[GHC] #9376: More informative error messages when closed type families fail to simplify

[GHC]

#9376: More informative error messages when closed type families fail to simplify
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              Reporter:              |            Owner:
  MikeIzbicki                        |           Status:  new
                  Type:  feature     |        Milestone:
  request                            |          Version:  7.8.2
              Priority:  normal      |         Keywords:
             Component:  Compiler    |     Architecture:  Unknown/Multiple
  (Type checker)                     |       Difficulty:  Unknown
            Resolution:              |       Blocked By:
      Operating System:              |  Related Tickets:
  Unknown/Multiple                   |
       Type of failure:              |
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 Is the test for rhss-unify important?  How bad would it be if the
 compatibility check ignored the RHS?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9376#comment:4>
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