factorial function in CPS

fac_cps.py

def bounce(func, *args):
    return ('bounce', func, args)


def land(value):
    return ('land', value)


def pogo(bouncer):
    ''' Keep bouncing until landing. '''
    while True:
        if bouncer[0] == 'land':
            return bouncer[1]
        else:  # 'bounce'
            bouncer = bouncer[1](*bouncer[2])

##########################################################################

#  1. trampolined style

def fac_t(n, k=1):
    return land(k) if n == 0 else bounce(fac_t, n - 1, k * n)

print pogo(fac_t(5))

#  2. continuation-passing style

def fac_k(n, k):
    return k(1) if n == 0 else\
           fac_k(n - 1, lambda f: k(n * f))

print fac_k(5, lambda n: n)

#  3. trampolined continuation-passing style

def fac_tk(n, k):
    return bounce(k, 1) if n == 0 else\
           bounce(fac_tk, n - 1, lambda f: bounce(k, n * f))

print pogo(fac_tk(5, lambda n: land(n)))