[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:              |  Operating System:  Unknown/Multiple
Differential Revisions:  Phab:D69    |   Type of failure:  None/Unknown
          Architecture:              |         Test Case:
  Unknown/Multiple                   |          Blocking:
            Difficulty:  Unknown     |
            Blocked By:              |
       Related Tickets:  #1241,      |
  #2247, #8356, #9103, #9227         |
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Comment (by sulzmann):

 Regarding dropping the Consistency Condition (comment:41)

 Well, that's the minimal requirement I demand to call something Functional
 Dependencies. Oh, I see we are in the DysfunctionalDependencies world :)
 I'm also more than curious how to establish type safety without this
 requirement.

 What I'm describing in comment:33 are various forms of (type safe)
 Functional Dependencies where 'predictability' of type inference decreases
 the more we relax the coverage criteria.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8634#comment:44>
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