Implementation of combinations and permutations in Elixir

combinatorics.ex

defmodule Combinatorics do
  def combinations(_, 0), do: [[]]
  def combinations([], _), do: []
  def combinations([head | rest], n) do
    (for item <- combinations(rest, n - 1), do: [head | item]) ++ combinations(rest, n)
  end

  def permutations([]), do: [[]]
  def permutations(list) do
    for h <- list, t <- permutations(list -- [h]), do: [h | t]
  end
  def permutations(list, n) do
    list |> combinations(n) |> Enum.map(&permutations/1) |> Enum.concat()
  end
end