#16027: Cannot use DefaultSignatures for TypeFamiles -------------------------------------+------------------------------------- Reporter: Ericson2314 | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: 8.6.3 Component: Compiler | Version: 8.6.2 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): Until constrained type families are implemented (which likely won't be for a good while), you can do this: {{{#!hs class Monad m => MyMonad m where type AssociatedMonad m :: Type -> Type type AssociatedMonad m = DefaultAssociatedMonad m fun :: Foo -> m () default fun :: (m ~ t m', MonadTrans t, MyMonad m') => Foo -> m () fun = lift . fun type family DefaultAssociatedMonad (m :: Type -> Type) :: Type -> Type where DefaultAssociatedMonad (t m') = t (AssociatedMonad m') }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16027#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler