simple stack-based computations

stack_computations.py

# stack_computations.py
"""
 Simple example stack computations
"""


"""
    Stack diagram
        f(n)
        f(n-1)
        ..
        ..

stack computation: push f(n), push f(n-1),.., 1, ... pop f(n-1), pop f(n)
"""

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

def stack_f(n):
    stack = []
    while n >= 1:
        stack.append(n)
        n -= 1
    returnv = 1
    # in this case the stack item calculation is
    # to multiply the current int value times the returned value
    # of the previous stack calculation
    while stack:
        m = stack.pop()
        returnv = returnv * m
    return returnv

for i in range(1, 10):
    print(f'factorial of {i}: {f(i)} stack result: {stack_f(i)}')

"""

call dependency tree

    main
    /  \
  h(3)  g(4)

push main, push h(3), pop h(3), push g(4), pop g(4), pop main
"""

def main():
    a = 3
    b = 4
    return h(a) * g(b)

def stack_main():
    stack = list()
    stack.append(main)
    stack.append((h, 3))
    func, val = stack.pop()
    res1 = func(val)
    stack.append((g, 4))
    func2, val2 = stack.pop()
    res2 = func2(val2)
    res = res1 * res2
    return res

def g(n):
    return n**2

def h(n):
    return n + 3

print(f"\nmain(): {main()} stack_main(): {stack_main()}")