#8165: Use GeneralizedNewtypeDeriving to automatically create associated type families -------------------------------------+------------------------------------- Reporter: MikeIzbicki | Owner: goldfire Type: feature request | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler (Type | Version: 7.6.3 checker) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by goldfire): * owner: => goldfire * milestone: => 7.12.1 Comment: Encouraged by Iavor Diatchki and Adam Gundry, I've realized that my comment:4 is utterly wrong -- !MikeIzbicki's proposal is reasonable. Concretely, I propose: * `GeneralizedNewtypeDeriving` for classes with associated types define new associated type instances that "look through" to the underlying type instance. This satisfies Mike's original example. To my comment:1, it says `Int`. And, this proposal works for comment:3. Note that associated `data` instances will still be prohibited -- these are not covered by this ticket. I can implement in due course. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8165#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler