Peter Leonov peter-leonov

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

There are many (old) clients available:

https://github.com/tpitale/legato (active, supports API v3)
https://github.com/activenetwork/gattica
https://github.com/vigetlabs/garb

The Google Analytics API is at v3 (at time of writing).

This example uses Google's Ruby API client to access Analytics. Use https://github.com/google/google-api-ruby-client (Google supported).

	/* ----------------------------------------- *
	Lazy List Implementation
	* ----------------------------------------- */

	// Haskell-like infinite List, implemented with es6 generators

	// Lazyness lets you do crazy stuff like
	List.range(0, Infinity)
	.drop(1000)
	.map(n => -n)

	# get hex color of pixel
	# implementation of answer here http://stackoverflow.com/questions/8894194/retrieving-the-hex-code-of-the-color-of-a-given-pixel
	# solution to 'undefined method for MiniMagick::CommandBuilder in mini_magick'
	require 'mini_magick'
	module MiniMagick
	class Image
	def pixel_at(x, y)
	run_command("convert", "#{path}[1x1+#{x.to_i}+#{y.to_i}]", 'txt:').split("\n").each do \|line\|
	return $1 if /^0,0:.*(#[0-9a-fA-F]+)/.match(line)
	end