Bugs item #807249, was opened at 2003-09-16 16:37 Message generated for change (Comment added) made by simonmar You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=108032&aid=807249&group_id=8032
Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: Compiler (Type checker) Group: None Status: Open Resolution: None Priority: 6 Submitted By: Simon Peyton Jones (simonpj) Assigned to: Simon Peyton Jones (simonpj) Summary: Instance match failure on openTypeKind Initial Comment: Consider instance Show (a->b) where ... foo x = show (\ _ -> True) This fails with: No instance for (Show (t -> Bool)) arising from use of `show' at Foo.hs:5 Reason: the type of (\_ -> True) is (t -> Bool) where t has an "openTypeKind". It's possible that the function will be applied to say an Int#, and the openTypeKind records that this is OK. BUT, the instance decl Show (a->b) has a::liftedTypeKind, and that doesn't match an openTypeKind type variable. This bug relates to GHC's unsatisfactory treatment of the variants of kind "type", for which there are at least 2 other SourceForge bugs registered (753780 and 753777). It's very obscure, so I'm not going to fix it today. ---------------------------------------------------------------------- >Comment By: Simon Marlow (simonmar) Date: 2005-07-11 10:36 Message: Logged In: YES user_id=48280 ghci015 now tests for this bug. ---------------------------------------------------------------------- Comment By: Simon Peyton Jones (simonpj) Date: 2005-05-23 12:57 Message: Logged In: YES user_id=50165 I'm bumping up the priority of this bug, because it also happens if, in GHCi, you say Prelude> :m +Text.Show.Functions Text.Show.Functions> print (\x -> x) (this elicits a no-such-instance error) It's even more perplexing that this does not happen if you say > print id becuase 'id' has kind-defaulted type variables in its type. Sigh. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=108032&aid=807249&group_id=8032 _______________________________________________ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs