flatten array elixir

FlattenArray.ex

  defmodule FlattenArray do
    @doc """
    Accept a list and return the list flattened without nil values.
    ## Examples
    iex> FlattenArray.flatten([1, [2], 3, nil])
    [1,2,3]
    iex> FlattenArray.flatten([nil, nil])
    []
    """

    @spec flatten(list) :: list
    def flatten([]), do: [] # optimization
    def flatten(l), do: flatten([], [], l)

    def flatten(acc, [], []), do: Enum.reverse(acc) # reversing an accumulated list is fast in EVM
    def flatten(acc, queue, []), do: flatten(acc, [], queue) # process queue once element is empty
    def flatten(acc, queue, [nil | t]), do: flatten(acc, queue, t) # skip nil
    def flatten(acc, queue, [[]  | t]), do: flatten(acc, queue, t) # skip empty list
    def flatten(acc, queue, [h   | t]) when is_list(h), do: flatten(acc, [t | queue], h) # push tail into queue, and process element
    def flatten(acc, queue, [h   | t]), do: flatten([h | acc], queue, t) # put element into accumulator
  end