#11719: Cannot use higher-rank kinds with type families -------------------------------------+------------------------------------- Reporter: ocharles | Owner: Type: bug | Status: closed Priority: normal | Milestone: 8.0.1 Component: Compiler (Type | Version: 8.0.1-rc2 checker) | Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | dependent/should_compile/T11719 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: merge => closed * failure: None/Unknown => GHC rejects valid program * resolution: => fixed * milestone: => 8.0.1 @@ -7,1 +7,1 @@ - {{{ + {{{#!hs New description: This ticket came out of a discussion with Richard in this mailing list post: https://mail.haskell.org/pipermail/haskell- cafe/2016-March/123462.html Here's the code that should work, but doesn't: {{{#!hs import Data.Kind data TyFun :: * -> * -> * type a ~> b = TyFun a b -> * type family (f :: a ~> b) @@ (x :: a) :: b data Null a = Nullable a | NotNullable a type family ((f :: b ~> c) ∘ (g :: a ~> b)) (x :: a) :: c where (f ∘ g) x = f @@ (g @@ x) type family BaseType (k :: forall a. a ~> Type) (x :: b) :: Type where -- this fails :( -- BaseType k x = (@@) k x }}} -- Comment: Merged as bae60f654ac5d99834818da9c50ad4bee54c334e. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11719#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler