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Intro to elixir metaprogramming
- 1. Intro to Elixir metaprogramming FirstKyiv Elixir meetup, June 23, 2016
- 2. Hello! I am AntonMishchuk from Lviv ▧ Ruby Dev at Matic (and we are hiring) ▧ Fan of Elixir programming language ▧ ESpec creator & maintainer ▧ GitHub: antonmi 2
- 3. Elixir is Erlangwith pretty syntax and metaprogramming! What is Elixir? 3
- 4. ▧ Elixir AST ▧Quote and unquote ▧ Macroses ▧ DSL ▧ Introspection What will be about 4
- 5. Why metaprogramming ▧ Extendinglanguage ▧ Boilerplate removing ▧ Creating DSL 5
- 6. Ecto.Schema Elixir metaprogramming inthe wild Source code 6
- 7. Phoenix.Router Elixir metaprogramming inthe wild Source code 7
- 8. ESpec.Let Elixir metaprogramming inthe wild Source code 8
- 9. Initial code parsing Elixircode Initial AST Expansion Expanded AST Byte-code generation Byte-code Compilation process Magic is here! 9
- 10. Compile-time metaprogramming ▧ Codewill not be redefined ▧ Static code analysis still works ▧ No performance penalty 10
- 11. Elixir AST. Quoting ‘quote’macro gets the representation of any expression. 11
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- 13. ▧ The firstelement is an atom identifying the operation or another tuple in the same representation ▧ The second element is a keyword list containing metadata, like numbers and contexts ▧ The third element is either a list of arguments for the function call or an atom. When this element is an atom, it means the tuple represents a variable Elixir AST - 3 element tuple 13
- 14. Elixir AST stringrepresentation ‘Macro.to_string’ converts the given expression to a binary 14
- 15. Elixir AST evaluation ‘Code.eval_string’and ‘Code.eval_quoted’ 15
- 16. Elixir AST. Unquoting Unquotingis a mechanism to inject code chunks into quoted expressions. i.e. inject one AST fragment into another Let’s try an example: 16
- 17. Elixir AST. Unquoting Tryingto evaluate ‘final_expr’ I want to build AST which adds 1 + 2 17
- 18. Elixir AST. Unquoting ‘unquote’helps to inject AST fragment 18
- 19. Magic functions -Macros ▧ Macro (which stands for "macroinstruction") is a programmable pattern which translates a certain sequence of input into a preset sequence of output ▧ Macros receive the input AST and must produce the output AST ▧ The compiler will then simply replace the macro call with the AST returned from that macro ▧ Works only at compile time 19
- 20. ▧ ‘defmodule’, ‘defmacro’,‘def’, defstruct ▧ ‘require’, ‘import’, ‘use’ ▧ ‘If’, ‘unless’, ‘cond’ ▧ etc, etc Macros are everywhere 87% of Elixir code written on Elixir 20
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- 22. Macros. Example The resultis expect. Nothing special. Because we see completely compiled code in the iex console 22
- 23. Macros. Example Remember, macrosreceive quoted expression and return them Let’s do what compiler did step by step 23
- 24. Macros. Dynamic functiondefinition example 24
- 25. Macros. ‘require’ and‘import’ We should tell the compiler which module should be compiled before we can use it. 25
- 26. ‘use’ macro The simplestway to bring external functionality into the current lexical scope 26
- 27. ‘Use’ for DSL ‘UseEcto.Migration’ ‘Ecto.Migration.__using__’ 27
- 28. ‘Use’ for DSL ‘useGenServer’ 28
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- 30. ‘Use’ for DSL ‘useESpec’ 30
- 31.
- 32. OMG! How tohandle all the stuff? ▧ What function/macro I can use in current scope? ▧ Where does this function/macro come from? 32
- 33. Elixir introspection ▧ __ENV__: Returns a Macro.ENV struct containing current environment information ▧ __MODULE__ : Returns the current module name as an atom ▧ __DIR__ : Returns the current directory ▧ __CALLER__ : Returns the caller’s environment information as a Macro. ENV struct 33
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- 35. And don’t forgetabout help ‘h IEx.Helpers.b’ 35
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- 37. With great powercomes great responsibility! Thank you! 37