On Thu, Nov 23, 2006 at 10:20:51AM +0000, Chris Kuklewicz wrote:
Some of the other regex-* libraries are interfaces to c-library backends (pcre and tre) and it is not GHC's place to come with copies of those libraries. But GHC used regex internally, so it must come with at least a single backend.
A problem with these packages is that they're a good deal less portable than the Text.Regex they replaced. They use multi-parameter type classes, but they also rely on late overlapping resolution, which is a GHC-only feature. That is, instances overlap, but they're only used outside of the overlap, e.g.: instance (RegexLike a b) => RegexContext a b (Array Int b) instance (RegexLike a b) => RegexContext a b MatchArray type MatchArray = Array Int (MatchOffset, MatchLength) type MatchOffset = Int type MatchLength = Int These overlap at RegexContext a (Int,Int) (Array Int (Int,Int)), but as long as you don't use that instance GHC doesn't complain. (And you won't, because there's no instance RegexLike a (Int,Int), but overlaps are decided by comparing instance heads only.) Similarly instance (RegexLike a b) => RegexContext a b [Array Int b] instance (RegexLike a b) => RegexContext a b [MatchArray] and also instance (RegexLike a b) => RegexContext a b [b] instance (RegexLike a b) => RegexContext a b [MatchArray] instance (RegexLike a b) => RegexContext a b [(MatchOffset,MatchLength)] Can anything be done about that?