#8560: undeducable Typeable error with data kinds when deriving Data for GADT in GHC version 7.7.20131122 -------------------------------------+------------------------------------ Reporter: carter | 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 simonpj): I have not even begun to think what `deriving( Data )` might do for GADTs. At Lennart's request, we did make "standalone deriving" simply generate code, and if it doesn't typecheck it's your problem. See [http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html #stand-alone-deriving the manual] (fourth bullet). See #3102, and #3702 for someone who liked it. I'm not sure that was a good decision, especially for jolly complicated classes like `Data`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8560#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler