#14450: GHCi spins forever -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: TypeInType, | Operating System: Unknown/Multiple PolyKinds | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code compiles just fine (8.3.20170920) {{{#!hs {-# Language KindSignatures, TypeOperators, PolyKinds, TypeOperators, ConstraintKinds, TypeFamilies, DataKinds, TypeInType, GADTs, AllowAmbiguousTypes, InstanceSigs #-} import Data.Kind data TyFun :: Type -> Type -> Type type a ~> b = TyFun a b -> Type type Cat ob = ob -> ob -> Type type SameKind (a :: k) (b :: k) = (() :: Constraint) type family Apply (f :: a ~> b) (x :: a) :: b where Apply IddSym0 x = Idd x class Varpi (f :: i ~> j) where type Dom (f :: i ~> j) :: Cat i type Cod (f :: i ~> j) :: Cat j varpa :: Dom f a a' -> Cod f (Apply f a) (Apply f a') type family Idd (a::k) :: k where Idd (a::k) = a data IddSym0 :: k ~> k where IddSym0KindInference :: IddSym0 l instance Varpi (IddSym0 :: Type ~> Type) where type Dom (IddSym0 :: Type ~> Type) = (->) type Cod (IddSym0 :: Type ~> Type) = (->) varpa :: (a -> a') -> (a -> a') varpa = id }}} But if you change the final instance to {{{#!hs instance Varpi (IddSym0 :: k ~> k) where type Dom (IddSym0 :: Type ~> Type) = (->) }}} it sends GHC for a spin. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14450 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler