|Version 1 (modified by john@…, 10 years ago) (diff)|
allow extensential type synonyms, so if you had something like the following,
data Type a = ....
you could declare a synonym such as
type AnyType = exists a . Type a
so you can create functions such as
areSame :: AnyType -> AnyType -> Bool
which would expand to
areSame :: forall a b . Type a -> Type b -> Bool
this is not to be confused with the currently allowed in ghc
type AllTypes = forall a . Type a oddFunc :: AllTypes -> AllTypes -> Bool
which expands to the rank 2 type
oddFunc :: (forall a . Type a) -> (forall b . Type b) -> Bool
which means something quite different.
- if we use 'exists' for existential types, this seems like a natural use of said keyword too.