#8565: New GeneralisedNewtypeDeriving needs help with higher rank types -------------------------------------------------+------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Test Case: | Difficulty: typecheck/should_compile/T8565 | Unknown Blocking: | Blocked By: | Related Tickets: -------------------------------------------------+------------------------- Comment (by goldfire): I just tested this with `ImpredicativeTypes` on, and the error message was from the `Coercible` stuff. With another case in that code (and `ImpredicativeTypes`), I think this would work. The underlying roles machinery is certainly strong enough to handle this case. I'm OK if we require a user to specify `ImpredicativeTypes` for this to work -- it really is impredicative! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8565#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler