Scala program to calculate factorial of a number

Factorial.scala

// $ sbt
// sbt:factorial> ~run 10
// [info] running sample.Sample 10
// 3628800
package sample

object Sample extends App {
  println(factorial(args(0).toLong).toString)

  def factorial (num: Long) : Long = {
    if (num == 0) {
      return 1
    }
    return num * factorial(num - 1)
  }
}