[GHC] #16315: Pattern synonym implicit existential quantification

[GHC]

#16315: Pattern synonym implicit existential quantification
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        Reporter:  int-index         |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
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 RyanGlScott):

 In case it wasn't clear:

 Replying to [comment:1 RyanGlScott]:
 > We also bring the "existential" (provided) type variables into scope so
 that if we find any occurrences of them in the pattern synonym body, //we
 can throw the relevant `APromotionErr` error//.

 (emphasis added)

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16315#comment:4>
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