[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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Changes (by simonpj):

 * cc: goldfire, dreixel (added)


Comment:

 Hmm. So you want to get the following type and kind signatures (where I
 put in all kind abstractions and applications):
 {{{
   Type :: forall k. k -> *
   SimpleType :: forall (a:*). IOWitness a -> Type * a
   ConstructedType :: forall k k2. forall (f:k2->k) (a:k2).
                      Type (k2->k) g -> Type k2 a -> Type k (f a)
 }}}
 But there's a difficulty with `SimpleType` because data constructors must
 have competely parameteric result types.  I think you really want
 {{{
   SimpleType :: forall k. (k ~ *) => forall (a:k). IOWitness a -> Type k a
 }}}
 I'm a bit out of my depth here, but Stephanie and Richard have been
 working on this kind of stuff so I'm ccing them.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6093#comment:4>
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