Quicksort in Elixir

quicksort.ex

defmodule Quicksort do
  @spec sort([any()], :asc | :desc) :: [any()]
  def sort(values, direction \\ :asc) do
    sorted = sort(values)

    if direction == :asc do
      sorted
    else
      Enum.reverse(sorted)
    end
  end

  # Sort the list in ascending order
  defp sort([], _dir), do: []
  defp sort([x], _dir), do: [x]

  defp sort([p | rest], dir) do
    # Partition `rest` in a single pass 
    {lesser, greater} =
      Enum.reduce(rest, {[p], []}, fn x, {left, right} ->
        if x < p do
          {[x | left], right}
        else
          {left, [x | right]}
        end
      end)

    Enum.concat(sort(left), sort(right))
  end
end