my_list.exs

#
# my solution to ListsAndRecursion-6 of Programming Elixir 1.6
#
defmodule MyList do
  def flatten([]) do
    []
  end

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

  def flatten([head | tail]) do
    [head | flatten(tail)]
  end
end