[GHC] #13578: Incorrect Record Pattern Synonym example in users guide

14 Apr 2017

      #13578: Incorrect Record Pattern Synonym example in users guide
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           Reporter:  cjholdbrooks   |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Documentation  |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Documentation
  Unknown/Multiple                   |  bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 The first example in section 9.7.1 of the users guide provides the example

 {{{#!hs
 pattern Point :: (Int, Int)
 pattern Point{x, y} = (x, y)
 }}}

 which results in the error

 {{{
    • Pattern synonym ‘Point’ has two arguments
        but its type signature has none
    • In the declaration for pattern synonym ‘Point’
 }}}

 upon load.

 I believe the correct code is as follows.

 {{{#!hs
 pattern Point :: Int -> Int -> (Int, Int)
 pattern Point{x, y} = (x, y)
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13578
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