gistfile1.ex

defmodule ListPairs do
  defp _find([], _, acc), do: acc

  defp _find([h|t], target_sum, acc) do
    accepted_pairs = Enum.filter_map t, &(&1 + h == target_sum), &({h, &1})
    _find(t, target_sum, acc ++ accepted_pairs)
  end

  def find(list, target_sum) do
    _find(list, target_sum, [])
  end
end

IO.puts inspect ListPairs.find([1, 2, 8, 3, 4, 7], 10)