gistfile1.clj

(defmacro with-defaults [defaults definition]
  (let [function-name (first definition)
        arguments (second definition)
        argument-subset (vec (nthrest arguments (count defaults)))
        body (rest (rest definition))]
  `(defn ~function-name
     (~argument-subset
        (~function-name ~@(reverse (concat argument-subset defaults))))
     (~arguments
       ~@definition))))

(with-defaults [1] (show-args [a b] (str a ", " b)))
(show-args 2) ; => 1, 2
(show-args 3 4) ; => 3, 4