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trait Box[ K[A[x]] ]
object Box {
// type constructor composition
sealed trait ∙[A[_], B[_]] { type l[T] = A[B[T]] }
// composes type constructors inside K
type SplitBox[K[A[x]], B[x]] = Box[ ({ type l[A[x]] = K[ (A ∙ B)#l] })#l ]
def split[ K[A[x]], B[x] ](base: Box[K]): SplitBox[K,B] = ???
class Composed[B[_], K[A[x]] ] {
val box: Box[K] = ???
type Split[ A[x] ] = K[ (A ∙ B)#l ]
val a: Box[Split] = Box.split(box)
//Either of these work:
//val a: Box[Split] = Box.split[K,B](box)
//val a: Box[ ({ type l[A[x]] = K[ (A ∙ B)#l ] })#l ] = Box.split(box)
}
}
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