On Tue, 2006-03-28 at 14:32 +0100, Simon Peyton-Jones wrote:
My current take, FWIW.
* MPTCs are very useful. They came along very rapidly (well before H98). I think we must put them in H'
* But MPTCs are hamstrung without FDs or ATs
* FDs and ATs are of the same order of technical difficulty, as Martin says
* ATs are (I believe) a bit weaker from the expressiveness point of view (zip example), but are (I believe) nicer to program with.
* BUT we have way more experience with actually programming with FDs. ATs fail the "well-established" test by a mile.
* Largely due to Martin's work, we now have a much better handle on just what restrictions on FDs make type inference tractable. So I believe there is a solid MPTC+FD story that we could embody in H'.
* Medium term, I think ATs may *at the programming-language level* displace FDs, because they are nicer to program with. But that's just my opinion, and we don't have enough experience to know one way or the other.
This analysis is similar to what I have here: http://hackage.haskell.org/trac/haskell-prime/wiki/MultiParamTypeClassesDile... Could someone flesh out the wiki w/ Simon's data and links to the new information from Martin? peace, isaac