[GHC] #9701: GADTs not specialized properly

[GHC]

#9701: GADTs not specialized properly
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              Reporter:  dfeuer      |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.9
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:  Runtime     |       Blocked By:
  performance bug                    |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by dfeuer):

 I apologize for the terribly undiplomatic tone of my last message.
 Thinking over the matter some more, I believe that incoherent instances
 already interact about as badly as they can with GADTs. Specifically,
 consider what will happen when GADT values coming from two different
 modules and carrying incoherent instances come together—if I'm not
 mistaken, there's no way to predict which dictionary will be chosen for
 any given operation combining them.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9701#comment:6>
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