cps.py

def fact(n):
    if n == 0:
        return 1
    else:
        return n * fact(n - 1)

def fact_cps(n, k=lambda x: x):
    if n == 0:
        return k(1)
    else:
        return fact_cps(n-1, lambda x: k(n * x))


def fact_loop(n, k=lambda x: x):
    def factory(n, k):
        return lambda x: k(n * x)
    while True:
        if n == 0:
            return k(1)
        else:
            k = factory(n, k)
            n -= 1

def fact_with_stack(n, k=()):
    while True:
        if n == 0:
            x = 1
            while k:
                x = k[0] * x
                k = k[1]
            return x
        else:
            k = (n, k)
            n -= 1