Encode a list using Elixir

encode_list.exs

# I wrote this after watching Dave Thomas review his implementation
# in this presentation: https://www.youtube.com/watch?v=5hDVftaPQwY
 
defmodule MyList do
 
  def encode(list), do: _encode(list, [])
  
  defp _encode([     a, a | tail], acc), do: _encode([  {a, 2} | tail], acc)
  defp _encode([{a, n}, a | tail], acc), do: _encode([{a, n+1} | tail], acc)
  defp _encode([{a, n}, b | tail], acc), do: _encode([       b | tail], [{a, n} | acc])
  defp _encode([     a, b | tail], acc), do: _encode([       b | tail], [     a | acc])
  defp _encode([               a], acc), do: _encode([               ], [     a | acc])
  defp _encode([                ], acc), do: Enum.reverse acc
  
end
 
IO.inspect [8, 8, 8, 8, 8, 8, 7, 5, 5, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0] |> MyList.encode
# prints: [{8, 6}, 7, {5, 3}, {0, 9}]