Ann: regex pack

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).

As the semantic version number indicates, the API is very early and will
probably change. It currently uses =~ (as do Haskell and Perl), but that
gives no access to captured values.  A YAP-compatible API would support
captures so I might do that.  I'd also love to use
prolog_load_context(variable_names, _) with regex named captures to
automatically bind clause variables by name.

I considered supporting quasiquotation (so one doesn't have to escape all
the slashes), but decided for now that a regex that complex should probably
be rewritten as a DCG anyway.

The regular expression engine is currently a naive interpreter.  I partly
did that so that I have an interpreter to play with as I experiment with
some partial evaluation ideas.  It would be cool to partially evaluate the
regex interpreter against a regex to generate fast, concise Prolog code.

Last thought: I tried to design the library to support pluggable regex
engines.  The idea is that one just adds a single line:

    :- use_module(library(regex/engine/re2)).

and your regular expressions are now handled by the re2
engine<https://code.google.com/p/re2/> (or
PCRE or POSIX or ...).  Any interest in such things?  I've used similar
tools to good effect in both Haskell and Perl.

-- 
Michael
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