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{-# LANGUAGE MagicHash #-}
-- It used to be that (->) would have a very restrictive kind when used in
-- prefix position. This restriction was lifted after the levity polymorphism
-- work in 2016.
module ShouldSucceed where
import GHC.Base
type T = (->) Int#
-- Here's the old comment from TypeRep:
--
-- funTyCon = mkFunTyCon funTyConName
-- (mkArrowKinds [liftedTypeKind, liftedTypeKind]
-- liftedTypeKind)
-- You might think that (->) should have type (? -> ? -> *), and you'd be right
-- But if we do that we get kind errors when saying
-- instance Control.Arrow (->)
-- because the expected kind is (*->*->*). The trouble is that the
-- expected/actual stuff in the unifier does not go contra-variant, whereas
-- the kind sub-typing does. Sigh. It really only matters if you use (->) in
-- a prefix way, thus: (->) Int# Int#. And this is unusual.
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