Gain insights into metaprogramming in Elixir. Delve into macros and discover how to elevate your coding skills, creating powerful libraries with concise, efficient code.

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Get introduced to the concept of metaprogramming. Learn how to level up your programming skills by discovering the full potential of the macro system in Elixir. Understand the ins and outs of metaprogramming at a fundamental level and write incredible libraries by doing more with less code.

Metaprogramming in Elixir

Understanding the AST is essential as you get into advanced metaprogramming. Once we uncover the nuances, we’ll find that Elixir code is much closer to the AST than we might have imagined. 

Understanding ASTs will change the way we think about solving problems and drive our macro design decisions in the future. After reviewing the finer details of the AST, we’ll be ready to begin the metaprogramming exercises. 

# The structure of the AST
Every expression we write in Elixir breaks down to a three-element tuple in the AST. We often rely on this uniform breakdown when pattern matching arguments in macros.

Since we know that an expression like `5 + 2` turns into the tuple `{:+, [...], [5, 2]}`, we pattern matched directly against the AST to determine the meaning of each calculation. 

Let’s quote a couple more complex expressions to see how entire Elixir programs are structured in the AST.

Try the command `quote do: (5 * 2) - 1 + 7` in the terminal given below:



Let's try another example.
Execute the following lines of code in the `iex` terminal provided above.


quote do
  defmodule MyModule do
    def hello, do: "World"
  end
end

From the output, we can see that a stacking tuple is produced from each quoted expression. The result of this example shows how a simple AST represents an entire Elixir module.

All along, the code we've written in Elixir is represented by this simple uniform structure. Understanding this structure just requires a few simple rules. 

All Elixir code is represented as a series of three-element tuples with the following format:
- The first element is an atom denoting the function call, or another tuple, representing a nested node in the AST.

- The second element represents metadata about the expression.

- The third element is a list of arguments for the function call

The output of the above program is given for reference:
``` elixir
iex(1)> quote do
...(1)>   defmodule MyModule do
...(1)>     def hello, do: "World"
...(1)>   end
...(1)> end
# Output:
# {:defmodule, [context: Elixir, import: Kernel],
# [
#   {:__aliases__, [alias: false], [:MyModule]},
#   [
#     do: {:def, [context: Elixir, import: Kernel],
#     [{:hello, [context: Elixir], Elixir}, [do: "World"]]}
#  ]
# ]}
```


Learn about the Abstract Syntax Tree (AST) in detail.

Introduction

The Language of Macros

Extending Elixir with Metaprogramming

Advanced Compile-Time Code Generation

Code Generation from Git API

How to Test Macros

Create an HTML Domain-Specific Language

With Great Power Comes Great Responsibility (and Fun!)

The Abstract Syntax Tree

The structure of the AST