[GHC] #14822: -XQuantifiedConstraints: Turn term-level entailments (:-) into constraints (=>)

[GHC]

#14822: -XQuantifiedConstraints: Turn term-level entailments (:-) into constraints
(=>)
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        Reporter:  Iceland_jack      |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.5
      Resolution:  invalid           |             Keywords:
                                     |  QuantifiedConstraints, wipT2893
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Iceland_jack):

 Using #14292 this can be `coerce`d rather than `unsafeCoerce`d if only we
 turn on `-XIncoherentInstances` and mark some parameters
 `representational`

 {{{#!hs
 type role Implies nominal representational
 type role Str representational
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14822#comment:4>
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