Don't Write Macros - But Do Learn How They Work

September 7, 2017 @ ElixirConf

Transcript

2. why macros?
3. defmodule MyModule do def my_function do ... end end
4. defmodule MyModule do def my_function do ... end end
5. defmodule MyModule do def my_function do ... end end
6. why not macros?
7. The first rule of macro club is don't write macros. ~ Stuart Halloway ~
8. Code is read many more times than it is written, which means that the ultimate cost of code is in its reading. ~ Sandi Metz ~
9. if
10. if 1 + 2 == 3, do: "this", else: "that"
11. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that")
12. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that")
13. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that")
14. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that")
15. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that")
16. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that")
17. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that") if(1 + 2 == 3, [do: "this", else: "that"])
18. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that") if(1 + 2 == 3, [do: "this", else: "that"])
19. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that") if(1 + 2 == 3, [do: "this", else: "that"])
20. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that") if(1 + 2 == 3, [do: "this", else: "that"])
21. if 1 + 2 == 3, do: "this", else: "that" if(1 + 2 == 3, do: "this", else: "that") if(1 + 2 == 3, [do: "this", else: "that"])
22. if(1 + 2 == 3, [do: "this", else: "that"])
23. if(1 + 2 == 3, [do: "this", else: "that"])
24. 1 + 2 == 3
25. 1 + 2 == 3 (1 + 2) == 3
26. 1 + 2 == 3 (1 + 2) == 3
27. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3
28. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3
29. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3
30. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3)
31. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3)
32. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3)
33. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3)
34. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3)
35. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3)
36. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3) Kernel.==(+(1, 2), 3)
37. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3) Kernel.==(+(1, 2), 3)
38. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3) Kernel.==(+(1, 2), 3)
39. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3) Kernel.==(+(1, 2), 3) Kernel.==(Kernel.+(1, 2), 3)
40. 1 + 2 == 3 (1 + 2) == 3 +(1, 2) == 3 ==(+(1, 2), 3) Kernel.==(+(1, 2), 3) Kernel.==(Kernel.+(1, 2), 3)
41. Kernel.==(Kernel.+(1, 2), 3)
42. Kernel.==(Kernel.+(1, 2), 3) if(1 + 2 == 3, [{:do, "this"}, {:else, "that"}])
43. Kernel.==(Kernel.+(1, 2), 3) if(1 + 2 == 3, [{:do, "this"}, {:else, "that"}])
44. if(Kernel.==(Kernel.+(1, 2), 3), [{:do, "this"}, {:else, "that"}])
45. if(Kernel.==(Kernel.+(1, 2), 3), [{:do, "this"}, {:else, "that"}])
46. if(Kernel.==(Kernel.+(1, 2), 3), [{:do, "this"}, {:else, "that"}]) Macro.if(Kernel.==(Kernel.+(1, 2), 3), [{:do, "this"}, {:else, "that"}])
47. if(Kernel.==(Kernel.+(1, 2), 3), [{:do, "this"}, {:else, "that"}]) Macro.if(Kernel.==(Kernel.+(1, 2), 3), [{:do, "this"}, {:else, "that"}])
48. Macro.if(Kernel.==(Kernel.+(1, 2), 3), [{:do, "this"}, {:else, "that"}])
49. Macro.if(Kernel.==(Kernel.+(1, 2), 3), [{:do, "this"}, {:else, "that"}]) if 1 + 2 == 3, do: "this", else: "that"
51. Elixir compiler
52. Steps of Elixir Compiler Read file Credit Michał Muskała
53. Steps of Elixir Compiler Read file Tokenize Credit Michał Muskała
54. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Credit Michał Muskała
55. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Credit Michał Muskała
56. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Credit Michał Muskała
57. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST Credit Michał Muskała
58. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST (now Erlang compiler takes over) Credit Michał Muskała
59. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST (now Erlang compiler takes over) Compile Erlang AST to Core AST Credit Michał Muskała
60. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST (now Erlang compiler takes over) Compile Erlang AST to Core AST
 Core Optimizations & True Inlining Credit Michał Muskała
61. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST (now Erlang compiler takes over) Compile Erlang AST to Core AST
 Core Optimizations & True Inlining Compile Pattern Matching Credit Michał Muskała
62. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST (now Erlang compiler takes over) Compile Erlang AST to Core AST
 Core Optimizations & True Inlining Compile Pattern Matching (now we have "kernel Erlang") Credit Michał Muskała
63. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST (now Erlang compiler takes over) Compile Erlang AST to Core AST
 Core Optimizations & True Inlining Compile Pattern Matching (now we have "kernel Erlang") Run Kernel Optimizations Credit Michał Muskała
64. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST (now Erlang compiler takes over) Compile Erlang AST to Core AST
 Core Optimizations & True Inlining Compile Pattern Matching (now we have "kernel Erlang") Run Kernel Optimizations Generate Assembly Credit Michał Muskała
65. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST (now Erlang compiler takes over) Compile Erlang AST to Core AST
 Core Optimizations & True Inlining Compile Pattern Matching (now we have "kernel Erlang") Run Kernel Optimizations Generate Assembly Optimize Assembly Credit Michał Muskała
66. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST (now Erlang compiler takes over) Compile Erlang AST to Core AST
 Core Optimizations & True Inlining Compile Pattern Matching (now we have "kernel Erlang") Run Kernel Optimizations Generate Assembly Optimize Assembly Generate Bytecode Credit Michał Muskała
67. Steps of Elixir Compiler Read file Tokenize Parse (builds AST) Expand Macros Apply Rewrite Rules Lower Elixir AST to Erlang AST (now Erlang compiler takes over) Compile Erlang AST to Core AST
 Core Optimizations & True Inlining Compile Pattern Matching (now we have "kernel Erlang") Run Kernel Optimizations Generate Assembly Optimize Assembly Generate Bytecode Write .beam file Credit Michał Muskała
69. My version
70. Step 1: Take code
71. Step 1: Take code Step 2: Build Abstract Syntax Tree
72. Step 1: Take code Step 2: Build Abstract Syntax Tree Step 3: ?????
73. Step 1: Take code Step 2: Build Abstract Syntax Tree Step 3: ????? Step 4: Profit!
74. Step 1: Take code Step 2: Build Abstract Syntax Tree Step 3: ????? Step 4: Profit! The Beam!
75. Abstract Syntax Tree (AST)
77. Quote Literals:
78. atoms
 :foo Quote Literals:
79. atoms integers
 :foo 42 Quote Literals:
80. atoms integers floats
 :foo 42 13.1 Quote Literals:
81. atoms integers floats strings
 :foo 42 13.1 "hello" Quote Literals:
82. atoms integers floats strings lists
 :foo 42 13.1 "hello" [1, 2, 3] Quote Literals:
83. atoms integers floats strings lists 2-element
 tuples
 :foo 42 13.1 "hello" [1, 2, 3] {"hello", :world} Quote Literals:
84. atoms integers floats strings lists 2-element
 tuples
 :foo 42 13.1 "hello" [1, 2, 3] {"hello", :world} Quote Literals: 3-element Tuples:
85. atoms integers floats strings lists 2-element
 tuples
 :foo 42 13.1 "hello" [1, 2, 3] {"hello", :world} variable {name, meta, context} Quote Literals: 3-element Tuples:
86. atoms integers floats strings lists 2-element
 tuples
 :foo 42 13.1 "hello" [1, 2, 3] {"hello", :world} variable {name, meta, context} {:foo, [], Elixir} Quote Literals: 3-element Tuples:
87. atoms integers floats strings lists 2-element
 tuples
 :foo 42 13.1 "hello" [1, 2, 3] {"hello", :world} variable {name, meta, context} {:foo, [], Elixir} call {function, context/meta, args} Quote Literals: 3-element Tuples:
88. atoms integers floats strings lists 2-element
 tuples
 :foo 42 13.1 "hello" [1, 2, 3] {"hello", :world} variable {name, meta, context} {:foo, [], Elixir} call {function, context/meta, args} Quote Literals: 3-element Tuples:
89. AST call example
90. 1 + 2
91. 1 + 2 Kernel.+(1, 2)
92. 1 + 2 Kernel.+(1, 2) {:+, [context: Elixir, import: Kernel], [1, 2]}
93. 1 + 2 Kernel.+(1, 2) {:+, [context: Elixir, import: Kernel], [1, 2]}
94. 1 + 2 Kernel.+(1, 2) {:+, [context: Elixir, import: Kernel], [1, 2]}
95. 1 + 2 Kernel.+(1, 2) {:+, [context: Elixir, import: Kernel], [1, 2]}
96. 1 + 2 Kernel.+(1, 2) {:+, [context: Elixir, import: Kernel], [1, 2]}
97. quote unquote Macro.to_string defmacro
98. quote
99. iex(1)>
100. iex(1)> quote do: 1 + 2
101. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)>
102. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> quote do: :atom
103. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> quote do: :atom :atom iex(3)>
104. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> quote do: :atom :atom iex(3)> quote do: [1, 2, 3]
105. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> quote do: :atom :atom iex(3)> quote do: [1, 2, 3] [1, 2, 3] iex(4)>
106. unquote
107. iex(1)>
108. iex(1)> quote do: 1 + 2
109. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)>
110. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> foo = 2
111. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> foo = 2 2 iex(3)>
112. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> foo = 2 2 iex(3)> quote do: 1 + foo
113. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> foo = 2 2 iex(3)> quote do: 1 + foo {:+, [context: Elixir, import: Kernel], [1, {:foo, [], Elixir}]} iex(4)>
114. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> foo = 2 2 iex(3)> quote do: 1 + foo {:+, [context: Elixir, import: Kernel], [1, {:foo, [], Elixir}]} iex(4)>
115. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> foo = 2 2 iex(3)> quote do: 1 + foo {:+, [context: Elixir, import: Kernel], [1, {:foo, [], Elixir}]} iex(4)>
116. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> foo = 2 2 iex(3)> quote do: 1 + foo {:+, [context: Elixir, import: Kernel], [1, {:foo, [], Elixir}]} iex(4)> quote do: 1 + unquote(foo)
117. iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> foo = 2 2 iex(3)> quote do: 1 + foo {:+, [context: Elixir, import: Kernel], [1, {:foo, [], Elixir}]} iex(4)> quote do: 1 + unquote(foo) {:+, [context: Elixir, import: Kernel], [1, 2]} iex(5)>
118. iex(1)>
119. iex(1)> foo = 2
120. iex(1)> foo = 2 2 iex(2)>
121. iex(1)> foo = 2 2 iex(2)> "the value is foo"
122. iex(1)> foo = 2 2 iex(2)> "the value is foo" "the value is foo" iex(3)>
123. iex(1)> foo = 2 2 iex(2)> "the value is foo" "the value is foo" iex(3)> "the value is #{foo}"
124. iex(1)> foo = 2 2 iex(2)> "the value is foo" "the value is foo" iex(3)> "the value is #{foo}"
125. iex(1)> foo = 2 2 iex(2)> "the value is foo" "the value is foo" iex(3)> "the value is #{foo}"
126. iex(1)> foo = 2 2 iex(2)> "the value is foo" "the value is foo" iex(3)> "the value is #{foo}" "the value is 2" iex(4)>
127. Macro.to_string
128. iex(1)>
129. iex(1)> math_problem = quote do: 1 + 2
130. iex(1)> math_problem = quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)>
131. iex(1)> math_problem = quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> Macro.to_string(math_problem)
132. iex(1)> math_problem = quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]} iex(2)> Macro.to_string(math_problem) "1 + 2" iex(3)>
133. iex(1)>
134. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that"
135. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that"
136. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that"
137. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [context: Elixir, import: Kernel], [{:==, [context: Elixir, import: Kernel], [{:+, [context: Elixir, import: Kernel], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)>
138. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [context: Elixir, import: Kernel], [{:==, [context: Elixir, import: Kernel], [{:+, [context: Elixir, import: Kernel], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)>
139. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [...], [{:==, [...], [{:+, [...], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)>
140. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [...], [{:==, [...], [{:+, [...], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)>
141. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [...], [{:==, [...], [{:+, [...], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)>
142. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [...], [{:==, [...], [{:+, [...], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)>
143. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [context: Elixir, import: Kernel], [{:==, [context: Elixir, import: Kernel], [{:+, [context: Elixir, import: Kernel], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)>
144. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [context: Elixir, import: Kernel], [{:==, [context: Elixir, import: Kernel], [{:+, [context: Elixir, import: Kernel], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)> Macro.to_string(foo)
145. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [context: Elixir, import: Kernel], [{:==, [context: Elixir, import: Kernel], [{:+, [context: Elixir, import: Kernel], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)> Macro.to_string(foo) "if(1 + 2 == 3) do\n \"this\"\nelse\n \"that\"\nend"
146. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [context: Elixir, import: Kernel], [{:==, [context: Elixir, import: Kernel], [{:+, [context: Elixir, import: Kernel], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)> Macro.to_string(foo) |> IO.puts
147. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [context: Elixir, import: Kernel], [{:==, [context: Elixir, import: Kernel], [{:+, [context: Elixir, import: Kernel], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)> Macro.to_string(foo) |> IO.puts if(1 + 2 == 3) do "this" else "that" end :ok
148. iex(1)> foo = quote do: if 1 + 2 == 3, do: "this", else: "that" {:if, [context: Elixir, import: Kernel], [{:==, [context: Elixir, import: Kernel], [{:+, [context: Elixir, import: Kernel], [1, 2]}, 3]}, [do: "this", else: "that"]]} iex(2)> Macro.to_string(foo) |> IO.puts if(1 + 2 == 3) do "this" else "that" end :ok
149. More AST Examples
150. {1, 2, 3}
151. {1, 2, 3} {:{}, [], [1, 2, 3]}
152. {1, 2, 3} {:{}, [], [1, 2, 3]}
153. {1, 2, 3} {:{}, [], [1, 2, 3]}
154. {1, 2, 3} {:{}, [], [1, 2, 3]}
155. %{name: "Steve", age: 12}
156. %{name: "Steve", age: 12} {:%{}, [] [name: "Steve", age: 12]}
157. IO.puts("hello")
158. IO.puts("hello") {{:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"]}
159. IO.puts("hello") { {:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"] }
160. IO.puts("hello") { {:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"] }
161. IO.puts("hello") { {:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"] }
162. IO.puts("hello") { {:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"] }
163. IO.puts("hello") { {:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"] }
164. IO.puts("hello") { {:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"] }
165. IO.puts("hello") { {:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"] }
166. IO.puts("hello") { { :., [], [{:__aliases__, [alias: false], [:IO]}, :puts] }, [], ["hello"] }
167. IO.puts("hello") { { :., [], [{:__aliases__, [alias: false], [:IO]}, :puts] }, [], ["hello"] }
171. defmacro unquote(:.)(left, right), do: error!([left, right])
172. defmacro unquote(:.)(left, right), do: error!([left, right])
173. defmacro unquote(:.)(left, right), do: error!([left, right]) ... defmacrop error!(args) do quote do _ = unquote(args) message = "Elixir's special forms are expanded by the compiler and must not be invoked directly" :erlang.error(RuntimeError.exception(message)) end end
174. defmacro unquote(:.)(left, right), do: error!([left, right]) ... defmacrop error!(args) do quote do _ = unquote(args) message = "Elixir's special forms are expanded by the compiler and must not be invoked directly" :erlang.error(RuntimeError.exception(message)) end end
175. defmacro unquote(:.)(left, right), do: error!([left, right]) ... defmacrop error!(args) do quote do _ = unquote(args) message = "Elixir's special forms are expanded by the compiler and must not be invoked directly" :erlang.error(RuntimeError.exception(message)) end end
176. IO.puts("hello") { { :., [], [{:__aliases__, [alias: false], [:IO]}, :puts] }, [], ["hello"] }
177. IO.puts("hello") { { :., [], [{:__aliases__, [alias: false], [:IO]}, :puts] }, [], ["hello"] }
