On Tue, Feb 21, 2006 at 07:13:17PM -0800, [EMAIL PROTECTED] wrote: > I'm afraid that may still be insufficient, as the following > counter-example shows. It causes GHC 6.4.1 to loop in the typechecking > phase. I haven't checked the latest GHC.
The HEAD is more cautious: F.hs:12:0: Variable occurs more often in a constraint than in the instance head in the constraint: E m a b (Use -fallow-undecidable-instances to permit this) In the instance declaration for `Foo m (a -> ())' This is required for all instances. GHC 6.4 relaxed it in the presence of FDs on the classes in the context, but as you've shown that is dangerous. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe