Haskell platform related proposal: update regex to latest versions

[Chris Kuklewicz]

I have added this to the trac wiki at
http://trac.haskell.org/haskell-platform/wiki/Library/regex-base

Chris Kuklewicz proposes:

As the writer and maintainer of the regex-(base|posix|compat) packages I would 
like suggest the following.

The Haskell platform should upgrade from the 0.72 version of regex-base to the 
0.93.1 version.  Similar updates to the latest releases of regex-posix and 
regex-compat would also be made.  The old version has been kicking around too 
long, partly because I have not bothered to push updating the GHC bundle.

The regex-base update adds makeRegexM and makeRegexOptsM which allow for saner 
error handling when compiling regular expressions, they use "fail" instead of 
"error".  It would be possible to switch to !MonadError or perhaps the new 
exceptions, discussion of this is welcome.

The older version of regex-base has lazy overlapping instances of !RegexContex 
which GHC allows and Hugs forbids, so the new version of regex-base has newtypes 
that force the user to be more explicit:
{{{
newtype AllSubmatches f b = AllSubmatches {getAllSubmatches :: (f b)}
newtype AllTextSubmatches f b = AllTextSubmatches {getAllTextSubmatches :: (f b)}
newtype AllMatches f b = AllMatches {getAllMatches :: (f b)}
newtype AllTextMatches f b = AllTextMatches {getAllTextMatches :: (f b) }
}}}
It would be possible to include most (or perhaps all) of the old instances, 
either as a sub-module or conditionally compiled, again discussion of this is 
welcome.