#12553: Reference kind in a type instance declaration defined in another instance declaration -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Interesting! this works {{{#!hs class Syntactic a where type Domain a :: Sig u -> Type type Internal a :: u a :: Proxy (Domain a) b :: Proxy (Internal a) -- c :: AST (Domain a) (Full (Internal a)) }}} but for some reason the method `c` breaks it. ---- Functional dependencies solve this, but they change the API in a way that doesn't work for me: {{{#!hs class Syntactic a (dom :: Sig u -> Type) | a -> dom where type Internal a :: u desugar :: ASTF dom (Internal a) -> a sugar :: a -> ASTF dom (Internal a) instance Syntactic (AST dom (Full a)) dom where type Internal (AST dom (Full a)) = a desugar = id sugar = id }}} ---- Here is another workaround, it's not perfect (need to recover `Domain`, `Internal`) but it's a start {{{#!hs class Syntactic a where type DomainInternal a :: Type desugar :: DomainInternal a -> a sugar :: a -> DomainInternal a instance Syntactic (AST dom (Full a)) where type DomainInternal (AST dom (Full a)) = AST dom (Full a) desugar x = x sugar x = x }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12553#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler