Custom Language Constructs
Explore how to build custom language constructs in Elixir by recreating core macros like if and designing new features such as a while loop. Understand the use of macros, AST transformation, and control flow techniques to extend Elixir's capabilities and create flexible, reusable code.
We'll cover the following...
We’ve learned that macros allow us to effectively create our own keywords in the language, but they also allow Elixir to be flexible against future requirements.
For example, instead of waiting for the language to add a parallel for comprehension, we could extend the built-in for macro with a new para macro that spawns processes to run the comprehensions in parallel.
It could look something like this:
If implemented, para would transform the for AST into code that runs the comprehension in parallel. The original code would gain just one natural para invocation while executing the built-in comprehension in an entirely new way.
José, the creator of Elixir, gives us a solid language foundation that we can craft to meet our needs.
Re-creating the if macro
Consider the if macro from our unless example in the lesson Macros: The Building Blocks of Chapter 2. The if macro might appear special, but we know it’s a macro like any other.
Let’s recreate Elixir’s if macro to learn how easy it is to implement features using the building blocks of the language.
Consider the following example:
defmodule ControlFlow do
defmacro my_if(expr, do: if_block), do: if(expr, do: if_block, else: nil)
defmacro my_if(expr, do: if_block, else: else_block) do
quote do
case unquote(expr) do
result when result in [false, nil] -> unquote(else_block)
_ -> unquote(if_block)
end
end
end
endNote: Run the ...