#10598: DeriveAnyClass and GND don't work well together -------------------------------------+------------------------------------- Reporter: osa1 | Owner: RyanGlScott Type: bug | Status: patch Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Generics Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2280 Wiki Page: | -------------------------------------+------------------------------------- Comment (by oerjan): After reading the ghc-devs discussion that decided to rename `builtin` to `bespoke`, I have a question. Is it still the case that using any other deriving strategy than `bespoke` for a class that supports `bespoke` requires using this new extension? The summary of the new system in the mailing list discussion seemed to imply not in some cases, but that could be just my misunderstanding. If not, then that could lead to confusing errors, like accidentally deriving `Functor` with anyclass because `DeriveAnyClass` is enabled but `DeriveFunctor` has been forgotten, and would probably warrant some more warnings. On the other hand, I think GND would give equivalent result to `bespoke` for many classes, so it might be convenient ''not'' to warn in those cases. E.g. when someone wants to derive `Functor`, `Applicative` and `Monad` for their monad stack newtype, it seems almost reasonable that only GND needs to be enabled, and not `DeriveFunctor`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10598#comment:40 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler