enigma.ex

defmodule Enigma do
  defmacro is_alpha(char) do
    quote do: (unquote(char) >= 65 and unquote(char) <= 90) or (unquote(char) >= 97 and unquote(char) <= 122)
  end

   def break_code([head | tail], offset) when is_alpha(head) do
      [head + offset | break_code(tail, offset)]
   end
   def break_code([head | tail], offset) do
     [head | break_code(tail, offset)]
   end
   def break_code([], _) do
     []
   end
end