gistfile1.ex

defmodule MyApp do
  def clean_string(str), do: String.codepoints(str) |> _clean([])

  defp _clean([], result) do
    result
    |> Enum.reverse
    |> to_string
  end

  defp _clean([h | t], result) do
    case is_clean?(h) do
      true ->
        _clean(t, [h | result])
      false ->
        _clean(t, result)
    end
  end

  defp is_clean?(str), do: String.match?(str, ~r/(\s|\w)/)
end

defmodule MyAppTest do
  use ExUnit.Case
  doctest MyApp

  test "the truth" do
    MyApp.clean_string("Th#is! i^s a& di@@rty sen$te#nc@e") ==  "This is a dirty sentence"
  end
end