#13971: Misleading "Kind mis-match on LHS of default declaration" error -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): What's curious is that in other situations, the error message you get for mismatched kinds in type family defaults is much clearer. For instance: {{{ λ> class C a where { type T a; type T a = 4 } <interactive>:1:40: error: • Expected a type, but ‘4’ has kind ‘GHC.Types.Nat’ • In the type ‘4’ In the default type instance declaration for ‘T’ In the class declaration for ‘C’ }}} That is much, much better than the vague "Kind mis-match on LHS of default declaration" message we get in the original program. I wonder if GHC can arrange for this "Expected a type, but `foo` has kind `Bar`" error message to trigger for the original program as well. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13971#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler