Rich richdouglasevans

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

Using `<details>` in GitHub

Suppose you're opening an issue and there's a lot noisey logs that may be useful.

Rather than wrecking readability, wrap it in a <details> tag!

<details>
 Summary Goes Here

	const { Left, Right } = require('fantasy-eithers')
	const daggy = require('daggy')

	Function.prototype.map = function (f) {
	return x => f(this(x))
	}

	//- Where everything changes...
	const login = user =>
	user.name == 'Tom'

	const { tagged } = require('daggy')

	const First = tagged('val')

	First.prototype.concat = function (that) {
	return this
	}

	const Min = tagged('val')

	quicksort :: (Ord a) => [a] -> [a]
	quicksort [] = []
	quicksort (x:xs) =
	let smallerSorted = quicksort (filter (<=x) xs)
	biggerSorted = quicksort (filter (>x) xs)
	in smallerSorted ++ [x] ++ biggerSorted

	ssh-keygen -t rsa -b 4096 -m PEM -f jwtRS256.key
	# Don't add passphrase
	openssl rsa -in jwtRS256.key -pubout -outform PEM -out jwtRS256.key.pub
	cat jwtRS256.key
	cat jwtRS256.key.pub

	FROM debian

	RUN apt-get update && apt-get install -y curl

	RUN curl https://raw.githubusercontent.com/LuRsT/hr/master/hr > /bin/hr
	RUN chmod +x /bin/hr

	# Requires:
	# a) `jq` to be installed
	# b) A Bearer token (you can grab this from the healthgraph debug console)


	export BEARER=MY_TOKEN_FROM_THE_CONSOLE

	curl https://api.runkeeper.com/fitnessActivities?pageSize=100 -H "Authorization: Bearer $BEARER" > page1.json
	curl https://api.runkeeper.com/fitnessActivities?pageSize=100&page=2 -H "Authorization: Bearer $BEARER" > page2.json
	curl https://api.runkeeper.com/fitnessActivities?pageSize=100&page=3 -H "Authorization: Bearer $BEARER" > page3.json

	$EC2SettingsFile="C:\\Program Files\\Amazon\\Ec2ConfigService\\Settings\\BundleConfig.xml"
	$xml = [xml](get-content $EC2SettingsFile)
	$xmlElement = $xml.get_DocumentElement()

	foreach ($element in $xmlElement.Property)
	{
	if ($element.Name -eq "AutoSysprep")
	{
	$element.Value="Yes"
	}

	<html>
	<head>
	<script type="text/javascript">

	var baseUrl = 'http://netrunnerdb.com/en/card/';
	var maxSetId = 8;
	var cardsCoreSet = 119;
	var cardsBigBox = 55;
	var cardsCycle = 120;

Rich richdouglasevans

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

Using <details> in GitHub

Using `<details>` in GitHub