Guacamole method used by the command ingredient.

        :param ctx:
            The guacamole context object. Context provides access to all
            features of guacamole. The argparse ingredient adds the ``args``
            attribute to it. That attribute contains the result of parsing
            command line arguments.
        :returns:
            The return code of the command. Guacamole translates ``None`` to a
            successful exit status (return code zero).

def invoked(self, ctx):
        """
        Guacamole method used by the command ingredient.

        :param ctx:
            The guacamole context object. Context provides access to all
            features of guacamole. The argparse ingredient adds the ``args``
            attribute to it. That attribute contains the result of parsing
            command line arguments.
        :returns:
            The return code of the command. Guacamole translates ``None`` to a
            successful exit status (return code zero).
        """
        print("{} + {} = {}".format(
            ctx.args.x,
            ctx.args.y,
            ctx.args.x + ctx.args.y))