[GHC] #5144: Pattern synonyms

[GHC]

#5144: Pattern synonyms
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        Reporter:  simonpj           |            Owner:  cactus
            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      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by cactus):

 I've implemented infix notation as well, so now you can write this:

 {{{
 {-# LANGUAGE ViewPatterns, PatternSynonyms #-}
 import qualified Data.Sequence as Seq

 pattern Empty = (Seq.viewl -> Seq.EmptyL)
 pattern x :< xs = (Seq.viewl -> x Seq.:< xs)
 pattern xs :> x = (Seq.viewr -> xs Seq.:> x)

 zipZag :: Seq.Seq a -> Seq.Seq b -> Seq.Seq (a, b)
 zipZag (x :< xs) (ys :> y) = (x, y) Seq.<| zipZag xs ys
 zipZag _         _         = Seq.empty
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5144#comment:18>
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