[GHC] #10524: PolyKinds doesn't interact well with DeriveFunctor

[GHC]

#10524: PolyKinds doesn't interact well with DeriveFunctor
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        Reporter:  RyanGlScott       |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:  #10561            |  Differential Revisions:
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Comment (by simonpj):

 OK, so I fixed comment:7.  But the original bug report remains
 {{{
 newtype Compose f g a = Compose (f (g a)) deriving Functor
 }}}
 should be fine, but elicits
 {{{
 T10524.hs:5:52: error:
     Couldn't match kind ‘k’ with ‘*’
       arising from the first field of ‘Compose’ (type ‘f (g a)’)
     When deriving the instance for (Functor (Compose f g))
 }}}
 After all, this explicit instance declaration typechecks fine
 {{{
 instance (Functor f, Functor g) => Functor (Compose f g) where
   fmap fn (Compose x) = Compose (fmap (fmap fn) x)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10524#comment:11>
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