Naive implementation of multi-arity defun in CL.

defun-multi.lisp

(defmacro defun-multi (name &body clauses)
  (let ((vars-sym (gensym "VARS")))
    `(defun ,name (&rest ,vars-sym)
       (ecase (length ,vars-sym)
         ,@(loop
              for (vars . body) in clauses
              collect `(,(length vars)
                         (destructuring-bind ,vars ,vars-sym ,@body))))) ))