[GHC] #9951: OverloadedLists breaks exhaustiveness check

2 Jan 2015

      #9951: OverloadedLists breaks exhaustiveness check
-------------------------------------+-------------------------------------
              Reporter:  Feuerbach   |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.8.4
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
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 {{{#!hs
 {-# LANGUAGE OverloadedLists #-}

 module Bug where

 f :: [a] -> ()
 f x = case x of
   [] -> ()
   (_:_) -> ()
 }}}

 GHC reports:

 {{{
 bug.hs:6:7: Warning:
     Pattern match(es) are non-exhaustive
     In a case alternative: Patterns not matched: []
 }}}

 This is reproducible with 7.8 and 7.10rc1.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9951
GHC http://www.haskell.org/ghc/
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