0 => int total;
fun int factorial(int i)
{
    if (i == 0) return 1;
    else
    {
        i * factorial(i - 1) => total;
    }
    return total;
}

// == another way
fun int factorial(int x)
{
    if (x <= 1 ) return 1;
    else return x * factorial (x - 1);
}

// call
factorial (5) => int answer;

// test
if ( answer == 120 ) <<<"success">>>;