[GHC] #8634: Relax functional dependency coherence check ("liberal coverage condition")

[GHC]

#8634: Relax functional dependency coherence check ("liberal coverage condition")
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              Reporter:  danilo2     |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:  7.10.1
              Priority:  high        |          Version:  7.7
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:  #1241, #2247,
  None/Unknown                       |  #8356, #9103, #9227
             Test Case:              |
              Blocking:              |
Differential Revisions:  Phab:D69    |
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Comment (by danilo2):

 Goldfire - I would do it as fast as possible. But first I have to solve an
 issue I've got here at the company I'm working at. It is connected to
 injective type families (if I'm not wrong). Anyway it shows, that we
 cannot do something in Haskell, which should be doable in my opinion.

 I would be very thankful if you Goldfire or Simon just look at it and give
 maybe any hints how can we solve it:
 http://stackoverflow.com/questions/25854072/injective-type-families-in-
 haskell

 After solving it I will start working on the tests asap.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8634#comment:56>
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