On Fri, May 21, 2004 at 11:04:53AM +0100, Simon Peyton-Jones wrote:

Nothing difficult in principle, but the constraint solver is one of the more delicate parts of GHC because GHC's constraint language has become so complex.

Well, as my day job is working for a constraints lab, I feel it's my bounded duty to say, "all the better": more cross-disciplinary synergy. ;-) For my part I must admit the current restrictions aren't _that_ irksome: they're just the sort of thing I run into every so often, have to remind myself they're the way they are, and end up writing a few more instance declarations by hand than I initially imagined I 'ought' to have to. On the point of complexity: it's not immediately obvious to me that (setting aside the Hugs-style extension to H98 in the form of the instance decls.) it would cause any blowup here in principle. Granted there's a combinatorial issue, but the breadth and depth of alternatives are necessarily finite, so it seems finitely bound overall, and since HM typing is D-Exp anyway, I'd be surprised if it made it worse than that in toto. Hideousness of implementation's another matter, and certainly I don't want to be biting the hand that feeds... Cheers, Alex.