#9612: Use functional dependencies to give more specific error messages -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: feature | Status: closed request | Milestone: Priority: normal | Version: 7.8.3 Component: Compiler | Keywords: (Type checker) | Architecture: Unknown/Multiple Resolution: fixed | Difficulty: Unknown Operating System: | Blocked By: Unknown/Multiple | Related Tickets: Type of failure: | None/Unknown | Test Case: | typecheck/should_fail/T9612 | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => closed * testcase: => typecheck/should_fail/T9612 * resolution: => fixed Comment: Good idea, thank you. The error message is now {{{ T9612.hs:16:9: Couldn't match type ‘[(Int, a)]’ with ‘(Int, a)’ arising from a functional dependency between: constraint ‘MonadWriter (Int, a) (WriterT [(Int, a)] Identity)’ arising from a use of ‘tell’ instance ‘MonadWriter w (WriterT w m)’ at T9612.hs:20:10-59 }}} Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9612#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler