Metaprogramming in ElixirA brief introduction

What will be about?

macros quote and unquote DSLs a.k.a. __using__

Rules regarding macrosMACRO RULE #1

DON'T WRITE MACROS

MACRO RULE #2

USE MACROS GRATUITOUSLY

What are macros?A code that writes code

Where are macros?

Elixir itself is primarily built with macros

ifunless

cond

def defmodule

assert

How do macros work?

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

Macro expanding

What can macros do?

Why to use macros?

Extending the language to your needs

Boilerplate removal

ASTs

quote

iex(1)> quote do: 1 + 2 {:+, [context: Elixir, import: Kernel], [1, 2]}

Always an atom or another tupleMetadata

The arguments for the function call

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] }

__using__

Custom type

DB migration

Model

Operations

KamilLelonek / exnumerator

Learning materials

http://bit.ly/elixir-metaprogramminghttp://bit.ly/elixir-macros

https://github.com/KamilLelonek/exnumerator

https://blog.lelonek.me/

http://woumedia.com/

https://twitter.com/KamilLelonek