#13328: Foldable, Functor, and Traversable deriving handle phantom types badly -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.1 Component: Compiler | Version: 8.1 Resolution: | Keywords: deriving-perf Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): The role annotation should (I believe) only affect instances derived outside the module. So I believe the concern would be for a type that is defined ''using'' a type defined in another module that has a role annotation. But again, that matches the "what the user would likely write by hand" scenario: we can only do as well as the user could. Yes, it's true that this introduces some potential for surprises; the user won't get a nice error message when they make the change. Do you think this is a judgement call that should be made through the proposal process? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13328#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler