#9123: Need for higher kinded roles -------------------------------------+------------------------------------- Reporter: simonpj | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.8.2 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Project (more Type of failure: | than a week) None/Unknown | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by simonpj): Replying to [comment:31 goldfire]:
If, instead, we quantified over the leftover implication, we'd be done, with an inferred implication constraint.
Not a good plan. I'm sure you can't be saying * Reject a constraint `C a Int` as "exotic" * Accept a constraint `forall a. C a Int` as fine When would an implication be "exotic"? I think it'd be much better to ask the user to use standalone deriving and write the constraint; but that's going to be jolly scary for users who just want `deriving( Monad )`. Your point that it only affects monad transformers is a good one though. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9123#comment:32 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler