Simple demo of algebraic effects in Python. This doesn't show the full potential; it's just a proof-of-concept

algebraic_effects.py

import sys

class Effect:
    def __enter__(self):
        self.local_handlers = sys._getframe().f_back.f_locals.setdefault("_effect_handlers", [])
        self.local_handlers.append(self)

    def __exit__(self, *args):
        self.local_handlers.pop()

    def __call__(self, key, *args, **kwargs):
        if hasattr(self, f"handle_{key}"):
            return getattr(self, f"handle_{key}")(*args, **kwargs)
        elif hasattr(self, "handle"):
            return getattr(self, "handle")(*args, **kwargs)
        return NotImplemented


class Printer(Effect):
    def __init__(self, prefix):
        self.prefix = prefix

    def handle_print(self, val):
        print(self.prefix, val)


def perform(value, *args, **kwargs):
    frame = sys._getframe()
    handled = False
    while frame := frame.f_back:
        if "_effect_handlers" in frame.f_locals:
            for handler in reversed(frame.f_locals["_effect_handlers"]):
                if (retval := handler(value, *args, **kwargs)) is not NotImplemented:
                    return retval
    raise RuntimeError("unhandled effect")


def something():
    perform("print", "hello")

with Printer("outer"):
    something()
    with Printer("inner"):
        something()
    something()