array_flattener.ex

defmodule ArrayFlattener do

  def flatten(list) do
    flatten(list, []) |> :lists.reverse
  end

  def flatten([], acc) do; acc; end
  def flatten([head|rest], acc) when is_list(head) do
    flatten rest, flatten(head, acc)
  end
  def flatten([head|rest], acc) do
    flatten rest, [head|acc]
  end
end

defmodule ArrayFlattenerTest do
  use ExUnit.Case

  test "the truth" do
    assert ArrayFlattener.flatten([[1, 2], 3]) === [1, 2, 3]
  end
end