178. IO.puts("hello") { { :., [], [{:__aliases__, [alias: false], [:IO]}, :puts] }, [], ["hello"] }
179. IO.puts("hello") { { :., [], [{:__aliases__, [alias: false], [:IO]}, :puts] }, [], ["hello"] }
180. IO.puts("hello") { { :., [], [{:__aliases__, [alias: false], [:IO]}, :puts] }, [], ["hello"] }
181. IO.puts("hello") { { :., [], [{:__aliases__, [alias: false], [:IO]}, :puts] }, [], ["hello"] }
182. IO.puts("hello") { { :., [], [{:__aliases__, [alias: false], [:IO]}, :puts] }, [], ["hello"] }
183. {:__aliases__, [alias: false], [:ModuleName]}
184. {:__aliases__, [alias: false], [:ModuleName]}
185. {:__aliases__, [alias: false], [:ModuleName]}
186. {:__aliases__, [alias: false], [:ModuleName]}
187. {:__aliases__, [alias: false], [:ModuleName]}
188. {:__aliases__, [alias: false], [:ModuleName]}
189. {:__aliases__, [alias: false], [:ModuleName]} ModuleName
190. IO.puts("hello") { {:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"] }
191. IO.puts("hello") { {:., [], [IO, :puts]}, [], ["hello"] }
192. {:., [], [IO, :puts]}
193. {:., [], [IO, :puts]} IO . puts
194. {:., [], [IO, :puts]} IO . puts
195. {:., [], [IO, :puts]} IO . puts
196. {:., [], [IO, :puts]} IO . puts
197. {:., [], [IO, :puts]} IO.puts
198. IO.puts("hello") { {:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"] }
199. IO.puts("hello") { IO.puts, [], ["hello"] }
200. IO.puts("hello") { {:., [], [{:__aliases__, [alias: false], [:IO]}, :puts]}, [], ["hello"] }
201. defmacro
202. defmodule MyMacros do end
203. defmodule MyMacros do defmacro my_if do end end
204. defmodule MyMacros do defmacro my_if do end end
205. defmodule MyMacros do defmacro my_if do end end
206. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do end end
207. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do end end
208. iex(1)> quote do: 1 + 2 == 3
209. iex(1)> quote do: 1 + 2 == 3 {:==, [context: Elixir, import: Kernel], [{:+, [context: Elixir, import: Kernel], [1, 2]}, 3]} iex(2)>
210. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do end end
211. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do end end
212. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do end end
213. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do case condition do true -> do_clause _ -> else_clause end end end
214. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do quote do case condition do true -> do_clause _ -> else_clause end end end end
215. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do quote do case condition do true -> do_clause _ -> else_clause end end end end
216. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do quote do case condition do true -> do_clause _ -> else_clause end end end end
217. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do quote do case condition do true -> do_clause _ -> else_clause end end end end
218. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do quote do case unquote(condition) do true -> do_clause _ -> else_clause end end end end
219. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do quote do case unquote(condition) do true -> do_clause _ -> else_clause end end end end
220. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do quote do case unquote(condition) do true -> unquote(do_clause) _ -> unquote(else_clause) end end end end
221. iex(1)>
222. iex(1)> require MyMacros
223. iex(1)> require MyMacros MyMacros iex(2)>
224. iex(1)> require MyMacros MyMacros iex(2)> MyMacros.my_if 1 + 2 == 3, do: "this", else: "that"
225. iex(1)> require MyMacros MyMacros iex(2)> MyMacros.my_if 1 + 2 == 3, do: "this", else: "that" "this" iex(3)>
226. iex(1)> require MyMacros MyMacros iex(2)> MyMacros.my_if 1 + 2 == 3, do: "this", else: "that" "this" iex(3)> MyMacros.my_if 1 + 2 == 10, do: "this", else: "that"
227. iex(1)> require MyMacros MyMacros iex(2)> MyMacros.my_if 1 + 2 == 3, do: "this", else: "that" "this" iex(3)> MyMacros.my_if 1 + 2 == 10, do: "this", else: "that" "that" iex(4)>
228. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do quote do case unquote(condition) do true -> unquote(do_clause) _ -> unquote(else_clause) end end end end
229. defmodule MyMacros do defmacro my_if(condition, do: do_clause, else: else_clause) do quote do case unquote(condition) do true -> unquote(do_clause) _ -> unquote(else_clause) end end end end
230. defmodule MyFunctions do def my_if(condition, do: do_clause, else: else_clause) do case condition do true -> do_clause _ -> else_clause end end end
231. defmodule MyFunctions do def my_if(condition, do: do_clause, else: else_clause) do case condition do true -> do_clause _ -> else_clause end end end
232. iex(1)>
233. iex(1)> require MyFunctions
234. iex(1)> require MyFunctions MyFunctions iex(2)>
235. iex(1)> require MyFunctions MyFunctions iex(2)> MyFunctions.my_if 1 + 2 == 3, do: "this", else: "that"
236. iex(1)> require MyFunctions MyFunctions iex(2)> MyFunctions.my_if 1 + 2 == 3, do: "this", else: "that" "this" iex(3)>
237. iex(1)> require MyFunctions MyFunctions iex(2)> MyFunctions.my_if 1 + 2 == 3, do: "this", else: "that" "this" iex(3)> MyFunctions.my_if 1 + 2 == 10, do: "this", else: "that"
238. iex(1)> require MyFunctions MyFunctions iex(2)> MyFunctions.my_if 1 + 2 == 3, do: "this", else: "that" "this" iex(3)> MyFunctions.my_if 1 + 2 == 10, do: "this", else: "that" "that" iex(4)>
239. iex(1)> require MyFunctions MyFunctions iex(2)>
240. iex(1)> require MyFunctions MyFunctions iex(2)> MyFunctions.my_if 1 + 2 == 3, do: IO.puts("this"), else: IO.puts("that")
241. iex(1)> require MyFunctions MyFunctions iex(2)> MyFunctions.my_if 1 + 2 == 3, do: IO.puts("this"), else: IO.puts("that") this that :ok iex(3)>
242. iex(1)> require MyFunctions MyFunctions iex(2)> MyFunctions.my_if 1 + 2 == 3, do: IO.puts("this"), else: IO.puts("that") this that :ok iex(3)> MyFunctions.my_if 1 + 2 == 10, do: IO.puts("this"), else: IO.puts("that")
243. iex(1)> require MyFunctions MyFunctions iex(2)> MyFunctions.my_if 1 + 2 == 3, do: IO.puts("this"), else: IO.puts("that") this that :ok iex(3)> MyFunctions.my_if 1 + 2 == 10, do: IO.puts("this"), else: IO.puts("that") this that :ok
244. iex(1)>
245. iex(1)> require MyMacros MyMacros iex(2)>
246. iex(1)> require MyMacros MyMacros iex(2)> MyMacros.my_if 1 + 2 == 3, do: IO.puts("this"), else: IO.puts("that")
247. iex(1)> require MyMacros MyMacros iex(2)> MyMacros.my_if 1 + 2 == 3, do: IO.puts("this"), else: IO.puts("that") this :ok iex(3)>
248. iex(1)> require MyMacros MyMacros iex(2)> MyMacros.my_if 1 + 2 == 3, do: IO.puts("this"), else: IO.puts("that") this :ok iex(3)> MyMacros.my_if 1 + 2 == 10, do: IO.puts("this"), else: IO.puts("that")
249. iex(1)> require MyMacros MyMacros iex(2)> MyMacros.my_if 1 + 2 == 3, do: IO.puts("this"), else: IO.puts("that") this :ok iex(3)> MyMacros.my_if 1 + 2 == 10, do: IO.puts("this"), else: IO.puts("that") that :ok
250. one more thing...
251. pattern matching
252. defmodule MyMacros do defmacro my_macro({:function, meta, [arg1, arg2]}) do quote do ... end end end
253. defmodule MyMacros do defmacro my_macro({:function, meta, [arg1, arg2]}) do quote do ... end end end
254. defmodule MyMacros do defmacro pretty_math({:+, _meta, [left, right]} = ast) do quote do IO.puts """ #{unquote(left)} + #{unquote(right)} --- #{unquote(ast)} """ end end end
255. defmodule MyMacros do defmacro pretty_math({:+, _meta, [left, right]} = ast) do quote do IO.puts """ #{unquote(left)} + #{unquote(right)} --- #{unquote(ast)} """ end end end
256. defmodule MyMacros do defmacro pretty_math({:+, _meta, [left, right]} = ast) do quote do IO.puts """ #{unquote(left)} + #{unquote(right)} --- #{unquote(ast)} """ end end end
257. defmodule MyMacros do defmacro pretty_math({:+, _meta, [left, right]} = ast) do quote do IO.puts """ #{unquote(left)} + #{unquote(right)} --- #{unquote(ast)} """ end end end
258. defmodule MyMacros do defmacro pretty_math({:+, _meta, [left, right]} = ast) do quote do IO.puts """ #{unquote(left)} + #{unquote(right)} --- #{unquote(ast)} """ end end end
259. iex(1)>
260. iex(1)> require MyMacros
261. iex(1)> require MyMacros MyMacros iex(2)>
262. iex(1)> require MyMacros MyMacros iex(2)> MyMacros.pretty_math 1 + 2
263. iex(1)> require MyMacros MyMacros iex(2)> MyMacros.pretty_math 1 + 2 1 + 2 --- 3 :ok iex(3)>
264. bit.ly/elixir_macros ELIXIR MACRO RESOURCES @jessejanderson FOLLOW ME