Programmer Passport: Elixir

Unquoting, Quoting, and defmacro

Let’s take a moment to recap. Elixir programs are made up of ASTs. These trees have the representation of all Elixir code. Building the AST doesn’t happen all at once, though. Each program is compiled with several different steps. The following figure tells the story.

After a program is loaded, Elixir translates the program into an initial AST in a step called parsing. Then, Elixir applies all macros to the AST in a step called macro expansion. Only then is the program turned into its final executable form.

Because Elixir is a language built mostly in itself, the macro expansion step is important. Let’s look at ...