Yes, GHC also uses `cast` to express the coercion for a newtype. A type class with just one method is represented by a newtype. Nothing to do with FDs; this is two source-language constructs using the same intermediate-language encoding. (Though using casts for newtype did give rise to an unexpected interaction that I have yet to sort out! http://hackage.haskell.org/trac/ghc/ticket/1496)
Simon | -----Original Message----- | From: Remi Turk [mailto:[EMAIL PROTECTED] | Sent: 20 October 2007 21:25 | To: Simon Peyton-Jones | Cc: glasgow-haskell-users@haskell.org; Jean-Philippe Bernardy | Subject: Re: type families not advertised for 6.8 | | On Fri, Oct 19, 2007 at 08:25:22AM +0100, Simon Peyton-Jones wrote: | > | What does this imply for 6.8 support for FD's, as they now use | > | the same type-coercions? | > | > Actually FDs do not use type coercions, in GHC at least. As Mark | | Excuse me, it turns out I didn't look carefully enough: It's not | functional dependencies, it's classes-with-only-one-method: | | module Bar where | | bar = fmap id [] | | Compiles to the following Core with 6.8.0.20071002: | | Bar.bar :: forall a_a5M. [a_a5M] | [GlobalId] | [] | Bar.bar = | \ (@ a_a5M) -> | (GHC.Base.$f8 | `cast` ((GHC.Base.:Co:TFunctor) [] | :: (GHC.Base.:TFunctor) [] | ~ | forall a_a5G b_a5H. (a_a5G -> b_a5H) -> [a_a5G] -> [b_a5H])) | @ a_a5M @ a_a5M (GHC.Base.id @ a_a5M) (GHC.Base.[] @ a_a5M) | | | Or does this simply mean that only type-functions (the type/axiom | stuff) is not supported in 6.8, but type coercions (~ and cast) are supported | (although perhaps not at the source level)? _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
