Defining implicit view-bounds on Scala traits

Question

I\'m doing an exercise to implement a functional binary-search-tree in Scala, following a similar pattern that I\'ve seen used in Haskell. I have a structure that looks somethin

Answer 1

You could provide the "evidence" that A is Ordered by requiring an abstract member of type Ordered[A] on the trait:

trait TreeNode[A] {
  implicit val evidence: Ordered[A]
}

You would then be forced to provide this in any concrete subtypes, this proving that A is Ordered:

case class Leaf[A](value: A)(implicit ev: Ordered[A]) extends TreeNode[A] {
  val evidence = ev
}

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You might instead want to constrain A to a type which has an implicit Ordering[A] - this is not an inheritance relationship; it is more like a haskell typeclass. But the implementation in terms of the above technique would be the same.