Why can I not define the following (in ghc): > class Foo p where > instance Foo Double where > foo :: Double -> (forall q . Foo q => q) > foo p = p
>From my humble (lack of) knowledge, there seems to be nothing wrong here, but ghc (5.03) complains about unifying q with Double. I *can* write: > class Foo p where > instance Foo Double where > data T = forall q . Foo q => T q > foo :: Double -> T > foo p = T p which is very similar, except that the explicit universal quantification is happening in in the datatype and not the function type. why is the former disallowed? -- Hal Daume III "Computer science is no more about computers | [EMAIL PROTECTED] than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume _______________________________________________ Glasgow-haskell-users mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
