#15515: Bogus "No instance" error when type families appear in kinds -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler (Type | Version: 8.4.3 checker) | Keywords: TypeInType, Resolution: | TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): The class instance should be rejected -- indeed, I'm quite surprised it's not. Let's write with explicit kinds: {{{#!hs class C k a where ... instance C (F -> Type) D where ... }}} That instance mentions a type family in one of its arguments, which should be rejected. I would love to come up with a way where we ignore determined dependent arguments during matching, which would then allow this instance to work, but we're not there yet. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15515#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler