Elixir: A Talk For College Students

Slides for a talk I gave on CodeWeek 2015 (http://cesium.di.uminho.pt/codeweek15)

The talk was divided into 2 parts: the first was a small introduction to the language, with lots of small examples from the official Getting Started guide. The second part was a small in-depth guide to OTP and the actor model.

All code examples are available on https://github.com/frmendes/elixir-intro

I lost the references I had saved for the pictures. Contact me if I used your photos and you want to be referenced.

Transcript

1. ELIXIR
   a talk for college students
   CodeWeek 15
   Informatics Dept. , UMinho
   

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2. STORYTIME
   

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3. 23/09/2011

   

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4. 23/09/2011

   ONE MILLION TCP CONNECTIONS
   

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5. 23/09/2011

   ONE MILLION TCP CONNECTIONS
   ON A SINGLE NODE
   

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6. 23/09/2011

   ONE MILLION TCP CONNECTIONS
   ON A SINGLE NODE
   WITH RESOURCES TO SPARE
   

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7. 23/09/2011

   ONE MILLION TCP CONNECTIONS
   ON A SINGLE NODE
   WITH RESOURCES TO SPARE
   

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8. • FUNCTIONAL
   • FAULT TOLERANT
   • DISTRIBUTED & SCALABLE
   • PARALLEL
   • HOT CODE SWAPPING
   

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9. • LIGHTWEIGHT PROCESSES
   • ACTOR MODEL
   • TRIED AND TESTED VM
   • GARBAGE COLLECTION
   • NETWORK PROTOCOLS
   

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11. ERLANG
    iS
    AWESOME
    

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12. ERLANG
    iS
    AWESOME
    … but why Elixir, then?
    

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13. github: @frmendes
    everywhere else: @fribmendes
    my awesome sister who
    doesn’t code but it’s all good
    ‘cause she doesn’t like Java
    

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16. love me, please
    lol, not my cat
    

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17. ELIXIR
    everything erlang has to offer
    

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18. beautiful syntax
    ELIXIR
    

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19. powerful libraries
    ELIXIR
    

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20. metaprogramming \m/
    ELIXIR
    

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21. awesome DSLs
    ELIXIR
    

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22. mix ecosystem
    ELIXIR
    

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23. ELIXIR
    AS A LANGUAGE
    

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24. iex> 1 # integer
    iex> 0x1F # integer
    iex> 1.0 # float
    iex> true # boolean
    iex> :atom # atom / symbol
    iex> "elixir" # string
    iex> [1, 2, 3] # list
    iex> {1, 2, 3} # tuple
    ELIXIR
    

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25. LISTS
    

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26. iex> [1, 2, true, 3]

    [1, 2, true, 3]
    iex> tuple = {:ok, "hello"}
    {:ok, “hello”}
    ELIXIR
    linked list
    tuple - contiguous memory
    

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27. iex> tuple = {:ok, "hello"}
    {:ok, “hello”}
    iex> put_elem(tuple, 1, "world")
    {:ok, “world”}
    iex> tuple
    {:ok, “hello”}
    ELIXIR
    

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28. iex> tuple = {:ok, "hello"}
    {:ok, “hello”}
    iex> put_elem(tuple, 1, "world")
    {:ok, “world”}
    iex> tuple
    {:ok, “hello”}
    ELIXIR
    immutability
    aka “lolno.”
    

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29. PATTERN MATCHING
    

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30. iex> x = 1
    1
    iex> x
    1
    iex> 1 = x
    1
    ELIXIR
    

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31. iex> x = 1
    1
    iex> x
    1
    iex> 1 = x
    1
    ELIXIR
    x = 1?
    what is 1?
    1 is 1
    x is 1
    

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32. iex> x = 1
    1
    iex> x
    1
    iex> 1 = x
    1
    ELIXIR
    I know what’s 1! it’s x!
    

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33. iex> x = 1
    1
    iex> 2 = x
    ** (MatchError) no match of right hand side value: 1
    iex> 1 = y
    ** (RuntimeError) undefined function: y/0
    ELIXIR
    What is 1?
    

