| > I can then say: | > | > > bar :: C a => a -> Int | > > bar (x :: a) = foo (undefined :: a) | > | > But not: | > | > > bar :: C a => a -> Int | > > bar x = foo (undefined :: a) | > | > because it tries to use a new scope for the type variable a and | > doesn't unify it with the one in the type spec. Why not? | | I don't know why it isn't the case in Haskell. | In Mercury we do allow type variables in function type | declarations to scope over explicit type qualifications in | clause bodies.
It's a deliberate design choice, but certainly only one of taste. It seems a bit odd for a type signature (perhaps separated by a long way from the definition) should bind a type variable that scopes over the function body. Mark Shields and I are writing a paper about the scoped-type-variable design in GHC; we'll discuss this point. Simon _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
