[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):

 Replying to [comment:7 ekmett]:
 > @Iceland_jack, I'm sorry, but would you object terribly strongly to that
 resolution?

 I would not, I didn't expect such far-reaching implications.

 {{{#!hs
 label :: ContT r m (ContT r m a)
 label = callCC $ \k -> [ m | let m = k m ]
 }}}

 It's unfortunate that `↑` doesn't type check with `PolyKinds` and that the
 inferred type of `↓` doesn't either, that's somewhat rare

 {{{#!hs
 -- foo :: Cont r m a
 foo = do
   l <- label
   l
 }}}

 but seems like it can't be helped.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12418#comment:8>
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