[GHC] #10347: Spurious "unused constructor" warning with Coercible

[GHC]

#10347: Spurious "unused constructor" warning with Coercible
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        Reporter:  goldfire          |                   Owner:  goldfire
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.11
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by simonpj):

 In the example how could you ever construct a value of type `N a` (other
 than bottom)?

 You might add:
 {{{
 makeN :: Int -> N a
 makeN = N
 }}}
 and bingo you've used `N`.

 So actually the error message seems somewhat reasonable to me.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10347#comment:2>
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