I like the keyword args support in Common Lisp. So, when I learned that clojure didn't support keyword args in the base language, I was a bit disappointed. But, with clojure's support for destructuring and macros, it should be easy to build keyword args … right?
Rich Hickey posted a simple example on the clojure mailing list, which I adapted slightly to my taste:
(defmacro defun [sym args & body] (let [[pargs [_ & kargs]] (split-with (fn [x] (not (= x '&key))) args) gkeys (gensym "gkeys__") letk (fn [k] (let [[nm val] (if (vector? k) k [k]) kname (keyword (name nm))] `(~nm (or (~gkeys ~kname) ~val))))] `(defn ~sym [~@pargs & k#] (let [~gkeys (apply hash-map k#) ~@(apply concat (map letk kargs))] ~@body))))
(defun foo [a b &key c [d 5]] [a b c d]) user> (foo 1 2 :c 10) [1 2 10 5]