;; This is based on the dlambda macro presented in "Let Over Lambda" by Doug Hoyte.

(defmacro dlambda (&rest methods)
  (let ((arguments (gensym)))

    `(lambda (&rest, arguments)
       (case (first, arguments), @(mapcar
                                                             (lambda (method))
                                                               `(, (first method))
                                                                 (apply (lambda, @(rest method)), (if (equal t (first method)))
                                                                                                                            arguments
                                                                                                                            `(rest, arguments))
                                                             methods)))))