[GHC] #8710: Overlapping patterns warning misplaced

[GHC]

#8710: Overlapping patterns warning misplaced
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       Reporter:         |             Owner:
  goldfire               |            Status:  new
           Type:  bug    |         Milestone:
       Priority:  low    |           Version:  7.7
      Component:         |  Operating System:  Unknown/Multiple
  Compiler               |   Type of failure:  Incorrect warning at
       Keywords:         |  compile-time
   Architecture:         |         Test Case:
  Unknown/Multiple       |          Blocking:
     Difficulty:         |
  Unknown                |
     Blocked By:         |
Related Tickets:         |
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 Consider

 {{{
 {-# OPTIONS_GHC -fwarn-overlapping-patterns #-}

 len []    = 0
 len (_:t) = 1 + len t
 len _     = error "urk"
 }}}

 GHC reports the problem with this definition at the first line of it. I
 think it would be more helpful to have it at the last line, which is the
 pattern that will never match.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8710>
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