Elixir in Elixir

Metaprogramming doesn't have to be scary. Elixir does it really well. Let me show you...

Transcript

1. Elixir Elixir
   In
   

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2. How much?
   

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3. It depends
   

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4. What is “Elixir”?
   

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5. Basics + STDLIB
   

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6. of
   Elixir is
   written in
   Elixir
   78%
   

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7. Compare to Ruby’s 44%
   

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8. Numbers? Meh
   

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9. if
   

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10. def
    

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11. |>
    

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12. Metaprogramming
    

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13. Code generation
    

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14. +BZ)BZFT
    IUUQTJBNWFSZDPNn!JBNWFSZ
    

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17. 8FEFWFMPQ
    

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18. 8FUFBDI
    

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19. 8FXSJUF
    

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20. “I’m speaking at
    ElixirConf!”
    

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21. “That’s nice. Where is it?”
    
    

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22. “Orlando.”
    

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23. “DISNEY IS THERE!!! CAN WE GO?!”
    
    

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24. “Ya, actually it’s at Disney.”
    

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25. “OMG!!!
    YOU’RE SPEAKING AT DISNEY?!!”
    

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26. “Haha, sort of” *interrupted*
    

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27. *on phone*
    “YA! He’s speaking at Disney!!
    We’re GOING!!!” *squeal*
    

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30. Metaprogramming
    

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32. programming
    Meta
    

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33. Working on Data
    

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34. data
    quantities on which
    operations are performed
    — Dictionary.app
    

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35. 4 + 2
    data
    

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36. +(4, 2)
    data
    

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37. Kernel.+(4, 2)
    

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38. The program is data
    

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39. Macros
    

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40. Macros are everywhere
    

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41. good macros are
    invisible
    

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42. defmodule ItTest do
    use ExUnit.Case
    test “works” do
    assert It.works?
    end
    end
    macros
    

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43. Where is the data?
    Program
    

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44. defmodule ItTest do
    use ExUnit.Case
    test “works” do
    assert It.works?
    end
    end
    

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45. defmodule ItTest do
    use ExUnit.Case
    test “works” do
    assert It.works?
    end
    end
    

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46. defmodule ItTest do
    use ExUnit.Case
    test “works” do
    assert It.works?
    end
    end
    

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47. defmodule ItTest do
    use ExUnit.Case
    test “works” do
    assert It.works?
    end
    end
    

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48. Expression
    macro
    Expression
    ✨
    ✨
    

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49. Expression?
    

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50. “Quoted” Elixir code
    

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51. {func, …, args}
    

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52. Abstract Syntax Tree
    

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53. +
    1 -
    2 3
    

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54. + 1 - 2 3
    ( ( ))
    func
    Args
    

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55. 1 + ( 2 - 3 )
    

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56. Args are quoted
    

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57. Expression.match?(:lol > :wat)
    # => false
    Expression.match?(:lol = :wat)
    # => true
    

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58. defmacro match?({:=, _, _}) do
    true
    end
    defmacro match?(_expr) do
    false
    end
    

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59. Expression.match?(:lol > :wat)
    # => false
    Expression.match?(:lol = :wat)
    # => true
    

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60. false
    # => false
    true
    # => true
    

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61. Must return quoted
    

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62. defmacro badmatch do
    {:=, [], [:lol, :wat]}
    end
    

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63. defmacro badmatch do
    quote do
    :lol = :wat
    end
    end
    

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64. Expression.badmatch
    # (MatchError)
    

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65. :lol = :wat
    # (MatchError)
    

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66. Quote
    

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67. {func, meta, args}
    

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68. {:=, [], [:lol, :wat]}
    

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69. quote do
    :lol = :wat
    end
    

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70. Sort of like strings…
    

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71. “1+1”
    

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72. quote(do: 1+1)
    

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73. quote do
    1+1
    end
    

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74. Return AST of Expression
    

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75. 2 - 3
    quote do
    end
    

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76. - 2 3
    {: , […], [ , ]}
    (- 2 3)
    

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77. quote do
    1 + (2 - 3)
    end
    

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78. {: , […], [ , {: , […], [ , ]}]}
    + 1 - 2 3
    (+ 1 (- 2 3))
    

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79. Easier to grok
    

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80. {:+, […], [1, {:-, […], [2, 3]}]}
    quote do
    1 + (2 - 3)
    end
    

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81. Quoted Literals
    

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82. quote do: “foo” # “foo”
    quote do: :foo # :foo
    quote do: 1 # 1
    quote do: [1] # [1]
    quote do: {1,2} # {1,2}
    quote do: [a: 1] # [a: 1]
    

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83. Unquote
    

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84. “Inject value in quote”
    

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85. Like string interpolation
    

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86. “Inject value into quoted string”
    

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87. name = “Sue”
    “hi name”
    # => “hi name”
    

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88. name = “Sue”
    “hi #{name}”
    # => “hi Sue”
    

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89. “Inject value into quoted Expression”
    

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90. num = 42
    # => 42
    quote do: 1 + num
    # => {:+, [], [1, {:num, [], :Elixir}]}
    

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91. num = 42
    # => 42
    quote do: 1 + unquote(num)
    # => {:+, [], [1, 42]}
    

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92. name = “Sue”
    “hi #{name}”
    # => “hi Sue”
    

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93. if
    

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94. if foo > 0 do
    IO.puts(“Pass!”)
    else
    IO.puts(“Fail.”)
    end
    

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95. if(…, do: …, else: …)
    

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96. if(…, [do: …, else: …])
    cases
    cond
    

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97. Truthy & Falsey
    

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98. false || nil
    Falsey
    

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99. anything else
    Truthy
    

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100. case … do
     x when x in [false, nil] -> …
     _ -> …
     end
     cond
     cases
     

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101. defmacro if(c, do: tc, else: fc) do
     quote do
     case unquote(c) do
     x when x in [false, nil] -> unquote(fc)
     _ -> unquote(tc)
     end
     end
     end
     cond cases
     cond
     cases
     

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102. if do
     else
     end
     foo > 0
     IO.puts(“Pass!”)
     IO.puts(“Fail.”)
     