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34. iex> x = 1
    1
    iex> 2 = x
    ** (MatchError) no match of right hand side value: 1
    iex> 1 = y
    ** (RuntimeError) undefined function: y/0
    ELIXIR
    I don’t know y so y can’t be 1
    

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35. iex> [head | tail] = [1, 2, 3]
    [1, 2, 3]
    iex> head
    1
    iex> tail
    [2, 3]
    ELIXIR
    

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36. iex> x = 1
    1
    iex> ^x = 2
    ** (MatchError) no match of right hand side value: 2
    ELIXIR
    

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37. int x = 1;
    if (x == 1)
    y = 2;
    JAVA
    

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38. int x = 1;
    if (x == 1)
    y = 2;
    JAVA
    x = 1
    y = 2 if x = 1
    RUBY
    

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39. int x = 1;
    if (x == 1)
    y = 2;
    JAVA
    x = 1
    y = f x
    where f 1 = 2
    HASKELL
    x = 1
    y = 2 if x = 1
    RUBY
    

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40. int x = 1;
    if (x == 1)
    y = 2;
    JAVA
    x = 1
    y = f x
    where f 1 = 2
    HASKELL
    x = 1
    y = 2 if x = 1
    RUBY
    x = 1
    {y, ^x} = {2, 1}
    ELIXIR
    

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41. iex> 'hello' == "hello"
    false
    iex> [104, 101, 108, 108, 111]
    'hello'
    ELIXIR
    

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42. iex> 'hello' == "hello"
    false
    iex> [104, 101, 108, 108, 111]
    'hello'
    ELIXIR
    wait, what?
    

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43. STRINGS
    

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44. STRINGS
    UTF-8
    

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45. STRINGS
    UTF-8
    
    

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46. “”.length
    ?
    

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47. “”.size
    ?
    

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48. “”.size
    4 bytes each emoji
    

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49. “baffle”.length
    ?
    

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50. “baffle”.size
    ?
    

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51. “baffle”.size
    length 4
    size 6
    

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52. string types are hard
    

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53. string types usually suck
    

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54. string types usually suck
    usually
    

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55. “”.length();
    > 8
    “baffle”.length();
    > 4
    JAVA
    ffl is a single unicode character
    

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56. new StringBuilder(“baffle”).reverse();
    > “efflab”
    “baffle”.toUpperCase();
    > “BAFFLE”
    JAVA
    

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57. “”.length
    > 4
    “baffle”.length
    > 4
    RUBY
    

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58. “baffle”.reverse
    > “efflab”
    “baffle”.upcase
    > “BAfflE”
    RUBY
    

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59. def
    puts “it works!”
    end
    
    > “it works!”
    RUBY
    UTF-8 file encoding
    means we get to write
    awesome,
    readable code!
    

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60. iex> byte_size “”
    16
    iex> String.length “”
    4
    ELIXIR
    

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61. iex> byte_size “baffle”
    6
    iex> String.length “baffle”
    4
    ELIXIR
    

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62. iex> String.codepoints “”
    [“”, “”, “”, “”]
    iex> String.codepoints “baffle”
    [“b”, “a”, “ffl”, “e”]
    iex> to_char_list “baffle”
    [98, 97, 64260, 101]
    ELIXIR
    

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63. iex> String.reverse “baffle”
    “efflab”
    iex> String.upcase “baffle”
    “BAFFLE”
    ELIXIR
    

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64. iex> "he" <> "llo"
    “hello"
    iex> "he" <> rest = "hello"
    “hello"
    iex> rest
    "llo"
    ELIXIR
    Concatenation operator for
    pattern matching
    

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65. BINARIES
    

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66. iex> <<0, 1, 2, 3>>
    <<0, 1, 2, 3>>
    iex> byte_size <<0, 1, 2, 3>>
    4
    ELIXIR
    “basically” a byte array
    

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67. iex> <<256>>
    <<0>>
    iex> <<256 :: size(16)>>
    <<1, 0>>
    ELIXIR
    truncation
    “yo, use 2 bytes!”
    

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68. iex> <<256 :: utf8>>
    "Ā"
    ELIXIR
    treat as codepoint
    

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69. iex> <<1 :: size(1)>>
    <<1::size(1)>>
    iex> <<2 :: size(1)>>
    <<0::size(1)>>
    ELIXIR
    truncation
    use a single bit
    

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70. iex> is_binary(<< 1 :: size(1)>>)
    false
    iex> is_bitstring(<< 1 :: size(1)>>)
    true
    ELIXIR
    

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71. iex> bit_size(<< 1 :: size(1)>>)
    1
    iex> byte_size(<< 1 :: size(1)>>)
    1
    ELIXIR
    Erlang VM still allocates 1 byte
    

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72. iex> byte_size(<< 1 :: size(8)>>)
    1
    iex> byte_size(<< 1 :: size(9)>>)
    2
    ELIXIR
    byte allocation
    

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73. KEYWORD LISTS
    

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74. iex> list = [{:a, 1}, {:b, 2}]
    [a: 1, b: 2]
    iex> list == [a: 1, b: 2]
    true
    iex> list[:a]
    1
    ELIXIR
    special keyword list syntax
    

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75. iex> new_list = [a: 0] ++ list
    [a: 0, a: 1, b: 2]
    iex> new_list[:a]
    0
    ELIXIR
    Allows
    repeated keys
    

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76. iex> new_list = [a: 0] ++ list
    [a: 0, a: 1, b: 2]
    iex> new_list[:a]
    0
    ELIXIR
    first value of the lookup
    

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77. iex> if(false, [do: :this, else: :that])
    :that
    ELIXIR
    

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78. query = from w in Weather,
    where: w.prcp > 0,
    where: w.temp < 20,
    select: w
    ELIXIR
    

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79. MAPS
    

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80. Map map = new HashMap<>();
    map.put(“a”, 1);
    map.put(“b”, 2);
    JAVA
    

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81. Map map = new HashMap<>();
    map.put(“a”, 1);
    map.put(“b”, 2);
    JAVA
    Short version is long
    

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82. Map map = new HashMap<>();
    map.put(“a”, 1);
    map.put(“b”, 2);
    JAVA
    Auto-boxing
    

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83. map = {a: 1, b: 2}
    other_map = {a: 1, 2 => :b}
    RUBY
    

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84. map = %{a: 1, b: 2}
    other_map = %{a: 1, 2 => :b}
    ELIXIR
    

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85. iex> other_map[2]
    :b
    iex> %{a: a} = other_map
    %{a: 1, 2 => :b}
    iex> a
    1
    ELIXIR
    Elegant pattern matching
    

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86. iex> %{b: b} = other_map
    ** (MatchError) no match of right hand side value:
    %{2 => :b, :a => 1}
    iex> other_map[:b]
    nil
    ELIXIR
    Elegant pattern matching failing
    No error
    

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87. LOGICAL OPERATORS
    

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88. 1> true and false.
    false
    2> false or true.
    true
    3> not (true and true)
    false
    ERLANG
    

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89. 1> true and false.
    false
    2> false or true.
    true
    3> not (true and true)
    false
    ERLANG
    Always evaluate on each side
    

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90. 1> true andalso false.
    false
    2> false orelse true.
    true
    ERLANG
    Short-circuit operators
    

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91. iex> true and true
    true
    iex> false or is_atom(:example)
    true
    ELIXIR
    Short-circuit operators
    

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92. iex> false and raise("This error will
    never be raised")
    false
    iex> true or raise("This error will
    never be raised")
    true
    ELIXIR
    

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93. CONTROL FLOW
    

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94. int x = 1;
    switch(x) {
    case 1:
    System.out.println(“Will match”);
    break;
    default:
    System.out.println(“Doesn’t match”);
    }
    JAVA
    

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95. int x = 1;
    switch(x) {
    case 1:
    System.out.println(“Will match”);
    break;
    default:
    System.out.println(“Doesn’t match”);
    }
    JAVA
    No extra conditions
    

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96. iex> case {1, 2, 3} do
    ...> {4, 5, 6} ->
    ...> "This clause won't match"
    ...> {1, x, 3} ->
    ...> "This clause will match and bind x to 2"
    ...> _ ->
    ...> "This clause would match any value"
    ...> end
    "This clause will match and bind x to 2"
    ELIXIR
    

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97. iex> case {1, 2, 3} do
    ...> {4, 5, 6} ->
    ...> "This clause won't match"
    ...> {1, x, 3} ->
    ...> "This clause will match and bind x to 2"
    ...> _ ->
    ...> "This clause would match any value"
    ...> end
    "This clause will match and bind x to 2"
    ELIXIR
    binds x to 2
    

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98. iex> case {1, 2, 3} do
    ...> {4, 5, 6} ->
    ...> "This clause won't match"
    ...> {1, x, 3} ->
    ...> "This clause will match and bind x to 2"
    ...> _ ->
    ...> "This clause would match any value"
    ...> end
    "This clause will match and bind x to 2"
    ELIXIR
    but x is only valid in this scope
    

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99. iex> x = 1
    1
    iex> case 10 do
    ...> ^x -> "Won't match"
    ...> _ -> "Will match"
    ...> end
    "Will match"
    ELIXIR
    Pin operator allows comparison
    

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100. iex> case {1, 2, 3} do
     ...> {1, x, 3} when x > 0 ->
     ...> "Will match"
     ...> _ ->
     ...> “Won’t match"
     ...> end
     "Will match"
     ELIXIR
     Scoped assignment allows guards
     

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101. iex> if true do
     ...> "This works!"
     ...> end
     “This works!”
     ELIXIR
     

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102. iex> unless false do
     ...> "This works!"
     ...> end
     “This works!”
     ELIXIR
     

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103. iex> if nil do
     ...> "This won't be seen"
     ...> else
     ...> "This will"
     ...> end
     "This will"
     ELIXIR
     

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104. iex> if nil do
     ...> "This won't be seen”
     ...> else if
     ...> "This is an error"
     ...> else
     ...> "This will"
     ...> end
     "This will"
     ELIXIR
     

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105. iex> if nil do
     ...> "This won't be seen”
     ...> else if
     ...> "This is an error"
     ...> else
     ...> "This will"
     ...> end
     "This will"
     ELIXIR
     

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106. iex> if(false, [do: :this, else: :that])
     :that
     ELIXIR
     

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107. iex> cond do
     ...> 2 + 2 == 5 ->
     ...> "This is never true"
     ...> 2 * 2 == 3 ->
     ...> "Nor this"
     ...> true ->
     ...> "This is always true (equivalent
     to else)"
     ...> end
     ELIXIR
     

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108. FUNCTIONS
     

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109. def add(x, y) do
     x + y
     end
     ELIXIR
     Needs to be inside a module
     

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110. def add(x, 0) do
     x
     end
     ELIXIR
     Arguments can do pattern matching
     

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111. def add(x, y) when x == 0 do
     y
     end
     ELIXIR
     And we can use guards
     

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112. add2 = fn
     x, y when x == 0 -> y
     x, 0 -> x
     x, y -> x + y
     end
     ELIXIR
     Anonymous function
     

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113. iex> Arithmetic.add(1, 3)
     4
     iex> add2.(-1, 0)
     -1
     ELIXIR
     Module name
     

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114. arity identifies functions
     

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115. def add(x, y) do
     x + y
     end
     def add(x) do
     x + 1
     end
     ELIXIR
     add/1
     add/2
     

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116. add2 = fn
     x, y -> x + y
     x -> 0
     end
     ** (SyntaxError) cannot mix clauses with different
     arities in function definition
     ELIXIR
     

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117. anonymous functions are closures
     

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118. iex> x = 1
     iex> add_x = fn y -> x + y end
     iex> add_x.(2)
     3
     ELIXIR
     

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119. x = 1
     def add_x(y) do
     x + y
     end
     ELIXIR
     

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120. x = 1
     def add_x(y) do
     x + y
     end
     ELIXIR
     compile error
     

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121. x = 1
     def add_x(y) do
     x + y
     end
     ELIXIR
     each function definition has a blank scope
     

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122. anonymous functions are callable
     

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123. iex> add_one = fn x -> x + 1 end
     iex> Enum.map([1, 2, 3, 4], add_one)
     [2, 3, 4, 5]
     ELIXIR
     

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124. iex> defmodule Arith do
     ...> def add_two(x), do: x + 2
     ...> end
     iex> Enum.map([1, 2, 3, 4],
     &Arith.add_two/1)
     [2, 3, 4, 5]
     ELIXIR
     capture syntax
     

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125. ENUMS & STREAMS
     

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126. iex> add_one = fn x -> x + 1 end
     iex> Enum.map([1, 2, 3, 4], add_one)
     [2, 3, 4, 5]
     ELIXIR
     Enum module
     

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127. iex> 0..99 |> Enum.map(&(&1 + 1))
     |> Enum.filter(&Integer.is_odd/1)
     |> Enum.sum
     ELIXIR
     

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128. iex> 0..99 |> Enum.map(&(&1 + 1))
     |> Enum.filter(&Integer.is_odd/1)
     |> Enum.sum
     ELIXIR
     pipe operator - similar to unix pipe
     

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129. iex> 0..99 |> Enum.map(&(&1 + 1))
     |> Enum.filter(&Integer.is_odd/1)
     |> Enum.sum
     ELIXIR
     capturing a function
     

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130. iex> 0..99 |> Enum.map(&(&1 + 1))
     |> Enum.filter(&Integer.is_odd/1)
     |> Enum.sum
     ELIXIR
     first argument passed to the function
     

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131. iex> 0..99 |> Enum.map(&(&1 + 1))
     |> Enum.filter(&Integer.is_odd/1)
     |> Enum.sum
     ELIXIR
     capture module function
     

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132. iex> 0..99 |> Enum.map(&(&1 + 1))
     |> Enum.filter(&Integer.is_odd/1)
     |> Enum.sum
     ELIXIR
     Enum is eager: every operation generates an intermediate list
     

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133. iex> 0..99 |> Stream.map(&(&1 + 1))
     |> Stream.filter(&Integer.is_odd/1)
     |> Enum.sum
     ELIXIR
     Stream is lazy: every operation returns another stream
     

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134. iex> 0..99 |> Stream.map(&(&1 + 1))
     |> Stream.filter(&Integer.is_odd/1)
     |> Enum.sum
     ELIXIR
     Enum is used to make the calculation
     

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135. iex> 0..99 |> Stream.map(&(&1 + 1))
     |> Stream.filter(&Integer.is_odd/1)
     |> Enum.sum
     ELIXIR
     Enum is used to make the calculation
     

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136. iex> 0..99 |> Stream.map(&(&1 + 1))
     |> Stream.filter(&Integer.is_odd/1)
     |> Enum.sum
     ELIXIR
     Stream only carries a set of operations
     to make somewhere in the future
     

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137. iex> stream = Stream.cycle([1, 2, 3])
     iex> Enum.take(stream, 10)
     [1, 2, 3, 1, 2, 3, 1, 2, 3, 1]
     ELIXIR
     infinite set
     

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138. ELIXIR
     ACTOR MODEL & OTP
     

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139. PROCESSES
     

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140. ELIXIR PROCESSES
     ≠
     OS PROCESSES
     

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141. “An actor is an entity that receives messages and,
     according to those messages, can
     send more messages,
     create a finite number of actors and
     choose behaviour for processing the next message”
     - Carl Hewitt, 1973
     

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142. Actors are processes.
     Processes act upon messages.
     Each process has a mailbox.
     Messages are asynchronous and there are no guarantees
     regarding delivery.
     Each process has its own state, which is not shared.
     

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143. parent = self
     spawn fn -> send(parent, {:hello, self}) end
     receive do
     {:hello, pid} -> IO.puts “Hello #{inspect pid}”
     end
     

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144. what if…
     no one is listening?
     

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145. Actors are processes.
     Processes act upon messages.
     Each process has a mailbox.
     Messages are asynchronous and there are no guarantees
     regarding delivery.
     Each process has its own state, which is not shared.
     Each process has a mailbox.
     

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146. what if…
     we received an unexpected message?
     

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147. FUNCTIONAL PARADIGM™
     everything
     is immutable
     

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148. immutable
     ≠ stateless
     FUNCTIONAL PARADIGM™
     

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149. OOP
     behaviour
     CLASS
     state
     INSTANCE
     

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150. FP
     behaviour
     MODULE
     state
     PROCESS
     

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151. A SAMPLE QUEUE
     

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152. defmodule Queue do
     use GenServer
     def new do
     GenServer.start_link(Queue, [], [])
     end
     end
     

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153. def handle_cast({:put, value}, state) do
     {:noreply, state ++ [value]}
     end
     Server callbacks
     

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154. def handle_call(:poll, _from, []) do
     {:reply, nil, []}
     end
     def handle_call(:poll, _from, state) do
     [head|tail] = state
     {:reply, head, tail}
     end Server callbacks
     

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155. iex> {:ok, q} = Queue.new
     iex> GenServer.cast(q, {:put, 1})
     iex> GenServer.call(q, :poll)
     1
     

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156. def put(queue, value) do
     GenServer.cast(queue, {:put, value})
     end
     def poll(queue) do
     GenServer.call(queue, :poll)
     end Client callbacks
     

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157. iex> {:ok, q} = Queue.new
     iex> Queue.put(q, 1)
     iex> Queue.poll(q)
     1
     

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158. TASK
     

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159. “Tasks are processes meant to execute one
     particular action throughout their life-cycle,
     often with little or no communication with other
     processes.”
     - Elixir Docs, 2015
     

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160. FAILURES
     

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161. “The greatest advantage actor-based systems
     give us is accepting programmers make
     mistakes all the time and not all scenarios are
     testable.”
     - Me, right now
     

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162. fail
     fast
     

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163. let
     crash
     it
     

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164. try do
     raise "oops"
     rescue
     e in RuntimeError -> e
     end
     

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165. try do
     raise "oops"
     rescue
     e in RuntimeError -> e
     end
     don’t care about failures
     

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166. try do
     raise "oops"
     rescue
     e in RuntimeError -> e
     end
     use Supervisors instead
     

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167. try do
     raise "oops"
     rescue
     e in RuntimeError -> e
     end
     keep your code clean
     

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168. try do
     raise "oops"
     rescue
     e in RuntimeError -> e
     end
     keep your flow clean
     

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169. A SAMPLE CHAT
     

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170. def listen(port) do
     {:ok, socket} = :gen_tcp.listen(port,
     [:list, packet: :line,
     active: false,
     reuseaddr: true])
     acceptor(socket)
     end
     Server Module
     

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171. defp acceptor(socket) do
     {:ok, client} = :gen_tcp.accept(socket)
     handle_client(client)
     acceptor(socket)
     end
     Server Module
     

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172. defp handle_client(client) do
     client |> read() |> write(client)
     handle_client(client)
     end
     Server Module
     

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173. defp read(socket) do
     # 2nd param is byte length
     # 0 means receive all available bytes
     {:ok, data} = :gen_tcp.recv(socket, 0)
     data
     end
     Server Module
     

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174. defp write(msg, socket) do
     :gen_tcp.send(socket, msg)
     end
     Server Module
     

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175. what if…
     we want to echo multiple clients?
     

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176. def start do
     import Supervisor.Spec
     children = [
     supervisor(Task.Supervisor, [[name: Server.TaskSupervisor]]),
     worker(Task, [Server, :listen, [3000]])
     ]
     opts = [strategy: :one_for_one, name: ServerSupervisor]
     Supervisor.start_link(children, opts)
     end
     Server Module
     

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177. defp acceptor(socket) do
     {:ok, client} = :gen_tcp.accept(socket)
     handle_client(client)
     acceptor(socket)
     end
     Old Server Module
     

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178. defp acceptor(socket) do
     {:ok, client} = :gen_tcp.accept(socket)
     {:ok, pid} = Task.Supervisor.start_child(
     Server.TaskSupervisor, fn -> handle_client(client) end)
     # transferring the socket control to the new child
     :ok = :gen_tcp.controlling_process(client, pid)
     acceptor(socket)
     end New Server Module
     

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179. ELIXIR
     a talk for college students
     @frmendes
     @fribmendes
     

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