object Sum {

  def sum (f: Int => Int, a: Int, b: Int) = {
    def loop(a: Int, acc: Int): Int  =
      if (a > b) acc
      else loop(a + 1, f(a) + acc)
    loop(a, 0)
  }

  def run =
    println(sum(x => x * x, 3, 5))

}