Already in GHC, and describe in our paper on scoped type variables: http://research.microsoft.com/~simonpj/papers/scoped-tyvar Simon | -----Original Message----- | From: Ashley Yakeley [mailto:ashley@semantic.org] | Sent: 11 April 2002 12:11 | To: Haskell List | Subject: More Haskell Blue Sky: Partial Type Annotations | | | I sometimes come across a situation when I only want to provide a | _partial_ type annotation, perhaps because the full type has some | variable unified with some variable in some other type annotation, or | something. For instance: | | f :: forall a. [a] -> [a] -> [a] | f x y = g x where | g [] = y | g (_:_) = x | | ...there doesn't seem to be a way of giving a type annotation | for 'g'. | Theoretically it's '[a] -> [a]', but where 'a' is the same as | the 'a' in | the type signature for 'f'. | | Under this proposal, unqualified type variables would be | considered to be | 'free' rather than implicitly forall-qualified. So for instance, any | function could be given the partial type annotation 'a -> b'. For | instance, all these annotations would be the same given this function: | | k :: a | k :: a -> ba | k :: a -> b -> a | k :: forall b. a -> b -> a | k :: forall a b. a -> b -> a | | k x y = x | | ...and these would both be the same, but different from the previous: | | k' :: Int -> ba | k' :: forall b. Int -> b -> Int | | k' x y = x | | And so we could write this: | | f :: forall a. [a] -> [a] -> [a] | f x y = g x where | g :: [a] -> [a] -- partial annotation may be sufficient | g [] = y | g (_:_) = x | | I admit that's a bit of a change, and might break programs... In | addition, it doesn't address the occasional need to tie type | annotations | together, something that has often made me add ugly dummy | arguments used | just for their type. | | -- | Ashley Yakeley, Seattle WA | | _______________________________________________ | Haskell mailing list | Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell |