#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 nomeata): It should have been [95ba5d81/ghc]: We check at deriving time that the `Coercible` instances are solvable, and report an appropriate error message; any time that there is an error message mentioning `coercible` (or deriv-generated code in general), that is a bug. So unless turning on `ImpredicativeTypes` for deriv’ed code solve the problem, we need to check for this already at deriving phase, and report an error. What would that error say? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8631#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler