[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 simonmar):

 We need to think about the import/export situation.  One of the goals of
 pattern synonyms is to abstract constructors, so that a library can change
 a data type representation while allowing clients to continue to use
 pattern matching.  Clearly we can't use the `T(P1,P2,..)` syntax for
 exporting patterns (what is `T`?), but perhaps we can use the `pattern`
 syntax for exporting constructors.  I haven't thought about this very
 hard.

 When a pattern is imported, can it be used in an expression?  Does the
 client know whether it can be used in an expression or not?

 What do the Haddock docs for pattern synonyms look like?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5144#comment:21>
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