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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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Polymorphic Associations reversed

It's pretty easy to do polymorphic associations in Rails: A Picture can belong to either a BlogPost or an Article. But what if you need the relationship the other way around? A Picture, a Text and a Video can belong to an Article, and that article can find all media by calling @article.media

This example shows how to create an ArticleElement join model that handles the polymorphic relationship. To add fields that are common to all polymorphic models, add fields to the join model.

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VIM KEYBOARD SHORTCUTS

MOVEMENT

h        -   Move left
j        -   Move down
k        -   Move up
l        -   Move right
$        -   Move to end of line
0        -   Move to beginning of line (including whitespace)

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#!/bin/bash
# rev4 - changes suggested by KownBash https://www.reddit.com/r/bash/comments/5cxfqw/i_wrote_a_simple_video_to_gif_bash_script_thought/da19gjz/

# Usage function, displays valid arguments
usage() { echo "Usage: $0 [-f <fps, defaults to 15>] [-w <width, defaults to 480] inputfile" 1>&2; exit 1; }

# Default variables
fps=15
width=480

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# From http://garmoncheg.blogspot.com/2012/06/pretty-git-log.html
git config --global alias.lg "log --color --graph --pretty=format:'%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr) %C(bold blue)<%an>%Creset' --abbrev-commit --"

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require 'bundler/setup'
require 'eventmachine'
require 'open-uri'

EM.run do
  puts "main: #{Thread.current}"

  operation = proc {
    puts "defer operation: #{Thread.current}"
    sleep(20)

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Map	Action
<F1>	Causes Netrw to issue help
<cr>	Netrw will enter the directory or read the file
<del>	Netrw will attempt to remove the file/directory
-	Makes Netrw go up one directory
a	Toggles between normal display, hiding (suppress display of files matching g:netrw_list_hide) showing (display only files which match g:netrw_list_hide)
c	Make browsing directory the current directory
C	Setting the editing window
d	Make a directory

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tmux shortcuts & cheatsheet

start new:

tmux

start new with session name:

tmux new -s myname

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# litecoin.conf configuration file. Lines beginning with # are comments.


# Network-related settings:

# Run on the test network instead of the real litecoin network.
#testnet=0

# Connect via a socks4 proxy
#proxy=127.0.0.1:9050

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#!/usr/bin/env ruby
require 'net/telnet'

cache_dump_limit = 100
localhost = Net::Telnet::new("Host" => "localhost", "Port" => 11211, "Timeout" => 3)
slab_ids = []
localhost.cmd("String" => "stats items", "Match" => /^END/) do |c|
  matches = c.scan(/STAT items:(\d+):/)
  slab_ids = matches.flatten.uniq
end