[GHC] #2356: GHC accepts multiple instances for the same type in different modules

[GHC]

#2356: GHC accepts multiple instances for the same type in different modules
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    Reporter:  claus     |        Owner:         
        Type:  bug       |       Status:  new    
    Priority:  normal    |    Milestone:         
   Component:  Compiler  |      Version:  6.8.2  
    Severity:  normal    |   Resolution:         
    Keywords:            |     Testcase:         
Architecture:  Unknown   |           Os:  Unknown
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Changes (by guest):

 * cc: lennart at augustsson.net (added)

Comment:

 This really surprises me.  Why doesn't think produce a link error?
 Each instance declaration should give rise to a global symbol uniquely
 determined by the class and the type, I'd presume.  And when they meet
 there will be a clash.
 Obviously I'm wrong, as this (scary) example shows.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2356#comment:1>
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