#8084: Enabling PolyKinds makes some type errors weird --------------------------------------------+------------------------------ Reporter: MartijnVanSteenbergen | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by MartijnVanSteenbergen): Ah, the messages make more sense now. It took me a while to see how to read those types. So, to make sure I understand everything correctly, the kinds are as follows: {{{ Any :: forall k. (k -> *) -> * X :: forall k. k -> * Y :: * -> * Z :: Bool -> * }}} And whenever a kind has a forall in it, GHC shows how it instantiated that kind variable. As for preference, I can imagine that having this information is very valuable, but I think it's confusing to use notation that is indistinguishable from normal type application. So something like `Any {*} Y` would help. I also think it would help if the User's Guide explained that GHC shows this extra information, with Simon's example of when this information is needed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8084#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler