lol.ex

defmodule Test do
  if __ENV__.file != "nofile" do
    @original File.read!(__ENV__.file)
  end

  @doc false
  def unquote(:"$handle_undefined_function")(function, args) do
    arg_def = Enum.map(1..Enum.count(args)//1, fn i -> {:"_arg_#{i}", [], nil} end)
    {:defmodule, meta, [aliases, [{:do, {:__block__, [], ast}}]]} = Code.string_to_quoted!(@original)
    ast = Enum.reduce(ast, [], fn
      {:def, meta, [{{:unquote, [line: line], [:"$handle_undefined_function"]}, [line: _], [{:function, [line: _], nil}, {:args, [line: _], nil}]}, body]}, acc ->
        new = {:def, [line: line], [{function, [line: line], arg_def}, [do: :ok]]}
        [{:def, meta, [{{:unquote, [line: line], [:"$handle_undefined_function"]}, [line: line], [{:function, [line: line], nil}, {:args, [line: line], nil}]}, body]}, new | acc]
      {:if, meta, [{:!=, [line: line], [{{:., [line: line], [{:__ENV__, [line: line], nil}, :file]}, [no_parens: true, line: line], []}, "nofile"]}, [do: {:@, _, [{:original, _, [{{:., _, [{:__aliases__, _, [:File]}, :read!]}, _, [{{:., _, [{:__ENV__, _, nil}, :file]}, [no_parens: true, line: 3], []}]}]}]}]]}, acc ->
        [{:@, meta, [{:original, meta, [@original]}]} | acc]
      {name, meta, ast}, acc ->
        [{name, meta, ast} | acc]
    end)
    |> Enum.reverse
    {:defmodule, meta, [aliases, [{:do, {:__block__, [], ast}}]]}
    |> Code.compile_quoted()
    |> Enum.at(0)
    |> elem(0)
    |> apply(function, args)
  end
end