[GHC] #15290: QuantifiedConstraints: panic "addTcEvBind NoEvBindsVar"

[GHC]

#15290: QuantifiedConstraints: panic "addTcEvBind NoEvBindsVar"
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
                                     |  QuantifiedConstraints
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:  9123, 14883
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 > Wait, you're saying that deriving classes with methods that use higher-
 rank types will no longer work?

 No, I am not saying that (see the second bullet).  It's just that if you
 can't ''simultaneously'' exploit impredicative instantiation of `coerce`
 and quantified constraints.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15290#comment:9>
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