| 1 | allow extensential type synonyms, so if you had something like the |

| 2 | following, |

| 3 | {{{ |

| 4 | data Type a = .... |

| 5 | }}} |

| 6 | you could declare a synonym such as |

| 7 | {{{ |

| 8 | type AnyType = exists a . Type a |

| 9 | }}} |

| 10 | so you can create functions such as |

| 11 | {{{ |

| 12 | areSame :: AnyType -> AnyType -> Bool |

| 13 | }}} |

| 14 | |

| 15 | which would expand to |

| 16 | {{{ |

| 17 | areSame :: forall a b . Type a -> Type b -> Bool |

| 18 | }}} |

| 19 | |

| 20 | this is not to be confused with the currently allowed in ghc |

| 21 | {{{ |

| 22 | type AllTypes = forall a . Type a |

| 23 | |

| 24 | oddFunc :: AllTypes -> AllTypes -> Bool |

| 25 | |

| 26 | }}} |

| 27 | which expands to the rank 2 type |

| 28 | {{{ |

| 29 | oddFunc :: (forall a . Type a) -> (forall b . Type b) -> Bool |

| 30 | }}} |

| 31 | |

| 32 | which means something quite different. |

| 33 | |

| 34 | Pro |

| 35 | |

| 36 | * if we use 'exists' for existential types, this seems like a natural use of said keyword too. |