object Planet extends Enumeration {

  // universal gravitational constant (m3 kg-1 s-2)
  val G = 6.67300E-11

  val Mercury = Planet(3.303e+23, 2.4397e6)
  val Venus = Planet(4.869e+24, 6.0518e6)
  val Earth = Planet(5.976e+24, 6.37814e6)
  val Mars = Planet(6.421e+23, 3.3972e6)
  val Jupiter = Planet(1.9e+27, 7.1492e7)
  val Saturn = Planet(5.688e+26, 6.0268e7)
  val Uranus = Planet(8.686e+25, 2.5559e7)
  val Neptune = Planet(1.024e+26, 2.4746e7)

  case class Planet(mass: Double, radius: Double) extends Val {

    def surfaceGravity: Double = G * mass / (radius * radius)

    def surfaceWeight(otherMass: Double) = otherMass * surfaceGravity

  }

}

object PlayEnumeration extends App {


  val earthWeight = 175
  val mass = earthWeight / Planet.Earth.surfaceGravity

  Planet.values.foreach {
    // Does not compile as might be expected.
    // value surfaceWeight is not a member of play.Planet.Value
    p => println(s"Your weight on $p is ${p.surfaceWeight(mass)}")
  }

  println

}

scala> implicit def `plutoid`(p: Planets.Value): Planets.Planet = p.asInstanceOf[Planets.Planet]
warning: there were 1 feature warning(s); re-run with -feature for details
plutoid: (p: Planets.Value)Planets.Planet

scala> for (p <- Planets.values) Console println s"Your weight on $p is ${p.surfaceWeight(mass)}"
[snip]