
and postmatch at the end?  I could also put the whole match somewhere
also, but I did not in this version.

The code I wrote returns a text[] which is one-dimensional, has a lower
bound of 1 (as most postgres arrays do), where if there are n capture
groups, ra[1] has the first capture group and ra[n] has the last one.
Since postgres has an option to make different lower bounds, I suppose I
could have an option to put the prematch in [-1], the entire match in [0],
and the postmatch in [n+1].  This seems to be odd to me though.

I guess I'm saying, I agree that the entire match, prematch, and postmatch
would be helpful, but how would you propose to present these to the user?

>
> Cheers,
> D
>

-- 
To err is human, to forgive, beyond the scope of the Operating System.

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