node ordering

ordering.scala

sealed trait Node[T]
case class Leaf[T](v: T) extends Node[T]
case class Branch[T](l: Node[T], r: Node[T]) extends Node[T]

implicit def nodeOrdering[W, C](implicit num: Numeric[W]): Ordering[Node[(W, C)]] = {
  def weight(a: Node[(W, C)]): Tuple2[W, C] = a match {
    case Leaf((w, c)) => (w, c)
    case Branch(l, r) => {
      val (wl, cl) = weight(l)
      val (wr, _) = weight(r)
      (num.plus(wl, wr), cl)
    }
  }
  Ordering.by(weight)
  // No implicit Ordering defined for (W, C).
  // not enough arguments for method by: (implicit ord: scala.math.Ordering[(W, C)])scala.math.Ordering[Node[(W, C)]]. Unspecified value parameter ord.
}

implicit def nodeOrdering[W: Ordering, C: Ordering](implicit num: Numeric[W]): Ordering[Node[(W, C)]]