[GHC] #5691: Crash: strange interaction of ScopedTypeVariables extension with type class name resolution

[GHC]

#5691: Crash: strange interaction of ScopedTypeVariables extension with type class
name resolution
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 Reporter:  dominiquedevriese   |          Owner:                                   
     Type:  bug                 |         Status:  new                              
 Priority:  normal              |      Component:  Compiler (Type checker)          
  Version:  7.0.4               |       Keywords:  ScopedTypeVariables, type classes
       Os:  Unknown/Multiple    |   Architecture:  Unknown/Multiple                 
  Failure:  Compile-time crash  |       Testcase:                                   
Blockedby:                      |       Blocking:                                   
  Related:                      |  
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Comment(by dominiquedevriese):

 Oh, I forgot to say: the problem seems to be that GHC doesn't notice that
 there is no instance for Monad RecDecParser when I define the instance
 MonadPlus RecDecParser. The problem strangely disappears if I remove the
 type annotation on f in the Test instance for unrelated PrintRuleInterp.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5691#comment:1>
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