#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 goldfire): I think the desired behavior here is up for debate. When I first started with `-XPolyKinds`, I thought the messages were strange, too. Now that I use it a lot, I find the explicit kind parameters really helpful (except in type-level lists!). Perhaps the principled approach would be to omit kind applications by default but enable them with a flag like `-fshow- explicit-kind-apps`. Seeing the kind applications also helps to teach the programmer more of what is going on under the hood. Sometimes, it is necessary to be thinking about the implicit kind parameters to make sense of a program, particularly with kind-polymorphic type families. For some examples where the type families only make sense when thinking about explicit kind application, see the discussion for #7939. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8084#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler