existential-type-synonyms.md

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