[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 request   |                  Status:  new
        Priority:  high              |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.7
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:  #1241, #2247,     |                Blocking:
  #8356, #9103, #9227                |  Differential Revisions:  Phab:D69
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Comment (by simonpj):

 > Is there a wiki page or similar describing the meaning of functional
 dependencies under `DysfunctionalDependencies`?

 See the end of comment:14.  This stuff needs to end up in the user manual
 though.

 It's a simple, easily-specified change.  I don't think we should hold it
 up because of a vague aspiration to implement fundeps in terms of type
 families; I'm sure there will be lots of ''other'' wrinkles to that.

 I would much prefer it done as a '''per-instance''' pragma, since we now
 have the technology to do that, rather than as a module-wide pragma.

 All it needs is for someone to do it.  I'm happy to advise.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8634#comment:64>
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