#9376: More informative error messages when closed type families fail to simplify -------------------------------------+------------------------------------- Reporter: | Owner: MikeIzbicki | Status: new Type: feature | Milestone: request | Version: 7.8.2 Priority: normal | Keywords: Component: Compiler | Architecture: Unknown/Multiple (Type checker) | Difficulty: Unknown Resolution: | Blocked By: Operating System: | Related Tickets: Unknown/Multiple | Type of failure: | None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by rwbarton): To get the desired behavior in the original program you should help GHC out a little by factoring out the common part of the two constraints. {{{ type OrdRec (f :: * -> *) a b = ( Ord a, Ord b, OrdRec' f a b ) type family OrdRec' (f :: * -> *) a b :: Constraint where OrdRec' f a (f b) = OrdRec f a b OrdRec' f a b = () }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9376#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler