[GHC] #12418: Make `MonadCont (ContT r m)` polykinded (r::k), (m::k -> Type)

[GHC]

#12418: Make `MonadCont (ContT r m)` polykinded (r::k), (m::k -> Type)
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Core Libraries    |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Iceland_jack):

 Without the kind the error was also confusing

 {{{
     • No instance for (MonadCont (ContT r1 m1))
         arising from a use of ‘callCC’
     • In the expression:
           callCC :: ((a -> ContT r m b) -> ContT r m a) -> ContT r m a
 }}}

 It took me a while to recognize it was a ''kind'' problem, the instance
 certainly seems to be there!

 {{{#!hs
 instance MonadCont (ContT r m)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12418#comment:2>
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