[GHC] #12432: Use kind equality in instance context in type family instance

[GHC]

#12432: Use kind equality in instance context in type family instance
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        Reporter:  j6carey           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by kosmikus):

 Haven't checked the attached test cases in detail, but from the
 description and discussion it sounds as if the original issue is #12381,
 which is fixed in HEAD. And the subsequent issue seems to be #12384, which
 is not fixed and seems to be difficult to fix.

 I ran into both of those issues when I tried to write a type-level
 translation of the new type-level generic metadata that GHC 8 provides
 into a different representation of type-level metadata that would be
 useful for generics-sop (and makes use of a type-level GADT and therefore
 TypeInType).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12432#comment:9>
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