#8631: Need ImpredicativeTypes for GeneralizedNewtypeDeriving? -------------------------------------+------------------------------------ Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 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 goldfire): Yes, absolutely, explicit type application would make all of this much easier. But, I believe we can still fix this bug without it, once we have some design decisions about the questions I posed originally. As for question 1: I think it's safe to turn on !ImpredicativeTypes over the code produced by GND. This would make using GND easier, and I don't want to bother users with this technicality. As for question 2: In general, I'm a little worried about error messages that mention `coerce` yet refer to code that patently does ''not'' mention `coerce`. If we can't get rid of the `coerce`, could we add some extra context describing the use of GND and perhaps suggesting `-ddump-deriv`? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8631#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler