mgwidmann

# Elixir has lazily evaluated enumerable objects that allow you
# to work with enumerable objects like lists either only as needed
# or infinitely.

# Start up iex to play around
$ iex

# Typical enumeration is done eagerly where the result is computed ASAP
iex> Enum.map(1..10, fn i -> i * 2 end)
[2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

mgwidmann

defmodule Ecto.Polymorphic do

  defmacro __using__(_) do
    quote do
      require Ecto.Schema
      import Ecto.Schema, except: [belongs_to: 2, belongs_to: 3]
      import unquote(__MODULE__)
    end
  end

mgwidmann

# The Elixir language is very extensible to allow for future additions or
# third party developers to take the language in directions that the original
# authors could not predict.
# 
# Lets start with understanding what an Elixir macro is
iex> quote do
...>   1 + 1
...> end
{:+, [context: Elixir, import: Kernel], [1, 1]}

mgwidmann

# Take all numbers from 0 to 50 million and sum every number from 0 to that number and sum those numbers
:timer.tc fn ->
  1..50_000_000
  |> Enum.map(& Enum.sum(0..&1))
  |> Enum.sum()
end
# Takes almost 2 minutes to run and returns the value 20,833,345,833,335,000,000
# => {108521694, 20833334583333350000000}

# Using task async stream, this can be done concurrently easily by just

mgwidmann

# machine 1
# start up with `iex --name m1@127.0.0.1 --cookie greeter`
# This isn't really necessary but it won't hurt anything
Node.connect :"m1@127.0.0.1"

# All `Node.connect/1` calls can go to the same machine and every machine 
# in the cluster will automatically be connected.

# machine 2
# start up with `iex --name m2@127.0.0.1 --cookie greeter`

mgwidmann

# To show hot code uploading, we first need to build a simple phoenix project so we can see it happen in real time.

# Start by making a new phoenix project
$ mix phoenix.new hotcode

# Go into the directory
$ cd hotcode

# Add exrm dependency to mix.exs file
{:exrm, "~> 1.0.3"}

mgwidmann

# The golden trinity of Erlang is the secret sauce behind what makes
# Elixir a strong choice for any backend application and/or system.

# https://tkowal.wordpress.com/2015/10/20/failing-fast-and-slow-in-erlang-and-elixir/

# The supervision and worker system, commonly referred to as OTP (Open
# Telecom Platform, which has nothing to do with telephony), is what
# gives Erlang/Elixir applications them a robust "self-healing" type
# property that makes them extremely fault tolerant.

mgwidmann

{} + "" == "()" // true

pow(2, 31).intValue + 1 > 0 // false

Set(1,2,3).sameElements(Set(3,2,1)) // false

Some(null).get // No exception :(, Some(null) should result in a None IMO

// Option objects might be null!!!
def safeOption(shouldBeSafe : Option[String]) : String = {

mgwidmann

# prices = [11, 7, 5, 8, 10, 9]
# => 5
# ALGO 1: BRUTE FORCE
# for each map to profit, find biggest number
#   11 => [-4, -6, -3, -1, -2]
#   7  => [-2, 1, 3, 2]
#   5  => [3, 5, 4]
#   8  => [2, 1]
#   10 => [-1]
#

mgwidmann

# Assuming we have some code like this
defmodule Processor do
  # A lot of code uses the following format, and its a good way to write code
  # However, when we have potential failures at each step things get complicated
  def process(user, meta) do
    user
    |> verify_authenticity(meta[:credentials])
    |> process_payment(meta[:charges])
    |> issue_resource
    |> generate_response