BigIntFactorial.scala

/**
  * Created by spectrum on Jun, 2018
  */
object BigIntFactorial {
  implicit def enhanceBigInt(n: BigInt) = new {
    private val One = BigInt(1)
    def ! = (One /: (One to n)) (_ * _)
  }

  val Zero = BigInt(0)
  def factorial(n: BigInt): BigInt = n match {
    case Zero => 1
    case x: BigInt => x * factorial(x - 1)
  }

  def main(args: Array[String]): Unit = {
    println(BigInt(4)!)
    println(factorial(BigInt(10)))
  }
}