Thinking Functionally with Elixir

In this presentation, I share some of my experience learning functional programming in Elixir and how to leverage its features like pure functions, pattern patching, the pipe operator and recursion to write readable and efficient programs for the BEAM.

Transcript

1. Thinking Functionally Carlos Souza - @caike Code School / Pluralsight with Elixir
2. Functional Programming
3. Elixir
4. Elixir = Erlang VM (BEAM)
5. Elixir = Erlang VM (BEAM) movie: "Erlang - The Movie" Erlang: The Movie
7. My Life The CompSci Years
8. The Comp Sci Years #1
 Learn to 
 Learn New Things
9. The Comp Sci Years PROLOG
 Describe the problem and not the solution
10. A Taste of Prolog (@the_thagomizer)
11. Paradigms
12. Paradigms #1
 Learn to 
 Learn New Things
13. Paradigms #2 
 Forget What
 You Know
14. Paradigms
15. Paradigms conf = "ATO"
16. Functional Programming
17. Functional Programming - Pure Functions - Pattern Matching - Recursion
18. Functional Programming - Pure Functions - Pattern Matching - Recursion
19. Pure Functions - Pure Functions - Pattern Matching - Recursion
20. Two Rules of Pure Functions #1 - Return value should rely 
 entirely on arguments #2 - No side effects
21. Pure Functions
22. Pure Functions
23. Pure Functions How many in the basket ?
24. Pure Functions
25. Pure Functions I place in an empty
 basket and eat . 
 
 How many are left ?
26. Pure Functions
27. #1 - Return value should rely 
 entirely on arguments #2 - No side effects Two Rules of Pure Functions
28. Pure Functions Pure Functions defmodule Account do def balance(initial, spending) do initial - spending end end
29. Pure Functions Pure Functions defmodule Account do def balance(initial, spending) do initial - spending end end IO.puts 800 Account.balance(1000, 200)
30. Pure Functions vs. Objects account.currentBalance() vs. Account.balance(1000, 200)
31. Pure Functions Invoke function f on data x Invoke function g on the return value of function f on data x, and on data y f(x) g(f(x), y) j(i(h(g(f(x),y),z))) Now this is getting silly...
32. It’s Hard to Read “From the Inside Out” defmodule Account do def balance(initial, spending) do interest(discount(initial, 10), 0.1) end def discount(total, amount) do ... end def interest(total, rate) do ... end end
33. Piping Functions - |> defmodule Account do def balance(initial, spending) do discount(initial, 10) |> interest(0.1) end ... end defmodule Account do def balance(initial, spending) do discount(initial, 10) |> interest(0.1) |> format("$") end ... end read from left to righ new functions added to the end
34. Piping Functions the Elixir style - |> defmodule Account do def balance(initial, spending) do initial |> discount(10) |> interest(0.1) |> format("$") ... end end
35. Reading contents from a CSV file defmodule Budget do def list_transactions do File.read("transactions.csv") |> parse_file |> filter |> normalize |> sort |> print end ... end https://github.com/codeschool/budget-elixir
36. Pattern Matching - Pure Functions - Pattern Matching - Recursion
37. Pattern Matching Primitives conf = "ATO"
38. BrookeSam Brooke, Sam Elements from the list on the right... ...are a perfect match against those from the list on the left. users = ["Brooke", "Sam"] IO.puts users [first, second] = users IO.puts "#{first}, #{second}" Pattern Matching Lists - [ ]
39. Splitting Lists with [head|tail ] [head|tail] = ["Brooke", "Sam", "Niki"] "Brooke" ["Sam", "Nikki"]
40. Pattern Matching Tuples - { } {:ok, content} {:ok, "some content"} {:error, :enoent} Reading a file File.read("transactions.csv") =
41. File.read("transactions.csv") Reading Return Tuples {:error, error} file exists file doesn't exist {:ok, content}
42. Pattern Matching in Functions defmodule Budget do def list_transactions do |> parse_file end ... end or takes ONE argument {:ok, content} {:error, error} File.read("transactions.csv")
43. Pattern Matching in Functions No IF statement! defmodule Budget do ... 
 def parse_file({:ok, content}) do
 ... end 
 def parse_file({:error, error}) do ... end end
44. Pattern Matching Maps - %{ } empty variables are populated person = %{ "name" => "Brooke", "age" => 42 } = person , "age" => age matches keys on the right %{ "name" => name }
45. Pattern Matching Portions of Maps - %{ } person = %{ "name" => "Brooke", "age" => 42 } only reads portion of the map %{ "name" => name } = person
46. Pattern Matching Nested Maps - %{ } person = %{ "name" => "Brooke", "address" => %{ "city" => "Orlando", "state" => "FL"}} %{ "address" => %{ "state" => state }} = person matching on portion of the nested keys
47. Pattern Matching in Phoenix defmodule FireStarterWeb.VideoController do ... def show( ) do video = Repo.get(Video, id) render conn, "show.html", video: video end end Phoenix is MVC Elixir for the web. pattern matching! conn, %{"id" => id}
48. Pattern Matching in the wild pattern matching! https://github.com/mschae/cors_plug
49. Pattern Matching Everywhere
50. Recursion - Pure Functions - Pattern Matching - Recursion
51. Recursion "Recently refreshed sourdough, bubbling
 through fermentation: the recipe calls for 
 some sourdough left over from the last 
 time the same recipe was made." From https://en.wikipedia.org/wiki/Recursion:
52. Two Cases for Recursion All recursive functions involve the following two cases (or two clauses): 1. The base case or terminating scenario, 
 where the function does NOT invoke itself. 2. The recursive case, where computation 
 happens and the function invokes itself.
53. Recursive Factorial defmodule MyMath do def factorial(1) do 1 end def factorial(n) do n * factorial(n - 1) end end MyMath.factorial(3) #=> 6 MyMath.factorial(4) #=> 24 terminating
 scenario recursive case
56. Recursion [%{"name" => "Cyle Larin", "position" => "forward"}, %{"name" => "Antonio Nocerino", "position" => "midfielder"}, %{"name" => "Joe Bendik", "position" => "goalkeeper"}, %{"name" => "Jason Kreis", "position" => "coach"}] %{"name" => "Joe Bendik", "position" => "goalkeeper"} Listing players from Orlando City Soccer
57. Recursion defmodule SoccerTeam do def list_all() do end def get_goalie() do end end SoccerTeam.list_all SoccerTeam.get_goalie
58. Recursion defmodule SoccerTeam do def list_all() do end end SoccerTeam.list_all
59. Recursion defmodule SoccerTeam do use HTTPoison.Base def list_all() do url = "https://..." get_url(url) |> parse end defp parse( ) do end end %{status_code: 200, body: json_response} {:ok, list } = Poison.Parser.parse(json_response) list
60. Recursion [%{"name" => "Cyle Larin", "position" => "forward"}, %{"name" => "Antonio Nocerino", "position" => "midfielder"}, %{"name" => "Joe Bendik", "position" => "goalkeeper"}, %{"name" => "Jason Kreis", "position" => "coach"}] A list of maps
61. Recursion %{"name" => "Joe Bendik", "position" => "goalkeeper"} Finding the goalkeeper
62. Recursion defmodule SoccerTeam do def get_goalie() do end end SoccerTeam.get_goalie
63. Recursion defmodule SoccerTeam do use HTTPoison.Base def get_goalie() do url = "https://..." get_url(url) |> parse end end |> find_goalie
64. Recursion defmodule SoccerTeam do ... def find_goalie([%{"position" => "goalkeeper"} = head|_]) do head end def find_goalie([_|tail]) do find_goalie(tail) end def find_goalie([]) do raise "Error. No goalie found" end end No for loop No while statement
65. Recursive Factorial defmodule MyMath do def factorial(1) do 1 end def factorial(n) do n * factorial(n - 1) end end MyMath.factorial(10_000_000)
66. Recursion with no TCO
67. Recursive Factorial defmodule MyMath do def factorial(1) do 1 end def factorial(n) do n * factorial(n - 1) end end MyMath.factorial(10_000_000) not the LAST expression in this function
68. Recursive Factorial defmodule MyMath do def factorial(1) do 1 end def factorial(n) do n * factorial(n - 1) end end MyMath.factorial(10_000_000) the LAST expression in this function
69. Tail Call Optimization MyMath.factorial(10_000_000) defmodule MyMath do def factorial(1, acc) do acc end def factorial(n, acc) do factorial(n-1, n * acc) end def factorial(n) do factorial(n, 1) end end
70. Tail Call Optimization
71. That was a lot! - Functional Programming - Elixir - Pure Functions, Pattern Matching and 
 Recursion - Recursion with TCO FTW
72. Resources codeschool.com pragprog.com
73. Thinking Functionally with Elixir Thank you! # Carlos Souza - @caike Code School / Pluralsight