[GHC] #9612: Use functional dependencies to give more specific error messages

[GHC]

#9612: Use functional dependencies to give more specific error messages
-------------------------------------+-------------------------------------
              Reporter:  rwbarton    |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Compiler    |         Keywords:
  (Type checker)                     |     Architecture:  Unknown/Multiple
            Resolution:              |       Difficulty:  Unknown
      Operating System:              |       Blocked By:
  Unknown/Multiple                   |  Related Tickets:
       Type of failure:              |
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------

Comment (by rwbarton):

 Oh, I meant for `tell` to be the one from mtl `Control.Monad.Writer`,
 sorry.
 {{{
 class (Monoid w, Monad m) => MonadWriter w m | m -> w where
     writer :: (a,w) -> m a
     tell   :: w -> m ()
     listen :: m a -> m (a, w)
     pass   :: m (a, w -> w) -> m a
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9612#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler