factorial

factorial-nontailrecursion.scala

object factorialTest extends App
{
    def factorial(n: Int): Int =
    {
        if(n == 0) 1 else n * factorial(n-1)
    }


    println(factorial(3))
    println(factorial(10))
}

factorial-tailrecursion.scala

object factorialTest extends App
{
    def factorialRecur(n: Int, acc: Int): Int =
    {
        if(n == 0) acc else factorialRecur(n-1, acc*n)
    }

    def factorial(n: Int) = factorialRecur(n, 1)

    println(factorial(3))
    println(factorial(10))
}

To transform a non-tail recursion to tail recursion, just use a parameter to hold and accumulate the results.