object Sqrt {

  def abs(x:Double) = if (x < 0) -x else x

  def sqrt(x: Double) = {

    def sqrtIter(guess: Double): Double =
      if (isGoodEnough(guess)) guess
      else sqrtIter(improve(guess))

    def isGoodEnough(guess: Double) =
      abs(guess * guess - x ) /x < 0.001

    def improve(guess: Double) =
      (guess + x / guess) / 2

    sqrtIter(1.0)
  }

  def run =
    println(sqrt(2))
    println(sqrt(0.001))
    println(sqrt(0.1e-20))
    println(sqrt(1.0e20))
    println(sqrt(1.0e50))

}