[GHC] #11466: Constraint synonym with Implicit Parameter

[GHC]

#11466: Constraint synonym with Implicit Parameter
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        Reporter:  nomeata           |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  polykinds/T11466
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 {{{
 instance ?x::Int => Eq T
 }}}
 No it should not be allowed!  Instances are resolved in unpredicatable
 places, which is incompatible with knowing exactly which `?x` is used.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11466#comment:11>
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