parens.ex

defmodule Parens do
  def generate(n) do
    n
    |> generate_trees()
    |> Enum.map(&IO.iodata_to_binary/1)
  end

  defp generate_trees(0), do: []
  defp generate_trees(1), do: [["()"]]
  defp generate_trees(n) do
    Enum.flat_map(generate_tree(n - 1), fn
      ["()" | _rest] = list ->
        [["()", list], ["(", list, ")"]]
      list ->
        [["()", list], ["(", list, ")"], [list, "()"]]
    end)
  end
end