cheeyeo

defmodule ExUnit.Lets do
  defmacro __using__([]) do
    quote do
      import ExUnit.Lets
    end
  end

  defmacro let(name, expr) do
    if match?([do: _], expr) do
      expr = expr[:do]

cheeyeo

See https://www.youtube.com/watch?v=4_RJu_TrqO0&feature=youtu.be&t=8h6m40s

$ ruby dilute.rb fib.rb
def fi  n
  if n < 3
    1
  else
    fib(n-1  +  ib(n
 end

cheeyeo

Server scripts

This is the source for the scripts discussed in https://robots.thoughtbot.com/improving-user-experience-with-shell-scripts

Both scripts are in the bin/ directory of the repo that contains all the markdown documents for blog posts. Users run bin/server and everything is automatically set up for them to view a local preview of the blog. bin/server-setup is a dependency of bin/server and is never run directly by users.

Maitre-d is the name of the "blog engine" discussed in the article.

cheeyeo

#!/usr/bin/env ruby
#/ Usage: <progname> [options]...
#/ How does this script make my life easier?
# ** Tip: use #/ lines to define the --help usage message.
$stderr.sync = true
require 'optparse'

# default options
flag    = false
option  = "default value"

cheeyeo

module GitHub
  module CSP
    # Public: Constants for CSP keywords
    NONE          = "'none'".freeze
    SELF          = "'self'".freeze
    UNSAFE_INLINE = "'unsafe-inline'".freeze
    UNSAFE_EVAL   = "'unsafe-eval'".freeze

    # Public: Constants for CSP directive names
    BASE_URI        = "base-uri".freeze

cheeyeo

import { Component } from "React";

export var Enhance = ComposedComponent => class extends Component {
  constructor() {
    this.state = { data: null };
  }
  componentDidMount() {
    this.setState({ data: 'Hello' });
  }
  render() {

cheeyeo

class Importer
  def parse_csv_file(csv_file)
    File.open(csv_file) do |file|
      ActiveRecordModel.transaction do
        import_csv_stream(file)
      end
    end
  end
end

cheeyeo

Transactions

As your business logic gets complex you may need to implement transactions. The classic example is a bank funds transfer from account A to account B. If the withdrawal from account A fails then the deposit to account B should either never take place or be rolled back.

Basics

All the complexity is handled by ActiveRecord::Transactions. Any model class or instance has a method named .transaction. When called and passed a block, that block will be executed inside a database transaction. If there's an exception raised, the transaction will automatically be rolled back.

Example

cheeyeo

daemon off;
# Heroku dynos have at least 4 cores.
worker_processes <%= ENV['NGINX_WORKERS'] || 4 %>;

events {
  use epoll;
  accept_mutex on;
  worker_connections 1024;
}

cheeyeo

# A small DSL for helping parsing documents using Nokogiri::XML::Reader. The
# XML Reader is a good way to move a cursor through a (large) XML document fast,
# but is not as cumbersome as writing a full SAX document handler. Read about
# it here: http://nokogiri.org/Nokogiri/XML/Reader.html
# 
# Just pass the reader in this parser and specificy the nodes that you are interested
# in in a block. You can just parse every node or only look inside certain nodes.
# 
# A small example:
#