Monads: Simple made Easy.

monads.py

from functools import reduce


class Maybe(object):
    def __str__(self):
        return "Maybe"


class Something(Maybe):
    def __init__(self, value):
        self.value = value

    def __str__(self):
        return f"Something {self.value}"


class Nothing(Maybe):
    def __str__(self):
        return "Nothing"


def read_and_add(prev):
    try:
        n = int(input("Enter a number: "))

        return Something(prev + n)
    except Exception:
        return Nothing()


def bind(m, f):
    if isinstance(m, Something):
        return f(m.value)
    else:
        return Nothing()


def unit(value):
    return Something(value)


def chain(value, *functions):
    return reduce(bind, functions, value)


def sum_of_3_nums():
    return chain(
        unit(0),
        read_and_add,
        read_and_add,
        read_and_add
    )


if __name__ == '__main__':
    r = sum_of_3_nums()

    print(r)