[GHC] #14190: Typeable imposes seemingly redundant constraints on polykinded instances

[GHC]

#14190: Typeable imposes seemingly redundant constraints on polykinded instances
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        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler (Type    |              Version:  8.2.1
  checker)                           |
      Resolution:                    |             Keywords:  Typeable
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 bgamari):

 Regarding comment:7,

 I'm not sure how easy it would be to implement this. Goldfire will need to
 comment here, but it seems like this may be hard as there is nothing tying
 `k` back to `a`. One way of hacking around this might be to add `Typeable
 k` evidence to the solved dictionary cache every time we solve for
 `Typeable (a :: k)`. However, this would lead to the production of lots of
 redundant evidence and just feels terribly wrong.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14190#comment:8>
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