[GHC] #10532: Unnecessary constraints when using overlapping instances

[GHC]

#10532: Unnecessary constraints when using overlapping instances
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        Reporter:  MikeIzbicki       |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler (Type    |                 Version:  7.10.1
  checker)                           |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by MikeIzbicki):

 I don't understand why this would be expected behavior.  GHC lets me
 remove the constraint when overlapping instances are not involved, but
 requires the constraint when overlapping instances are involved.  Why
 should there be a difference when overlapping instances gets involved?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10532#comment:3>
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