[GHC] #13300: panic! isInjectiveTyCon sees a TcTyCon W

[GHC]

#13300: panic! isInjectiveTyCon sees a TcTyCon W
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        Reporter:  siddhanathan      |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 For those like me who failed to spot the error immediately, the correct
 error message is (from 7.10)
 {{{
 W.hs:4:3:
     Data constructor ‘WI’ returns type ‘Int’
       instead of an instance of its parent type ‘W’
     In the definition of data constructor ‘WI’
     In the data declaration for ‘W’
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13300#comment:1>
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