[GHC] #11715: There's something fishy going on with Constraint

[GHC]

#11715: There's something fishy going on with Constraint
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |
      Resolution:                    |             Keywords:
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 simonpj):

 NB: as things stand, from `axC` we could deduce `Constraint ~N *`, which
 we definitely don't want.

 To solve this we could restrict the coercion language a little, so that
 you can't extract a kind equality from a representational type equality.
 (This might be good anyway.  It's weird that you can currently get a
 ''nominal'' kind equality from a ''representational'' type equality.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11715#comment:7>
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