Contravariant[Ordering]

OrderingContravariantExample.scala

import scalaz._
import scala.math.Ordering

implicit val orderingContra: Contravariant[Ordering] = new Contravariant[Ordering] {
  def contramap[A, B](r: Ordering[A])(f: B => A): Ordering[B] = r.on(f)
}

case class Doodad(description: String, priceCents: Int)

import scalaz.syntax.contravariant._

implicit val doodadOrdering = Ordering[Int].contramap[Doodad](_.priceCents)

// prints List(Doodad(y,75), Doodad(x,125))
println(List(Doodad("x", 125), Doodad("y", 75)).sorted)