On Wed, Feb 08, 2006 at 05:48:24PM -0000, Simon Peyton-Jones wrote: > | > b) A pattern type signature may bring into scope a skolem bound > | > in the same pattern: > | > data T where > | > MkT :: a -> (a->Int) -> T > | > f (MkT (x::a) f) = ... > | > > | > The skolem bound by MkT can be bound *only* in the patterns that > | > are the arguments to MkT (i.e. pretty much right away). > [...] > f (MkT (x::a) (f::a->Int)) = ... > > You can imagine that either (a) both bind 'a' to the skolem, but must do > consistently; or (b) that (x::a) binds 'a', and (f::a->Int) is a bound > occurrence. It doesn't matter which you choose, I think.
Another possibility would be to allow an optional explicit quantifier before the data constructor, mirroring the old datatype syntax for existentials: data T = forall a. MkT a (a->Int) f (forall a. MkT x f) = ... _______________________________________________ Haskell-prime mailing list Haskell-prime@haskell.org http://haskell.org/mailman/listinfo/haskell-prime