|> Stream.map(fn stream -> process_book(stream) end)

    |> Stream.map(fn stream -> extract_book(stream) end)

  defp process_book(stream) do

  defp extract_book(stream) do

    |> Stream.take(50)

    |> Stream.take(10)

    {{:title, title}, &parse_author/1}

    {{:title, String.trim(title)}, &parse_author/1}

    {{:author, name}, &identity/1}

    {{:author, String.trim(name)},
     skip_until(
       fn line -> String.starts_with?(line, "*** START OF") end,
       skip_lines(
         6,
         keep_until(fn line -> String.starts_with?(line, "End of") end)
       )
     )}

  defp identity(line) do
    {line, &identity/1}

  defp skip_until(predicate, next) do
    fn l ->
      if predicate.(l) do
        {nil, next}
      else
        {nil, skip_until(predicate, next)}
      end
    end
  end
  defp skip_lines(n, next) do
    fn _ ->
      if n == 0 do
        {nil, next}
      else
        {nil, skip_lines(n - 1, next)}
      end
    end
  end
  defp keep_until(predicate) do
    fn line ->
      if predicate.(line) do
        {nil, nil}
      else
        {{:line, line}, keep_until(predicate)}
      end
    end