[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):

 If your question is whether there's a syntactic way to see if a given
 pattern synonym import can be used as an expression, then no, not at the
 moment. So if you do something like

 {{{
 import M(pattern P)

 x = P
 }}}

 then the only error you will get if `P` is not bidirectional is from the
 type checker:

 {{{
 /tmp/hs/M2.hs:5:5:
     P used in an expression, but it's a non-bidirectional pattern synonym
     In the expression: P
     In an equation for ‛x’: x = P
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5144#comment:22>
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