Macro examples

Let's go through some more in-depth examples of using macros to accomplish some pretty cool things, things that are generally fairly difficult to accomplish in other languages.

Debugging and tracing

We'll start with a debugging/tracer module that will enable us to automatically trace the methods of our library.

Note

Of course, this is highly unnecessary since the Erlang VM itself is capable of adding this functionality for us without requiring anything from the developer.

As part of this example, we're going to dive into use and __using__. use as it turns out, is a relatively simple function that invokes the __using__ macro of the module passed. This, in turn, injects the code of the __using__ macro.

For example, let's say we've defined a basic module, UsingTest, as the following code:

defmodule UsingTest do
  defmacro __using__(_opts) do
    quote do
      IO.puts "I'm the __using__/1 of #{unquote(__MODULE__)}"
    end
  end
end

If we then define another, very simple module, say...