Simple illustration of recursion as it is sometimes used in functional languages

functional.py

# Again, these are contrived examples, but they do a slightly better job of
# illustrating the use of recursion in functional languages when no concept of
# program state is available.


# Notice that the if statement in the functional example 1 includes an else
# statement.  This makes it more like a mathematical expression (because it
# causes the function to always return a certain value).  Functional example 2
# uses a syntax available in python that truly is an expression built with if
# and else statements.


def add_imperative(n):
    """
    Adds one to a total `n` times in the style of an imperative language.
    """
    total = 0
    for i in range(n):
        total += 1
    return total


def add_functional_1(n):
    """
    Adds one to a total `n` times in the style of a functional language.
    """
    if n == 0:
        return 0
    else:
        return 1 + add_functional_1(n - 1)


def add_functional_2(n):
    """
    Adds one to a total `n` times in the style of a functional language.
    """
    return 0 if n == 0 else 1 + add_functional_2(n - 1)