[GHC] #9633: PolyKinds in 7.8.2 vs 7.8.3

[GHC]

#9633: PolyKinds in 7.8.2 vs 7.8.3
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              Reporter:  crockeea    |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:  PolyKinds
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:  GHC         |       Blocked By:
  rejects valid program              |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by crockeea):

 I verified that adding `TypeFamilies` to Foo.hs in 7.8.3 makes the
 original example compile fine. I'm happy with the error in HEAD, so it
 looks like this problem will not be an issue in 7.10. Thanks for
 investigating Simon!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9633#comment:9>
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