#9123: Need for higher kinded roles -------------------------------------+------------------------------------ Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by ekmett): True, if you keep the existing role rules that works for the concrete choice of (,) and State works. Consider a parameterized version where we fuse the two parameters into arguments of the same type argument, but don't make it concrete. e.g. {{{ newtype Foo s p a = Foo (s -> p a s) }}} and there you get stuck on GND for `a` whether or not you keep the existing role-based machinery for lifting coercions. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9123#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler