Re: Future of our regular expression code

On Sun, Feb 19, 2012 at 1:55 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Dimitri Fontaine <dimitri(at)2ndQuadrant(dot)fr> writes:
>> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>>> Yeah ... if you *don't* know the difference between a DFA and an NFA,
>>> you're likely to find yourself in over your head.  Having said that,
>
>> So, here's a paper I found very nice to get started into this subject:
>>   http://swtch.com/~rsc/regexp/regexp1.html
>
> Yeah, I just found that this afternoon myself; it's a great intro.
>
> If you follow the whole sequence of papers (there are 4) you'll find out
> that this guy built a new regexp engine for Google, and these papers are
> basically introducing/defending its design.  It turns out they've
> released it under a BSD-ish license, so for about half a minute I was
> thinking there might be a new contender for something we could adopt.
> But there turn out to be at least two killer reasons why we won't:
> * it's in C++ not C
> * it doesn't support backrefs, as well as a few other features that
>  maybe aren't as interesting but still would represent compatibility
>  gotchas if they went away.

Another interesting library, technology-wise, is libtre:

http://laurikari.net/tre/about/
http://laurikari.net/tre/documentation/

NetBSD plans to replace the libc regex with it:

http://netbsd-soc.sourceforge.net/projects/widechar-regex/
http://groups.google.com/group/muc.lists.netbsd.current-users/browse_thread/thread/db5628e2e8f810e5/a99c368a6d22b6f8?lnk=gst&q=libtre#a99c368a6d22b6f8

Another useful project - AT&T regex tests:

http://www2.research.att.com/~gsf/testregex/

About our Spencer code - if we don't have resources (not called Tom)
to clean it up and make available as library (in short term - at least
to TCL folks) we should drop it. Because it means it's dead end,
however good it is.

--
marko