{-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE UnboxedTuples #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE MagicHash #-} module Bug where import GHC.Exts (TYPE, RuntimeRep, Weak#, State#, RealWorld, mkWeak# ) class Foo (a :: TYPE rep) where bar :: forall rep2 (b :: TYPE rep2). (a -> a -> b) -> a -> a -> b baz :: forall rep (a :: TYPE rep). Foo a => a -> a -> (# a, a #) baz = bar (#,#) obscure :: (forall (rep1 :: RuntimeRep) (rep2 :: RuntimeRep) (a :: TYPE rep1) (b :: TYPE rep2). a -> b -> (# a, b #)) -> () obscure _ = () quux :: () quux = obscure (#,#) primop :: forall (rep :: RuntimeRep) (a :: TYPE rep) b c. a -> b -> (State# RealWorld -> (# State# RealWorld, c #)) -> State# RealWorld -> (# State# RealWorld, Weak# b #) primop = mkWeak#