gistfile1.ex

defmodule Mix.Tasks.Doctest do
  use Mix.Task

  @shortdoc "Run the doctests for one or more files"

  # Just for testing....
  defmodule Wombat do
    @moduledoc """
        iex> 1
        1
        iex> 2
        5
    """
  end

  def run(args) do
#    { opts, files } = OptionParser.parse(args)

    :application.start(:elixir)
    :application.start(:ex_unit)
    test_methods = Enum.map ExUnit.DocTest.__doctests__(Wombat, []), fn { name, test } ->
      {:def,[],[{name,[],[[do: [{:_,[],nil}]]]},[do: test]]}  
    end
    body = [{:use,[],[{:__aliases__,[],[:ExUnit,:Case]},[async: true]]} | test_methods ]
    mod = {:defmodule,[],[{:__aliases__,[],[:Mix, :Tasks, :Doctest, :InternalTests]},
             [do: {:__block__,[], body}]]}
    Code.eval_quoted(mod)
    ExUnit.configure([])
    ExUnit.run
  end 
end

The failure you are getting is probably coming from this on line 22: [[do: [{:_,[],nil}]]. It basically says your function is defined like: def name(do: _), do: test, you probably want this instead: {:def,[],[{name,[],[{:_,[],nil}]},[do: test]]}