[GHC] #6093: Kind polymorphism fails with recursive type definition using different kind

[GHC]

#6093: Kind polymorphism fails with recursive type definition using different kind
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    Reporter:  Ashley Yakeley           |       Owner:                           
        Type:  bug                      |      Status:  new                      
    Priority:  normal                   |   Milestone:                           
   Component:  Compiler (Type checker)  |     Version:  7.4.1                    
    Keywords:                           |          Os:  Unknown/Multiple         
Architecture:  Unknown/Multiple         |     Failure:  GHC rejects valid program
  Difficulty:  Unknown                  |    Testcase:                           
   Blockedby:                           |    Blocking:                           
     Related:                           |  
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Comment(by sweirich):

 As Simon has elaborated, your example requires *kind* equalities (or
 GADKs) which aren't yet supported.  We're working on the theory that would
 allow us to add such kind equalities to FC now, but its not yet done (or
 implemented).

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6093#comment:5>
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