How to get the full generated code of a module using Elixir macros

Question

Below is the router module for a sample Phoenix application. I would like to see the full code of the module after macros inject functions.

I tried things like Macro.to_string (Macro.expand (Code.string_to_quoted! File.read!("web/router.ex")), __ENV__) but it doesn't fully expand the macros. How could I recursively expand every macro, i.e. pipeline, plug, scope, pipe_through and get.

Thanks

defmodule HelloPhoenix.Router do use HelloPhoenix.Web, :router pipeline :browser do plug :accepts, ["html"] plug :fetch_session plug :fetch_flash plug :protect_from_forgery plug :put_secure_browser_headers end pipeline :api do plug :accepts, ["json"] end scope "/", HelloPhoenix do pipe_through :browser # Use the default browser stack get "/", PageController, :index end end

Chris Meyer · Accepted Answer · 2016-03-16 14:28:01Z

This bit of code will decompile a beam file back to erlang. I haven't run it against a plug-based module, so I don't know how nasty the result will be, but this gives you the final result for any module.

 def disassemble(beam_file) do beam_file = String.to_char_list(beam_file) {:ok, {_, [{:abstract_code, {_, ac}}]}} = :beam_lib.chunks(beam_file, [:abstract_code]) :io.fwrite('~s~n', [:erl_prettypr.format(:erl_syntax.form_list(ac))]) end

original source, and more info: http://erlang.org/doc/man/beam_lib.html

Note that this method takes the file path of [module].beam

Too bad we can't have elixir code but as I can read erlang better than elixir it's okay for me :) Thank you

Patrick Oscity · Accepted Answer · 2016-03-15 19:27:55Z

6

As you have correctly observed, you need to use Macro.expand/1 recursively to truly expand all macro levels. There is a built-in facility to achieve this: Macro.prewalk/2. This should get you started:

ast |> Macro.prewalk(&Macro.expand(&1, __ENV__)) |> Macro.to_string |> IO.puts

answered Mar 15, 2016 at 19:27

Patrick Oscity

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2 Comments

lud Over a year ago

I can't make it work. I also found a package called Mex that can't seem to print the full code either. But thanks anyway, I'll tinker a bit more

Patrick Oscity Over a year ago

Oh it seems inspecting modules is not as straightforward, sorry. If you want to get a quick and dirty solution you can try to manually inject the inspection code into the module itself, so that your __ENV__ is within the module. Can't check right now but you might have some success with that.

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