joohyung-park

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.

async/await is just the do-notation of the Promise monad

CertSimple just wrote a blog post arguing ES2017's async/await was the best thing to happen with JavaScript. I wholeheartedly agree.

In short, one of the (few?) good things about JavaScript used to be how well it handled asynchronous requests. This was mostly thanks to its Scheme-inherited implementation of functions and closures. That, though, was also one of its worst faults, because it led to the "callback hell", an seemingly unavoidable pattern that made highly asynchronous JS code almost unreadable. Many solutions attempted to solve that, but most failed. Promises almost did it, but failed too. Finally, async/await is here and, combined with Promises, it solves the problem for good. On this post, I'll explain why that is the case and trace a link between promises, async/await, the do-notation and monads.

First, let's illustrate the 3 styles by implementing

Technical overview

A basic `Option` type

// Option.ts

// definition
export class None {
  readonly tag: 'None' = 'None'

	import { Lens } from 'monocle-ts';
	import { id, prop, modify } from 'monocle-ts/Lens';
	import { pipe } from 'fp-ts/function';
	import { merge, set, cloneDeep } from 'lodash/fp';
	import produce from 'immer';

	interface Street {
	num: number;
	name: string;
	}

joohyung-park

Algebraic Effects in JavaScript part 1 - continuations and control transfer

async/await is just the do-notation of the Promise monad

Technical overview

A basic Option type

A basic `Option` type