[GHC] #9858: Typeable instances should be kind-aware

[GHC]

#9858: Typeable instances should be kind-aware
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        Reporter:  dreixel           |                   Owner:  dreixel
            Type:  bug               |                  Status:  new
        Priority:  highest           |               Milestone:  7.10.1
       Component:  Compiler          |                 Version:  7.9
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by int-e):

 Replying to [comment:33 oerjan]:
 > But anyway, here it is, sort of working, but with some obvious
 drawbacks:

 One such drawback is that the `Kindable'` constraint is sort of
 infectious. One can using a type family for mapping kinds to types, which
 seems to overcome that particular shortcoming:

 {{{
 type family KindRep (p :: k)

 data Star deriving Typeable
 type instance KindRep (Proxy :: * -> *) = Star
 type instance KindRep (Proxy :: (k -> k') -> *) = KindRep (Proxy :: k ->
 *) -> KindRep (Proxy :: k' -> *)

 -- some data kinds: () and []
 type instance KindRep (Proxy :: () -> *) = ()
 type instance KindRep (Proxy :: [k] -> *) = [KindRep (Proxy :: k -> *)]
 }}}

 One could then have

 {{{
 instance Typeable (KindRep (Proxy :: k -> *)) => Typeable' (Proxy :: k ->
 *)
 }}}

 Here's some working code: http://lpaste.net/4263409010180358144

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9858#comment:34>
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