[GHC] #8581: Pattern synonym used in an expression context could have different constraints to pattern used in a pattern context

[GHC]

#8581: Pattern synonym used in an expression context could have different
constraints to pattern used in a pattern context
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        Reporter:  cactus            |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:
      Resolution:                    |             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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Comment (by dfeuer):

 Replying to [comment:38 goldfire]:
 > A. None at all.

 I'm very much in favor of A. See also #11646.

 > Now, onto design point (2). I wonder if it's helpful to think of pattern
 synonym types as a `(PatternType, Maybe Type)`.

 I think what we actually want (borrowing from the
 [https://hackage.haskell.org/package/these these] package) is `These
 PatternType Type`. That is, either just the pattern, just the constructor,
 or both.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8581#comment:39>
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