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103. case do
     x when x in [false, nil] ->
     _ ->
     end
     foo > 0
     IO.puts(“Fail.”)
     IO.puts(“Pass!”)
     

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104. When to macro…
     

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105. #1 Don’t
     

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106. Write functions
     

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107. defmacro add(a, b) do
     quote do
     unquote(a) + unquote(b)
     end
     end
     

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108. def add(a, b) do
     a + b
     end
     

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109. More direct
     

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110. Less error-prone
     

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111. #2 Constants
     

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112. defmacro seconds_per_minute, do: 60
     defmacro minutes_per_hour, do: 60
     

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113. #3 DSL
     

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114. html do
     body do
     div class: “content” do
     p “Engaging content.”
     end
     end
     end
     

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115. #4 Hide details
     

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116. test “works” do
     assert It.works?
     end
     

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117. #5 Reduce boilerplate
     

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118. Language extension
     

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119. defmodule Lolwat do
     def lol do
     :wat
     end
     end
     

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120. :elixir_module.compile(Lolwat, {:def, [context: Elixir,
     import: Kernel], [{:lol, [context: Elixir], Elixir},
     [do: :wat]]}, [], __ENV__)
     

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121. :elixir_module.compile(Lolwat, {:def, [context: Elixir, import: Kernel], [{:lol, [context:
     Elixir], Elixir}, [do: :wat]]}, [], %{__struct__: Macro.Env, aliases: [], context: nil,
     context_modules: [Mex], export_vars: nil, file: "iex", function: nil, functions: [Mex:
     [expand_all: 2], "IEx.Helpers": [c: 1, c: 2, cd: 1, clear: 0, flush: 0, h: 0, i: 1, l: 1, ls: 0,
     ls: 1, nl: 1, nl: 2, pid: 1, pid: 3, pwd: 0, r: 1, recompile: 0, respawn: 0, v: 0, v: 1],
     Kernel: [!=: 2, !==: 2, *: 2, +: 1, +: 2, ++: 2, -: 1, -: 2, --: 2, /: 2, ===: 2, =~: 2, >: 2, >=: 2, abs: 1, apply: 2, apply: 3, binary_part: 3, bit_size: 1, byte_size:
     1, div: 2, elem: 2, exit: 1, function_exported?: 3, get_and_update_in: 3, get_in: 2, hd: 1,
     inspect: 1, inspect: 2, is_atom: 1, is_binary: 1, is_bitstring: 1, is_boolean: 1, is_float: 1,
     is_function: 1, is_function: 2, is_integer: 1, is_list: 1, is_map: 1, is_number: 1, is_pid: 1,
     is_port: 1, is_reference: 1, is_tuple: 1, length: 1, macro_exported?: 3, make_ref: 0, map_size:
     1, max: 2, min: 2, node: 0, node: 1, not: 1, pop_in: 2, put_elem: 3, put_in: 3, rem: 2, round:
     1, self: 0, send: 2, spawn: 1, spawn: 3, spawn_link: 1, spawn_link: 3, spawn_monitor: 1,
     spawn_monitor: 3, struct: 1, struct: 2, struct!: 1, struct!: 2, throw: 1, tl: 1, trunc: 1,
     tuple_size: 1, update_in: 3]], lexical_tracker: nil, line: 2, macro_aliases: [], macros: [Mex:
     [mex: 1], "IEx.Helpers": [b: 1, h: 1, import_file: 1, import_file: 2, import_file_if_available:
     1, import_if_available: 1, import_if_available: 2, s: 1, t: 1], Kernel: [!: 1, &&: 2, ..: 2, <>:
     2, @: 1, alias!: 1, and: 2, binding: 0, binding: 1, def: 1, def: 2, defdelegate: 2,
     defexception: 1, defimpl: 2, defimpl: 3, defmacro: 1, defmacro: 2, defmacrop: 1, defmacrop: 2,
     defmodule: 2, defoverridable: 1, defp: 1, defp: 2, defprotocol: 2, defstruct: 1, destructure: 2,
     get_and_update_in: 2, if: 2, in: 2, is_nil: 1, match?: 2, or: 2, pop_in: 1, put_in: 2, raise: 1,
     raise: 2, reraise: 2, reraise: 3, sigil_C: 2, sigil_D: 2, sigil_N: 2, sigil_R: 2, sigil_S: 2,
     sigil_T: 2, sigil_W: 2, sigil_c: 2, sigil_r: 2, sigil_s: 2, sigil_w: 2, to_char_list: 1,
     to_charlist: 1, to_string: 1, unless: 2, update_in: 2, use: 1, use: 2, var!: 1, var!: 2, |>: 2,
     ||: 2]], module: nil, requires: [IEx.Helpers, Kernel, Kernel.Typespec, Mex], vars: []})
     

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122. good macros are invisible
     

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123. CJUMZ&MJYJS.FUB
     

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124. !JBNWFSZ
     Questions?
     

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