[GHC] #15893: View Patterns affect typechecking in an unpredictable manner

[GHC]

#15893: View Patterns affect typechecking in an unpredictable manner
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        Reporter:  theindigamer      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  ⊥
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:  ViewPatterns
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Wow.  Here's an example with no dependencies
 {{{
 bar :: Int -> (Int,Int)
 bar i = (t_pre, t_post)
   where
     f :: Int -> Int
     f j = j
     (f -> t_pre, f -> t_post) = (i+1, i-1)
 }}}
 We get
 {{{
 T15893.hs:10:6: error:
     * Variable not in scope: f :: Int -> t
     * Perhaps you meant `f' (line 9)
    |
 10 |     (f -> t_pre, f -> t_post) = (i+1, i-1)
    |      ^
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15893#comment:1>
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