#13731: DeriveFunctor and friends don't understand type families -------------------------------------+------------------------------------- Reporter: spacekitteh | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott):
So it's not that it must be a data type; it can be a saturated type- family application.
Am I missing something? In the original example, the type family instance is: {{{#!hs type instance ExtensionType ListExtension a = [a] }}} And the instance we're deriving is: {{{#!hs deriving instance Functor (Test ListExtension) }}} In other words, the field of `Extend` will have type `ExtensionType ListExtension a`. This is a fully saturated type family application, right? So surely the rule you've proposed doesn't quite capture the essence of this problem. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13731#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler