[GHC] #13778: explicitly bidirectional patterns should not report Recursive definition" when used in view pattern expression position

2 Jun 2017

      #13778: explicitly bidirectional patterns should not report Recursive definition"
when used in view pattern expression position
-------------------------------------+-------------------------------------
           Reporter:  heisenbug      |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.3
           Keywords:                 |  Operating System:  Unknown/Multiple
  PatternSynonyms                    |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Compile this

 {{{#!hs
 pattern One <- ((==One) -> True)
   where One = 1
 }}}

 I get

 {{{
 test.hs:1:1: error:
     Recursive pattern synonym definition with following bindings:
       One (defined at test.hs:(1,1)-(1,15))
   |
 Compilation failed.
 }}}

 Note that the error is due to the usage in view pattern **expression
 position**.

 But for ''explicitly bidirectional'' patterns, there is no recursivity
 going on. So this usage should be allowed.

 I am testing with HEAD, but the issue is probably older.

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13778
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