Elixir in Elixir

Transcript

1. Metaprogramming Programs that Write Programs

2. InElixir Elixir

3. ElixirConf Orlando!

4. How to give the talk

5. 1. Set up the Topic

6. How much?

7. It depends™

8. What is “Elixir”?

9. Basics + STDLIB

10. of Elixir is written in Elixir 78%

11. of Elixir is written in Elixir 78% 87%

12. Compare to Ruby’s 44%

13. Numbers? Meh

14. if

15. def

16. |>

17. Metaprogramming

18. 2. Introductions

19. https://iamvery.com — @iamvery Jay Hayes

20. None
21. None
22. None

23. We’re hiring!

24. 3. Definitions

25. Metaprogramming

26. None
27. None

28. Code generation

29. Definition, plz

30. Metaprogramming

31. programming

32. Work on Data

33. 4 + 2

34. 4 + 2 data

35. 4 + 2 data func

36. +(4, 2)

37. Kernel. ( , ) 4 2 +

38. 4 2 +

39. 4 2 + # => 6

40. Meta…

41. The program is data

42. Programming the Program

43. Code generation

44. 4. Macros & Expressions

45. Macros

46. Macros are everywhere

47. good macros are invisible

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

    end end

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

    end end macros

50. What is the data?

51. What is the data? Program

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

    end end

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

    end end

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

    end end

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

    end end

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

    end end

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

    end end

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

    end end

59. Program macro Program ✨ ✨

60. Program macro Program ✨ ✨

61. Program macro Program ✨ ✨

62. Program macro Program Expression Expression ✨ ✨

63. Quoted expression?

64. Code Expressed as Data

65. {:+, [], [1, 2]}

66. Abstract Syntax Tree

67. / 1 + 2 3

68. / 1 + 2 3 / 1 + 2 3

69. ( ( )) / 1 + 2 3

70. ( ( )) / 1 + 2 3 func

71. ( ( )) / 1 + 2 3 func Args

72. ( ( )) / 1 + 2 3 func Args

73. 1 / ( 2 + 3 )

74. / 1 + 2 3

75. {: , …, [ , {: , …, [ ,

    ]} / 1 + 2 3

76. {func, meta, args}

77. {func, meta, args} +(1, 2)

78. {:+, [], [1, 2]}

79. Back to macros…

80. Macros are Functions

81. Args are quoted

82. Args are quoted

83. (not evaluated)

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

    => true

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

    false end

86. Compile time

87. Expression.match?(:lol > :wat) Expression.match?(:lol = :wat)

88. false true

89. Must return quoted

90. Must return quoted

91. Code generation

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

93. Expression.badmatch # (MatchError)

94. :lol = :wat # (MatchError)

95. Program macro Program Expression Expression ✨ ✨

96. 5. Quoting

97. {:+, [], [1, {:-, [], [2, 3]}]}

98. Quote/2

99. Easier to grok

100. Return AST of Expression

101. Return AST of Expression

102. {func, meta, args}

103. quote do :lol = :wat end

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

105. quote do 1 / (2 + 3) end

106. {:/, [], [1, {:+, [2, 3]}

107. {:/, [], [1, {:+, [2, 3]}

108. ]} {:/, [], [1, {:+, [2, 3]}

109. Why “quote”?

110. Like strings…

111. Sort of…

112. “1+1”

113. eval “1+1”

114. eval “1+1” # => 2

115. quote(do: 1+1)

116. expr = quote(do: 1+1) Code.eval_quoted(expr)

117. expr = quote(do: 1+1) Code.eval_quoted(expr) # => {2, []}

118. Bonus:Syntax✔

119. Recursive

120. Terminal Values

121. Quoted Literals

122. 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]

123. 6. Unquoting

124. Value Injection

125. Unquote/1

126. Strings?

127. Like string interpolation

128. Sort of…

129. Inject value into quoted string

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

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

132. Inject value into quoted Expression

133. num = 42 expr = quote do: 1 + num

     # => {:+, [], [1, {:num, [], :Elixir}]}

134. num = 42 expr = quote do: 1 + num

     # => {:+, [], [1, {:num, [], :Elixir}]} Code.eval_quoted(expr) # ERROR! `num` is undefined

135. num = 42 expr = quote do: 1 + unquote(num)

     # => {:+, [], [1, 42]}

136. num = 42 expr = quote do: 1 + unquote(num)

     # => {:+, [], [1, 42]} Code.eval_quoted(expr) # => {43, []}

137. num = 42 expr = “1 + #{num}” # =>

     “1 + 42” eval expr # => 43

138. Inject value into quoted Expression

139. “It’s already quoted”

140. Expression Injection

141. one = quote do: 1 + 1 # => {:+,

     [], [1, 1]} two = quote do: 2 + 2 # => {:+, [], [2, 2]} sum = quote do: unquote(one) + unquote(two) # => {:+, [], [ # {:+, [], [1, 1]}, # {:+, [], [2, 2]} # ]}

142. Code.eval_quoted(sum) # => {6, []}

143. 7. Write a Macro

144. if

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

146. if(…, do: …, else: …)

147. if(…, [do: …, else: …])

148. if(…, [do: …, else: …]) cond

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

150. Truthy & Falsey

151. false || nil Falsey

152. Anything else Truthy

153. case … do x when x in [false, nil] ->

     … _ -> … end

154. case … do x when x in [false, nil] ->

     … _ -> … end cond

155. case … do x when x in [false, nil] ->

     … _ -> … end cond cases

156. 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

157. 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

158. 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 cases

159. 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

160. 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

161. 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 cases

162. 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

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

164. case do x when x in [false, nil] -> _

     -> end IO.puts(“Pass!”) IO.puts(“Fail.”) foo > 0

165. 8. Wrap Up with Guidance

166. When to macro…

167. #1 Don’t

168. Write functions

169. import String defmacro adds(a, b) do quote do to_integer(unquote(a)) +

     to_integer(unquote(b)) end end

170. import String defmacro adds(a, b) do quote do to_integer(unquote(a)) +

     to_integer(unquote(b)) end end

171. import String def adds(a, b) do to_integer(a) + to_integer(b) end

172. Prefer direct solutions

173. Decision based on args

174. Transformation

175. Less error-prone

176. #2 Constants

177. defmodule Conversions do defmacro seconds_per_minute, do: 60 defmacro minutes_per_hour, do:

     60 end

178. h/t module attrs @second_per_minute

179. #3 DSL

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

     content.” end end end

181. scope “/”, HelloWeb do pipe_through :browser get “/”, PageController, :index

     end

182. #4 Hide details

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

184. #5 Reduce boilerplate

185. Language extension

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

187. :elixir_module.compile(Lolwat, {:def, [context: Elixir, import: Kernel], [{:lol, [context: Elixir], Elixir},

     [do: :wat]]}, [], __ENV__)

188. :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, =~: 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: []})
189. None
190. None

191. 9. Self Promotion

192. bit.ly/ElixirMeta2

193. Questions? @iamvery

194. With love,