Flatten in elixir without library functions

flatten.ex

defmodule MyList do

  def flatten([]) do
    []
  end

  def flatten(value, []) when is_integer(value) do
    value
  end

  def flatten([head | []], enumerates) when is_list(enumerates) do
    [head | flatten(enumerates)]
  end

  def flatten([head | tail]) when is_integer(head) and is_list(tail) do
    [head | flatten(tail)]
  end

  def flatten([head | tail], enumerate) when is_integer(head) and is_integer(tail) and is_list(enumerate) do
    [ head, tail | flatten(enumerate)]
  end

  def flatten([head | tail], enumerate) when is_integer(head) and is_list(tail) and is_list(enumerate) do
    [ head | flatten(tail, enumerate)]
  end

  def flatten([head | []]) when is_list(head) do
    flatten(head)
  end

  def flatten([head | tail]) when is_list(head) and is_list(tail) do
    flatten(head, tail)
  end
end