[GHC] #9123: Need for higher kinded roles

[GHC]

#9123: Need for higher kinded roles
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        Reporter:  simonpj           |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.8.2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by ekmett):

 Hrmm, when we have something like

 {{{
 newtype F p f a = F { runF :: p a  (f (F p f a)) }
 }}}

 do we get stuck again because of the fact that p has two args and the
 coercion of a has to be used on both sides of it?

 {{{
 Free = F (,)
 Cofree = F Either
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9123#comment:18>
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