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

# The trial terminal
Use this terminal to test and execute the commands provided in the lesson:

# Generating less code while maintaining the DSL

Our `Html` module is clear and concise, but we had to generate over a hundred macros to make it work. Wouldn’t it be nice to generate less code but still maintain our expressive DSL where all tags can be used as macro calls? Let’s make it happen.



The idea of maintaining the DSL without generating all HTML macros sounds impossible, but step back and remember that Elixir provides full AST access. For example, open up an `iex` prompt and quote a few arbitrary HTML DSL expressions, and let’s look at the results. Do not load `Html` module since we are just quoting raw expressions outside the context of our library for this example by executing the following commands:
``` elixir
iex> ast = quote do
...>   div do
...>     h1 do   
...>       text "hello"
...>     end
...>   end
...> end
# Output: {:div, [], [[do: {:h1, [], [[do: {:text, [], ["Hello"]}]]}]]}
```

It looks pretty simple, right? We received the AST representation of the macro DSL in the form we first saw in the lesson [The Abstract Syntax Tree](https://www.educative.io/courses/metaprogramming-elixir/the-abstract-syntax-tree) of Chapter 2. We can see our macro calls are neatly nested in a series of three-element tuples. Now imagine instead of generating all HTML tags as macros, we could instead walk the AST, piece by piece, and convert the AST nodes like `{:div, [] [[do: ...]]}` into `tag :div do ...` macro calls. Elixir comes with built-in functions to help us do this.

## The `prewalk` and `postwalk` functions
Elixir contains the `Macro.prewalk/2` and `Macro.postwalk/2` functions that allow us to walk an AST depth-first or breadth-first. Let’s use `IO.inspect` to see what happens if we walk the AST for our quoted expression that we bound to the `ast` variable above:

>__Note__: The following commands will only work if the complete AST is defined using the commands given above.



Learn to maintain the expressive DSL by using much less code.

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!)

Generating Less Code by Walking the AST

The trial terminal

Generating less code while maintaining the DSL