[GHC] #12166: Pattern synonym existential variable confusion

[GHC]

#12166: Pattern synonym existential variable confusion
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        Reporter:  goldfire          |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:  invalid           |             Keywords:
                                     |  PatternSynonyms
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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Changes (by goldfire):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 Perhaps you're right. The big difference between your examples and mine is
 that yours indeed bring some existential into scope. Your pattern
 signature restricts the usefulness of these existentials. In my example,
 though, there is no existential at all brought into scope in the pattern,
 even though there is in the signature.

 That said, my case is contrived (and I think all examples like mine would
 be) and there's no lint error, so I'll stand down.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12166#comment:2>
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