Rough do notation decorator

do.py

import inspect


class Monad:
    def __init__(self, val):
        self.val = val

    def bind(self, func):
        return func(self.val)


def do(func):
    if not inspect.isgeneratorfunction(func):
        raise TypeError("not a generator")

    def wrapper(*args, **kwargs):
        loop = func(*args, **kwargs)

        def step(val):
            try:
                monad = loop.send(val)
            except StopIteration as stopper:
                return stopper.value
            else:
                return monad.bind(step)

        try:
            monad = next(loop)
        except StopIteration:
            raise RuntimeError("yield must be called at least once")
        else:
            return monad.bind(step)
    return wrapper


def get_first_name():
    return Monad("firstName")

def get_last_name():
    return Monad("lastName")

def get_full_name(first, last):
    return Monad(f"{first} {last}")


def get_name_nested():
    return get_first_name().bind(
        lambda first: get_last_name().bind(
            lambda last: get_full_name(first, last)
        )
    )

@do
def get_name():
    first = yield get_first_name()
    last = yield get_last_name()
    return get_full_name(first, last)

assert get_name_nested().val == get_name().val == "firstName lastName"