#8950: Typeable instances for promoted lists and tuples -------------------------------------+------------------------------------ Reporter: kosmikus | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: libraries/base | Version: 7.8.1-rc2 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): OK, well, I got sucked into this and spent a couple of hours refactoring `TcDeriv` (again). Man, if I had a pound for each hour I've spent on `deriving`, I'd be a rich bunny. Anyway, the design I have implemented is this: * If you say `AutoDeriveTypeable`, and you do not manually derive `Typeable`, then it's done automatically. * If you derive `Typeable` with `DataKinds` enabled, then you also get `Typeable` instances for the promoted data constructors. * For a data/newtype declared in this module, there is no difference between * putting `Typeable` in the `deriving` clause on a data type declaration * using standalone `deriving instance Typeable T` * However, standalone `deriving` can also derive `Typeable` for * imported types * data families * `AutoDeriveTypeable` derives `Typeable` for * all data/newtypes * all data families * all classes declared in this module. Indeed `AutoDeriveTypeable` is currently the ''only'' way to derive `Typeable` for classes. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8950#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler