[GHC] #11067: Spurious superclass cycle error with type equalities

[GHC]

#11067: Spurious superclass cycle error with type equalities
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        Reporter:  oerjan            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by oerjan):

 András Kovács
 [https://github.com/ekmett/constraints/issues/11#issuecomment-154726144
 found a workaround] for our use case: The error disappears if `Forall`
 etc. are made type synonym families rather than plain synonyms.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11067#comment:2>
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