#9376: Recursive closed type families fails -------------------------------------+------------------------------------- Reporter: | Owner: MikeIzbicki | Status: new Type: bug | Milestone: Priority: normal | Version: 7.8.2 Component: Compiler | Keywords: (Type checker) | Architecture: Unknown/Multiple Resolution: | Difficulty: Unknown Operating System: | Blocked By: Unknown/Multiple | Related Tickets: Type of failure: | None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by kosmikus): Replying to [comment:1 simonpj]: Simon, your non-recursive version says:
type family OrdRec (f :: * -> *) a b :: Constraint where OrdRec f a (f b) = ( Ord a, Ord (f b), Ord (f b) ) OrdRec f a b = ( Ord a, Ord b )
which indeed fails, but with
type family OrdRec (f :: * -> *) a b :: Constraint where OrdRec f a (f b) = ( Ord a, Ord (f b) ) OrdRec f a b = ( Ord a, Ord b )
it compiles. Does GHC somehow recognize that the first line is a special- case of the second? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9376#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler