Calculating permutations in Elixir

permutations.ex

defmodule Permutations do
  def permutate([]), do: [[]]
  def permutate(list) do
    for n <- list,
        p <- permutate(list -- [n]),
        do: [n | p]
  end
end

permutations_test.exs

defmodule PermutationsTest do
  use ExUnit.Case

  test "permutates a list" do
    assert Permutations.permutate([]) == [[]]
    assert Permutations.permutate([1]) == [[1]]
    assert Permutations.permutate([1, 2]) == [[1, 2], [2, 1]]
    assert Permutations.permutate([1, 2, 3]) == [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]
  end
end