A handy `with` macro

gistfile1.ex

defmodule With do
  @doc """
  Provides a shortcut for multiple function invocations on the same module.

  Example:

      x = [1,2,3,4]
      with List do
          @append [x, @reverse x]
      end
      # => [1,2,3,4,4,3,2,1]

      # Without `with` macro we would have to write
      x = [1,2,3,4]
      List.append [x, List.reverse x]
  """
  defmacro with(ref, do_block) do
    block = Orddict.get do_block, :do
    replace_at(block, ref)
  end

  defp replace_at({ :@, line, [{fun, _, fun_args}] }, ref) do
    {{:".", line, [ref, fun]}, line, replace_at(fun_args, ref)}
  end

  defp replace_at(tuple, ref) when is_tuple(tuple) do
    list_to_tuple(replace_at(tuple_to_list(tuple), ref))
  end

  defp replace_at(list, ref) when is_list(list) do
    lc item in list, do: replace_at(item, ref)
  end

  defp replace_at(other, _) do
    other
  end
end