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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

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	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Jumping Game</title>
	<style>
	canvas {
	border: 1px solid black;
	}

	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<title>Jumping Game</title>
	<style>
	canvas {
	border: 1px solid black;
	}

	import Foundation
	import SwiftUI
	import UIKit

	extension UIBlurEffect {
	public static func variableBlurEffect(radius: Double, imageMask: UIImage) -> UIBlurEffect? {
	let methodType = (@convention(c) (AnyClass, Selector, Double, UIImage) -> UIBlurEffect).self
	let selectorName = ["imageMask:", "effectWithVariableBlurRadius:"].reversed().joined()
	let selector = NSSelectorFromString(selectorName)

	#!/bin/bash
	# java shim to execute anything java within a distroless, rootless container
	# designed for podman 4, breaks with podman 3 because of different --pull syntax
	# https://iptables.sh

	set -euo pipefail

	IMAGE="gcr.io/distroless/java21:nonroot"

	# check for podman

	param(
	[switch]$verbose
	)

	# The variables starting with $GLOBAL store values that should be applied to all XHCI controllers by default.
	# To override this default value on a per-controller basis, specify the DEV_XXXX hardware ID value for the XHCI controller along with its data
	# See the example below.
	#
	# $globalInterval = 0x0
	# $globalHCSPARAMSOffset = 0x4

	import sys
	from time import sleep
	from selenium import webdriver
	from selenium.common.exceptions import TimeoutException
	from selenium.common.exceptions import WebDriverException
	from eliot import start_action, to_file, log_call
	# from selenium.webdriver.common.keys import Keys
	# from selenium.webdriver.common.desired_capabilities import DesiredCapabilities
	# from selenium.webdriver.common.by import By
	# from selenium.webdriver.support import expected_conditions as EC