[GHC] #6118: Kind variable falls out of scope in instance declaration

[GHC]

#6118: Kind variable falls out of scope in instance declaration
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  Reporter:  goldfire          |          Owner:                  
      Type:  bug               |         Status:  closed          
  Priority:  normal            |      Milestone:                  
 Component:  Compiler          |        Version:  7.5             
Resolution:  fixed             |       Keywords:  PolyKinds       
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown      |     Difficulty:  Unknown         
  Testcase:  polykinds/T6118   |      Blockedby:                  
  Blocking:                    |        Related:                  
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Changes (by simonpj):

  * status:  new => closed
  * testcase:  => polykinds/T6118
  * resolution:  => fixed


Comment:

 OK I've fixed the bug. But I did have to add `-XUndecidableInstances` to
 make the type instances go through.  Less conservative termination tests
 welcomed. Anything involving kind polymorphism is going to involve
 multiple occurrences of the kind variable on the RHS.  The kind is seldom
 the index; but it can be.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6118#comment:3>
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