maybe_python9.py

import functools


class MaybeException(Exception):
    pass


class Just:
    def __init__(self, value):
        self.value = value

    def __repr__(self):
        return f'Just {self.value}'


def maybe(fn):
    @functools.wraps(fn)
    def wrapper(*args, **kwargs):
        try:
            return Just(fn(*args, **kwargs))
        except Exception:
            return None
    return wrapper


@maybe
def divide(num, den):
    return num / den


@maybe
def positive_division(num, den):
    res = num / den
    if res <= 0:
        return None

    return res


def maybe_fn(default_val, fn, maybe_val):
    if maybe_val is None:
        return default_val

    return fn(maybe_val)


def is_just(maybe_val):
    return isinstance(maybe_val, Just)


def is_nothing(maybe_val):
    return maybe_val is None


def from_just(maybe_val):
    if not isinstance(maybe_val, Just):
        raise MaybeException('from_just: Nothing')

    return maybe_val.value


def from_maybe(default_val, maybe_val):
    if isinstance(maybe_val, Just):
        return maybe_val.value
    return default_val


def list_to_maybe(lst):
    return maybe(lambda x: x[0])(lst)


def maybe_to_list(maybe_val):
    if isinstance(maybe_val, Just):
        return [maybe_val.value]

    return []


def cat_maybes(maybes_lst):
    return [mv.value for mv in maybes_lst if isinstance(mv, Just)]


def map_maybe(map_maybe_fn, inp_lst):
    return [mv.value for mv in map(map_maybe_fn, inp_lst) if isinstance(mv, Just)]