[GHC] #10335: Failure to construct superclasses in instance

[GHC]

#10335: Failure to construct superclasses in instance
-------------------------------------+-------------------------------------
        Reporter:  simonpj           |                   Owner:
            Type:  bug               |                  Status:  merge
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |  typecheck/should_compile/T10335
                                     |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
Changes (by simonpj):

 * status:  new => merge
 * testcase:   => typecheck/should_compile/T10335


Comment:

 Fixed, although the patch probably won't apply very nicely to 7.10.2,
 because it meddles with `TcEvidence` which has changed since 7.10.

 But this patch effectively reverts one of the changes to `TcEvidence` so
 while it won't apply automatically, it won't be hard either.  I'm inclined
 to think it's worth merging.  I can help.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10335#comment:2>
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