#9017: Confusing error message with PolyKinds -------------------------------------+------------------------------------- Reporter: edsko | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler (Type | Version: 7.8.2 checker) | Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | polykinds/T9017 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by goldfire): * testcase: => polykinds/T9017 * status: new => closed * resolution: => fixed Comment: This test case still produces a suboptimal message: {{{ T9017.hs:8:7: error: • Couldn't match kind ‘k’ with ‘*’ ‘k’ is a rigid type variable bound by the type signature for: foo :: forall k k1 (a :: k1 -> k -> *) (b :: k1) (m :: k1 -> k). a b (m b) at T9017.hs:7:8 When matching the kind of ‘a’ • In the expression: arr return In an equation for ‘foo’: foo = arr return • Relevant bindings include foo :: a b (m b) (bound at T9017.hs:8:1) T9017.hs:8:7: error: • Couldn't match kind ‘k1’ with ‘*’ ‘k1’ is a rigid type variable bound by the type signature for: foo :: forall k k1 (a :: k1 -> k -> *) (b :: k1) (m :: k1 -> k). a b (m b) at T9017.hs:7:8 When matching the kind of ‘a’ • In the expression: arr return In an equation for ‘foo’: foo = arr return • Relevant bindings include foo :: a b (m b) (bound at T9017.hs:8:1) }}} We get two duplicate messages, and it's still quite hard to see what's going on. Actually, a little more thought tells me the messages aren't quite duplicates: the kind-generalized type signature contains two different kind variables, both of which are distinct from `*`. With the type signature given, I think it's OK. I'm going to accept this output, but shout if you see a way to improve. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9017#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler