Stack-based implementation of the Ackermann function

stackermann.py

# https://www.sciencedirect.com/science/article/pii/0304397588900461

def stackermann(i, n):
	stack = []
	stack.append(i)
	stack.append(n)
	while len(stack) > 1:
		n = stack.pop()
		i = stack.pop()
		if i == 0:
			stack.append(n + 1)
		elif n == 0:
			stack.append(i - 1)
			stack.append(1)
		else:
			stack.append(i - 1)
			stack.append(i)
			stack.append(n - 1)
	return stack.pop()

n = 8
assert stackermann(0, n) == n + 1
assert stackermann(1, n) == n + 2
assert stackermann(2, n) == 2*n + 3
assert stackermann(3, n) == 2**(n+3) - 3