I was wondering if this would make sense 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 opposed to 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 might be another useful use of said name. John -- John Meacham - ⑆repetae.net⑆john⑈