#14451: Need proper SCC analysis of type declarations, taking account of CUSKs -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeInType, | CUSKs Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #7503 | Differential Rev(s): Wiki Page: | https://ghc.haskell.org/trac/ghc/wiki/GhcKinds/KindInference| -------------------------------------+------------------------------------- Comment (by RyanGlScott): Amazingly, the original program in this ticket (including the `Comp f g a = f · (g · a)` tweak): {{{#!hs {-# Language KindSignatures, TypeOperators, PolyKinds, TypeOperators, ConstraintKinds, TypeFamilies, DataKinds, TypeInType, GADTs, AllowAmbiguousTypes, InstanceSigs, RankNTypes, UndecidableInstances #-} import Data.Kind data TyFun :: Type -> Type -> Type type a ~> b = TyFun a b -> Type type Cat ob = ob -> ob -> Type type family Apply (f :: a ~> b) (x :: a) :: b where Apply (CompSym2 f g) a = Comp f g a data CompSym2 :: (b ~> c) -> (a ~> b) -> (a ~> c) type a·b = Apply a b 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 (f·a) (f·a') type family Comp (f::k1 ~> k) (g::k2 ~> k1) (a::k2) :: k where Comp f g a = f · (g · a) }}} Appears to have fixed itself at some point between GHC 8.4 and 8.6, since it typechecks on GHC 8.6.2 and HEAD. I'm not sure what commit caused that, but that's cool nonetheless. Let me check to see if the same miracle happened to #7503. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14451#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler