mattmitchell.clj

;; this should let you do something like
;;
;; (defn foobar
;;   [x y z]
;;   (with-defaults
;;     [x (even? x) 1881
;;      y (odd? y) 823]
;;     (+ x y z)))
;;

(defmacro with-defaults
  [triples & body]
  (let [lettings
          (mapcat
            (fn [[arg-name validity default]]
              (list arg-name (list 'if validity arg-name default)))
            (partition 3 triples))]
    `(let [~@lettings] ~@body)))