[GHC] #7908: InstanceSigs suggestion not accepted

[GHC]

#7908: InstanceSigs suggestion not accepted
-----------------------------+----------------------------------------------
Reporter:  heisenbug         |          Owner:                  
    Type:  bug               |         Status:  new             
Priority:  normal            |      Component:  Compiler        
 Version:  7.7               |       Keywords:                  
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
 Failure:  None/Unknown      |      Blockedby:                  
Blocking:                    |        Related:                  
-----------------------------+----------------------------------------------
 Attached testcase compiles, but when
 uncommenting either of the lines 19, 21 or 23,
 I get an error:

 {{{
 pr7908.hs:23:12:
     Method signature does not match class; it should be
       (>>-) :: forall (c :: k -> *) d.
                Hidden k c -> (forall (a :: k). c a -> d) -> d
     In the instance declaration for `Monad' k (Hidden k)'
 Failed, modules loaded: none.
 }}}

 But in fact I basically copied the suggestion into my file! (with slight
 modification "Hidden k c" --> "Hidden c")

 This may be because of the rank2 type or because of the polykinds
 appearing.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7908>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler