Elixir talk

ELIXIRGETTING STARTED WITH HIGHLY SCALABLE, SUPER SEXY SYSTEMS

INTRO

WHAT IS ELIXIR

▸ Erlang / Erlang Compatible

▸ Functional

▸ Ruby like Syntax

▸ Scalable

▸ Interactive Shell (REPL) and Compiled

▸ Able to run hundreds of thousands of processes on a single machine.

INTRO

WHAT IS ERLANG?

▸ Erlang is a programming language used to build massively scalable soft real-time systems with requirements on high availability.

▸ First appeared in 1986

▸ Distributed, Fault-Tolerant, High availability, Hot swappable.

▸ Erlang was designed with the aim of improving the development of telephony applications by Ericsson

▸ As Tim Bray, director of Web Technologies at Sun Microsystems, expressed in his keynote at OSCON in July 2008: If somebody came to me and wanted to pay me a lot of money to build a large scale message handling system that really had to be up all the time, could never afford to go down for years at a time, I would unhesitatingly choose Erlang to build it in.

INSTALL

LETS INSTALL

▸ Mac - Homebrew: brew install elixir

▸ Mac - MacPorts: sudo port install elixir

▸ Linux or Windows: http://elixir-lang.org/install.html

PACKAGE AND ENV MANAGEMENT

MIX

▸ Builds project skeleton - mix new project-name

▸ Compile projects - mix compile

▸ Manages dependencies - mix.esx file, install with mix deps.get

▸ def deps do

▸ [{:plug, "~> 1.0"}]

▸ end

▸ Test Runner - mix test

▸ mix help

SETUP

START A NEW PROJECT

▸ Start a new project

▸ cd to directory

▸ mix new learn

▸ cd learn

▸ mix test

▸ Lets look

GETTING STARTED

RUNNING

▸ iex (iex.bat on windows) - Interactive REPL

▸ elixir: runs a script (elixir simple.exs)

▸ elixirc: Compile to beam file and run.

▸ iex filename.exs

▸ inside iex > c “filename.ex”

▸ iex -S mix # include the current project into iex

GETTING STARTED

FILE TYPES

▸ .exs - For interpreted code.

▸ .ex - For compiled code.

▸ .beam - Compiled byte code via Erlang abstract format

DATA TYPES

BASIC TYPES

▸ Integers: 1

▸ Float: 0.1

▸ Boolean: true

▸ Symbol/atom: :name

▸ String: “hello”

▸ list (Linked list): [1, 2, 3]

▸ tuple: {1, 2, 3}

MATH

BASIC ARITHMETIC

▸ 1 + 2

▸ 5 * 5

▸ 10 / 2 (returns float)

▸ div(10, 2) rem(10, 2)

▸ round(4.2)

▸ trunc(4.6)

DATA TYPES

STRINGS

▸ x = “world”

▸ String interpolation “Hello #{x}”

▸ line break \n

▸ String.length("hello")

▸ String.upcase(“hello")

▸ ‘hello’ creates a character list, which is not what you expect.

DATA TYPES

LINKED LISTS

▸ [1, 2, true, 3]

▸ [1 | [2 | [3 |[]]]] # The pipe operator is the glue

▸ length [1, 2, 3]

▸ [1, 2, 3] ++ [4, 5, 6]

▸ [a | b] = [1, 2, 3, 4]

DATA TYPES

TUPLE

▸ tuple = { :ok, “elixir”, 2 }

▸ tuple_size tuple

▸ elem(tuple, 1)

▸ put_elem tuple, 1, “new”

▸ tuple

DATA TYPES

TUPLE OR LINKED LIST?

▸ Linked lists shouldn’t be used to retrieve items at an index

▸ Getting the length of a linked list is linear time

▸ Updating a list is fast as long as you are prepending

▸ Tuples are stored contiguously in memory, allowing easier access to single item or size

▸ Tuples are for small data sets

▸ Tuples are often used for returning multiple items from a function.

DATA TYPE

IMMUTABILITY

▸ Variables in elixir are just pointers.

▸ You can point a variable at a different block of memory, but you cannot change a block of memory that has been instantiated.

▸ Also you can pin a variable for pattern matching so it does not rebind - ^a = 1

▸ Functions cannot change the variable you pass into them.

DATA TYPE

IMMUTABLE EXERCISE

▸ Try this:

▸ tuple = var = {1, 2, 3}

▸ put_elem tuple, 1, “new”

▸ tuple

▸ var

▸ tuple = put_elem tuple, 1, “new”

▸ tuple

▸ var

ARRAYS?

WHERE IS THE ARRAY?

▸ Elixir has chosen to leave out some of the data types offered by Erlang. The array is one of the common data types developers may miss.

▸ Immutable programming is one reason it has been left out.

▸ A little array song and dance about memory, sorting and mutability.

▸ This is a highly debated topic in the community.

PATTERN MATCHING

=, I DON’T THINK IT MEANS WHAT YOU THINK

▸ x = 1

▸ 1 = x

▸ 2 = x

▸ {a, b, c} = {1, 2, 3}

▸ a

▸ {a, b, c} = {:hello, “world” } # check the number of args match

▸ {:ok, count} = {:error, 11} # ok is an atom, so it doesn't match

▸ {:ok, count} = {:ok, 9}

▸ count

DATA TYPES

KEYWORD LISTS

▸ [a: 10, b: 5] = [{:a, 10}, {:b, 5}]

▸ kwl = [{:name, “Cory”}, {:from, “Wisconsin”}, {:from, “California”}, {:from, “Pennsylvania”}]

▸ List.keyfind(kwl, “Cory”, 1) # find cory position 1

▸ List.keydelete(kwl, “Cory”, 1)

▸ kwl = List.keyreplace(kwl, :name, 0, {:first_name, “Cory”})

DATA TYPE

MAPS

▸ map = %{ name: “Cory”, from: “Wisconsin”, city: “Madison”}

▸ Map.keys map

▸ Map.values map

▸ map[:name]

▸ map.name

▸ Map.put map, :current, “Pennsylvania”

▸ %{ name: name_pointer} = map

DATA TYPES

MAPS OR KEYWORD LISTS

▸ Pattern match against the contents, for example matching a dictionary that has a key in it? - Map

▸ More than 1 entry with the same key? - Keyword module

▸ Guaranteed order? Keyword module

▸ Anything else - use a map

▸ (taken from Programming Elixir 1.2 book)

CONDITIONALS

CONDITIONAL LOGIC

▸ ==, !=, ===, !==, >, >=, <, <=

▸ and, or, not

▸ is_atom/1, is_float/1

▸ if true do: something

▸ unless true do: something

▸ if true do

▸ something

▸ else

▸ something else

▸ end

CONDITIONALS

THE WAR ON IF

▸ There is no “if else”

▸ Prefer guard functions, case or cond

CONDITIONALS

CASE

▸ You can use pattern matching in your cases, cases are usually returns from functions

▸ result = case {1, 2, 3} do

▸ {4, 5, 6} -> “This will not match”

▸ {1, 2, 3} -> “This will match and evaluate”

▸ end

CONDITIONALS

CONDITION

▸ The condition is useful when you need to check multiple possible conditions. Returns the first one that evaluates as true

▸ result = cond do

▸ 2 + 2 == 5 -> “This will fail”

▸ 2 + 2 == 4 -> “Suscess”

▸ true -> “A default case”

▸ end

FUNCTIONS

ANONYMOUS FUNCTION

▸ multiply = fn a, b -> a * b end

▸ multiply.(2, 3)

▸ double = fn a -> multiply.(a, 2) end

▸ functions define their own scope

▸ x = 1

▸ (fn -> x = 3 end).()

▸ x

▸ 1

MODULES

MODULES

▸ Group of functions

▸ String.length(“Chimera”)

▸ defmodule Chimera do

▸ def register(name) do

▸ do something cool

▸ end

▸ end

EXERCISE

BUILD A SIMPLE FUNCTION

▸ Test file - math_test.exs

▸ defmodule LearnTest do

▸ use ExUnit.Case

▸ test “Sum two numbers” do

▸ assert Learn.sum(1, 1) == 2

▸ end

▸ end

▸ Get this test to pass

FUNCTIONS

GUARD FUNCTIONS

▸ It is possible to have multiple functions with the same name that are executed based on some sort of pattern match or expression.

▸ pattern(%{ name: “” }), do: “Error name needed”

▸ pattern(%{name: name}) when name == “Cory”, do: “Hello Creator”

▸ pattern(%{ name: name}), do: “Hello #{name}”

FUNCTIONS

FUNCTIONS

▸ Guard Functions, great for recursion

▸ def MyMath do

▸ def sum([], total), do: total

▸ def sum([ head | tail ], total), do: sum(tail, head+total)

▸ end

FUNCTION

THE PIPE OPERATOR

▸ The |> operator passes data

▸ [from: "Wi", from: "CA"] |> List.keyfind(:from, 0)

▸ is the same as List.keyfind([from: "Wi", from: “CA”], :from, 0)

▸ Object Oriented “self” tangent here

SCHEMAS

HOW TO MODEL YOUR DATE

▸ Structs are a way to model complex common data structures.

▸ Structs are maps.

▸ Module can combine data and associated functions.

▸ defmodule User do

▸ defstruct name: nil, age: nil, address: nil

▸ def name(user), do: Map.fetch(user, :name)

▸ end

▸ user = %User{name: “Cory”, age: 37, address: “Pittsburgh” }

▸ User.name(user)

DEBUGGING TIPS

IO.INSPECT

▸ IO.inspect will print complex data types to STDOUT

▸ IO.inspect user

▸ Can be pipped into and returns what ever was piped into it.

▸ “Hellos World” |> String.replace(“s”, “”) |> IO.inspect |> String.split() |> IO.inspect

DEBUGGING

PRY

▸ Jump into a running session with an iex.pry

▸ require IEx;

▸ defmodule Example do

▸ def double_sum(x, y) do

▸ IEx.pry

▸ hard_work(x, y)

▸ end

▸ defp hard_work(x, y) do

▸ 2 * (x + y)

▸ end

▸ end

▸ iex -S mix

DEBUGGING

ERLANG DEBUGGER

▸ Erlang offers a built in breakpoint debugger.

▸ iex -S mix

▸ :debugger.start() # Start the process

▸ :int.ni(Learn) # Register the module

▸ :int.break(Learn, 3) # Set the breakpoint, line 3 of learn module

▸ Learn.sum(1, 2) # Run the code you want to debug

EXERCISES

REFACTOR

▸ Refactor this code, so you do not need to pass the total as an argument

▸ http://bit.ly/29WzscO

EXERCISES

FIZZ BUZZ

▸ Print the number 1-100 replacing multiples of 3 with the word “Fizz” and multiples of 5 with the word “Buzz”. If the word is a multiple of 5 and 3 then print FizzBuzz.

▸ ex:

▸ 1 2 Fizz 4 Buzz Fizz… 13 14 FizzBuzz

EXERCISES

BUILD A MAP TOOL

▸ Build a function that can accept a list and another function and excute the function on each item in the list returning a new list.

▸ MyMap.map([1, 2, 3], fn(item) -> item + 1 end)

▸ [2, 3, 4]

WHAT TO LEARN NEXT

NEXT TOPICS

▸ Iterating, mapping and recursion. Everything is a list.

▸ OTP - Abstraction layer for handling concurrency, supervising, fault tolerance, etc…

▸ Phoenix - Web Framework, Rails like

▸ Ecto - domain specific language for writing queries and interacting with databases

▸ Nerves - Embedded software for micro controllers.

▸ Meta-programming