[GHC] #12432: TypeInType: open type family application as type family return kind fails to compile

[GHC]

#12432: TypeInType: open type family application as type family return kind fails
to compile
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           Reporter:  j6carey        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
  (Type checker)                     |
           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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 With TypeInType enabled, I can use a closed type family to compute the
 return kind of a type family from its arguments.  But an equivalent open
 type family used in the same way triggers a compilation failure, as if the
 relevant instance of that open type family were not considered.  (Of
 course, there may be some subtle prohibition of which I am not aware at
 the present time.)  I will attach a test case.

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