iex> MapSet.new(1..32) |> Enum.to_list
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,
 23, 24, 25, 26, 27, 28, 29, 30, 31, 32]

iex> MapSet.new(1..33) |> Enum.to_list
[11, 26, 15, 20, 17, 25, 13, 8, 7, 1, 32, 3, 6, 2, 33, 10, 9, 19, 14, 5, 18, 31,
 22, 29, 21, 27, 24, 30, 23, 28, 16, 4, 12]

Aquí esta laimplementación en Elixir 1.3

def new(enumerable) do
  map =
    enumerable
    |> Enum.to_list
    |> do_new([])

  %MapSet{map: map}
end

defp do_new([], acc) do
  acc
  |> :lists.reverse
  |> :maps.from_list
end

defp do_new([item | rest], acc) do
  do_new(rest, [{item, true} | acc])
end

Aunque el orden no importa en unMapSet, pero todavía me pregunto por qué unMapSet se desordena después de 32 elementos?