[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):

 Regarding syntax, could it use data constructor syntax with a magic module

 {{{#!hs
 import GHC.OrPatterns ( (:|:) ) -- ( pattern (:|:) ) ?

 f A = ...
 f B = ...
 f unexpected@(C{} :|: D{} :|: E{}) = pprTrace "f" (ppr unexpected)
 }}}

 like Edward's suggestion in
 Records/OverloadedRecordFields/OverloadedLabels

 {{{#!hs
 import GHC.ImplicitValues( p, q, area )
 }}}

 ----

 {{{#!hs
 import qualified GHC.OrPatterns as OR ( (:|:) )

 f (C{} OR.:|: D{} OR.:|: E{}) = ...
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3919#comment:15>
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