example.py

example.py

class Option(object):
    def __init__(self, is_defined, value=None):
        self.is_defined = is_defined
        if is_defined:
            self.value = value

    @classmethod
    def Some(cls, value):
        return Option(True, value)

    @classmethod
    def _None(cls):
        return Option(False)

    # Functor Interface
    def map(self, func):
        if self.is_defined:
            return Option.Some(func(self.value))
        else:
            return Option._None()

    # Monad Interface
    @classmethod
    def _return(cls, value):
        return Option(True, value)

    def bind(self, func):
        if self.is_defined:
            return func(self.value)
        else:
            return Option._None()

class List(object):
    def __init__(self, values):
        self.values = values

    # Functor Interface
    def map(self, func):
        new_values = []
        for value in self.values:
            new_values.append(func(value))
        return List(new_values)

    # Monad Interface
    @classmethod
    def _return(cls, value):
        return List([value])

    def bind(self, func):
        new_values = []
        for value in self.values:
            new_values += func(value).values
        return List(new_values)

class Function(object):
    def __init__(self, func):
        self.func = func

    # Functor Interface
    def map(self, func):
        def new_func(value):
            return func(self.func(value))
        return Function(new_func)

    # Monad Interface
    @classmethod
    def _return(cls, value):
        def constant_func(ignore):
            return value
        return Function(constant_func)

    def bind(self, func):
        # This one is harder to write.