def caesar([], _), do: []
    def caesar([head | tail], shift) do
        [cypher(head, shift) | caesar(tail, shift)]
    end

    defp cypher(a, shift) when a in ?a..?z and a != 32 do
        97+rem((a-97+shift), 26)
    end
    defp cypher( _, _) do
        ' '
    end