#10836: Better error reporting for closed type families -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Incorrect | Test Case: warning at compile-time | typecheck/should_fail/T10836 Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by jstolarek): Simon, this change is a huge improvement over the previous situation, but not everything is yet perfect. Consider this: {{{#!hs type family FClosed a b c = (result :: *) | result -> a b c where FClosed Int Char Bool = Bool FClosed Char Bool Int = Int FClosed Bool Int Char = Int type family Bar a = r | r -> a where Bar Int = Bool Bar Bool = Int Bar Bool = Char bar :: Bar a -> Bar a bar x = x barapp :: Char barapp = bar 'c' }}} I would expect to get two errors: {{{ T6018.hs:8:5: error: Type family equations violate injectivity annotation: FClosed Char Bool Int = Int FClosed Bool Int Char = Int In the equations for closed type family ‘FClosed’ In the type family declaration for ‘FClosed’ T6018.hs:20:14: error: Couldn't match expected type ‘Bar a0’ with actual type ‘Char’ The type variable ‘a0’ is ambiguous In the first argument of ‘bar’, namely ‘'c'’ In the expression: bar 'c' In an equation for ‘barapp’: barapp = bar 'c' }}} But I only get the first one. Is this expected? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10836#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler