append cps

def identity(x):
    return x

def append(l1, l2):
    def append_cps(l1, l2, k):
        if not l1:
            return k(l2)

        def arrange(appended):
            return k([l1[0]] + appended)

        return append_cps(l1[1:], l2, arrange)

    return append_cps(l1, l2, identity)