'''lecture_34_sum_list.py
Use recursion to sum a list
Oliver W. Layton
CS 151: Computational Thinking: Visual Media
Fall 2020
'''


def sum(list):
    if len(list) == 1:  # base case
        return list[0]
    else:
        # first item + sum of the rest
        return list[0] + sum(list[1:])


if __name__ == '__main__':
    # print(sum([1, 4, 3]))
    # print(sum([4, 1, 95, 100]))
    # print(sum([4]))  # one function symbol table
    # print(sum([4, 1]))  # two function symbol tables
    print(sum([4, 1, 3]))  # three function symbol tables (see below)

    # 1st call: list = [4, 1, 3], list[0] = 4, list[1:] = [1, 3]
    # 2nd call: list = [1, 3], list[0] = 1, list[1:] = [3]
    # 3rd call: list = [3], list[0] = 3, -> we hit return list[0] and backtrack