[GHC] #9580: Possible excessive leniency in interaction between coerce and data families?

[GHC]

#9580: Possible excessive leniency in interaction between coerce and data
families?
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              Reporter:  dmcclean    |            Owner:  simonpj
                  Type:  bug         |           Status:  closed
              Priority:  low         |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
  (Type checker)                     |         Keywords:
            Resolution:  fixed       |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:  indexed-    |
  types/should_fail/T9580            |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 Cam you give a concrete example?  And compare with whatever
 [http://research.microsoft.com/en-us/um/people/simonpj/papers/ext-f/ the
 paper] says?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9580#comment:7>
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