An Elixir Shell helper for previewing macroexpansion.

Displays different levels of macroexpansion side-by-side, along with where and why the expansion fails (if it does).

Install by adding a dev dependency on mex:

1. Add mex to your list of dependencies in mix.exs:

   def deps do [{:mex, "~> 0.0.1", only: :dev}] end

2. Ensure mex is started before your application:

   def application do [applications: [:mex]] end

Then import and configure it in your project's .iex.exs:

import Mex
Mex.set_width 160   # (optional) default width is 80 chars

mex do
  expr  # <-- expression you'd like expanded.
end

By default, mex will display 4 columns: no_expansion, Macro.expand_once, Macro.expand, and Mex.expand_all.

You can display fewer columns (1-3) by passing an argument to mex before the block:

iex(0)> import Mex
iex(2)> mex 3 do
          expression_to_macro_expand
        end
 
<will display 3 columns>

You can also display only a single expander by instead supplying one of :none, :once, :expand, :all as argument, or use the function Mex.pp_compare if you want to supply your own expanders.