The "right" solution is, I think, at the bottom of comment:20. But NB
#9858: Typeable instances should be kind-aware -------------------------------------+------------------------------------- Reporter: dreixel | Owner: dreixel Type: bug | Status: new Priority: highest | Milestone: 7.10.1 Component: Compiler | Version: 7.9 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:30 simonpj]: that solution will mean that all these standalone derived instances would become illegal, so there is a backward compatibility cost. The drastic solution does not have this problem. Wouldn't it be (sufficiently) correct to simply ignore all `Typeable` instance declarations (`deriving`, standalone `deriving`, and otherwise), issuing a warning to that effect, instead of rejecting them outright? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9858#comment:39 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler