shapeless-lenses.scala

    import shapeless._

    sealed trait Animal
    case class Point(x: Double, y: Double)
    case class Color(r: Byte, g: Byte, b: Byte)
    case class Turtle(position: Point, heading: Double, color: Color) extends Animal
    case class Cat(position: Point, color: Color) extends Animal

    implicit val turtlePosition = lens[Turtle].position
    implicit val catPosition = lens[Cat].position

    def updatePosition[T <: Animal](animal: T, pos: Point)(implicit ev: Lens[T, Point]) = ev.set(animal)(pos)

    updatePosition(t0, Point(0.0, 0.0))
    updatePosition(c0, Point(0.0, 0.0))