A brief introduction to Elixir metaprogramming.

1. Metaprogramming in Elixir
A brief introduction

2. What will be about?
macros
quote and unquote
DSLs a.k.a. __using__

3. Rules regarding macros
MACRO RULE #1
DON'T WRITE MACROS
MACRO RULE #2
USE MACROS GRATUITOUSLY

4. What are macros?
A code that writes code

5. Where are macros?
Elixir itself is primarily built with macros
if
unless
cond
def defmodule
assert

6. How do macros work?

7. https://github.com/elixir-lang/elixir/blob/master/lib/elixir/lib/kernel.ex

11. Macro expanding

12. What can macros do?

13. Why to use macros?
Extending the
language to
your needs
Boilerplate
removal

14. ASTs

15. quote
iex(1)> quote do: 1 + 2
{:+, [context: Elixir, import: Kernel], [1, 2]}
Always an atom or another tuple
Metadata
The arguments for the function call

16. unquote
iex(2)> Macro.to_string {
...(2)> :div,
...(2)> [context: Elixir, import: Kernel],
...(2)> [10, 2]
...(2)> }
"div(10, 2)"
iex(1)> quote do: div(10, 2)
{
:div,
[context: Elixir, import: Kernel],
[10, 2]
}

18. __using__

20. Custom type

21. DB migration

22. Model

23. Operations

24. KamilLelonek / exnumerator

25. Learning materials
http://bit.ly/elixir-metaprogramming
http://bit.ly/elixir-macros

26. https://github.com/KamilLelonek/exnumerator
https://blog.lelonek.me/
http://woumedia.com/
https://twitter.com/KamilLelonek