Scala.jsFiddle gist

Main.scala

object ScalaJSExample extends js.JSApp{
  def pi(n: Int, tracer: ((Double, Double, Boolean) => Unit)) = {
    import scala.util.Random.nextDouble
    import scala.math.hypot
    def inQuadrant(a: Double, b: Double): Boolean = hypot(a,b)<=1.0
    def trySum(n: Int, m: Int): Double = n match {
        case 0 => m
        case _ => {
            val a = nextDouble
            val b = nextDouble
            val incircle = inQuadrant(a, b)
            tracer(a, b, incircle)
            trySum(n-1, m+{if(incircle) 1 else 0})
        }
    }
    4.0*trySum(n, 0).toDouble/n.toDouble
  }

  val (w, h) = (Page.canvas.height.toDouble, Page.canvas.height.toDouble)

  def pointTracer(a: Double, b: Double, inarea: Boolean) = {
    Page.renderer.fillStyle = if(inarea) "green" else "red"
    Page.renderer.fillRect(a*w, b*(h-25), 1, 1)
  }
  
  def main() = {
    var currentSum = 0.0;
    var currentN = 0;
    val step = 10;
    dom.setInterval(() => {
      currentSum += pi(step,pointTracer)
      currentN += 1
      Page.renderer.fillStyle = "black"
      Page.renderer.fillRect(0, h-20, w, 20)
      Page.renderer.fillStyle = "white"
      Page.renderer.fillText("Pi: " + (currentSum/currentN) toString , 10, h)
    }, 5)
  }
}

Monte Carlo method to calculate Pi digits with an on-line graphic representation of the sample.