[GHC] #9951: OverloadedLists breaks exhaustiveness check

[GHC]

#9951: OverloadedLists breaks exhaustiveness check
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        Reporter:  Feuerbach         |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.8.4
      Resolution:                    |                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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Comment (by Feuerbach):

 Thanks Martin, that desugaring explains everything. I didn't know it was
 so simple.

 The cause of the difference you point is that the cons pattern, `_:_`, is
 not overloaded.

 The question then becomes, should there be some way to write the non-
 overloaded empty list constructor even when OverloadedLists is on?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9951#comment:2>
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