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Algebraic Effects in JavaScript part 4 - Implementing Algebraic Effects and Handlers

This is the final part of a series about Algebraic Effects and Handlers.

So we've come to the core topic. The reality is that we've already covered most of it in the previous parts. Especially, in the third part, where we saw delimited continuations at work.


Algebraic Effects in JavaScript part 2 - Capturing continuations with Generators

This is the second part of a series about Algebraic Effects and Handlers.

Note: initially I planned a 3-part series, but since the current post on undelimited continuations ended up taking

View multishot-callcc.js
function isGenerator(x) {
return x != null && typeof === "function"
function isFrame(x) {
return x != null && x._type_ === 'call_frame'
function call(genFunc, ...args) {

Algebraic Effects in JavaScript part 1 - continuations and control transfer

This is the first post of a series about Algebraic Effects and Handlers.

There are 2 ways to approach this topic:

  • Denotational: explain Algebraic Effects in terms of their meaning in mathematics/Category theory
  • Operational: explain the mechanic of Algebraic Effects by showing how they operate under a chosen runtime environment

Both approaches are valuables and give different insights on the topic. However, not everyone (including me), has the prerequisites to grasp the concepts of Category theory and Abstract Algebra. On the other hand, the operational approach is accessible to a much wider audience of programmers even if it doesn't provide the full picture.

View delimited-continuations.js
// We model the call stack using a linked list of Generators
// Each Generator has a _return field pointing back to its parent
function stepGen(gen, arg) {
const {done, value} =
if(done) {
if(gen._return) {
stepGen(gen._return, value)
View abort.js
function*example() {
const x = 10
const y = yield callcc(function*(k) {
// ...
yield k(20)
throw "Unreachable code"
console.log(x + y)

In this tutorial we're going to build a set of parser combinators.

What is a parser combinator?

We'll answer the above question in 2 steps

  1. what is a parser?
  2. and.. what is a parser combinator?

So first question: What is parser?

View App.js
import React from 'react';
import reclass from './reclass';
import Greeter from './Greeter';
function App(ctx) {
ctx.state = { civility: 'Mr.' };
function changeCivility(e) {
ctx.setState({ civility: });
View SimpleSagaMiddleware.html
<!doctype html>
<html lang="en">
const sagaMiddleware = store => gen => {
var resolve, reject
var done = new Promise((res, rej) => {
resolve = res