[GHC] #3919: Or-patterns as GHC extension

[GHC]

#3919: Or-patterns as GHC extension
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        Reporter:  BjornEdstrom      |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  ⊥
       Component:  Compiler          |              Version:
      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 Iceland_jack):

 What about where `|` starts a guard? This parses just fine

 {{{#!hs
 f = \case
   True | False -> ...
 }}}

 One option is to mandate parentheses in that case (`(True | False) ->
 ...`) or to use some messier syntax `:|`, `:|:` ... I don't think or-
 patterns are common enough that will matter greatly.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3919#comment:17>
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