maybe monad in python

maybe.py

"""
Maybe monad in Python

use `Just(x)` instead of `return x`
"""

class Maybe():
    def __and__(self, k): # a >>= b
        if self.__class__ == __Nothing:
            return Nothing
        elif self.__class__ == Just:
            return k(self.dim)
    def __rshift__(self, k):
        return self & (lambda _: k)

class _Maybe__Nothing(Maybe):
    def __repr__(self):
        return "Nothing"

Nothing = _Maybe__Nothing()

class Just(Maybe):
    def __init__(self, x):
        self.dim = x
    def __repr__(self):
        return "Just(%r)" % self.dim