[GHC] #13643: Core lint error with TypeInType and TypeFamilyDependencies

[GHC]

#13643: Core lint error with TypeInType and TypeFamilyDependencies
-------------------------------------+-------------------------------------
        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  InjectiveFamilies, TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #12102            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by goldfire):

 I believe this is the same as #12919, although the symptoms are markedly
 different.

 The problem is that (because flattened types have flattened kinds),
 flattening `T I (False |> co)` (where `co :: Bool ~ Interp I`) yields the
 ill-kinded `T I False`. Instead, we should change the kind invariant on
 flattening to say that flattening does not change a type's kind. Then this
 problem (and #12919) are fixed. I hope.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13643#comment:2>
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