letfn.clj

(defmacro letfn- [fn-bindings & body]
  (let [fn-names (map first fn-bindings)
        fn-gensyms (into {} (for [f fn-names]
                              [f (gensym f)]))
        delayed-bindings (for [f fn-names
                               x [(fn-gensyms f)
                                  `(delay (~f ~@fn-names))]]
                           x)
        forced-bindings (for [[n v] fn-gensyms
                              x [n `(force ~v)]]
                          x)
        fn-bindings (for [form fn-bindings
                          :let [form (if (vector? (second form))
                                       (list (first form) (rest form))
                                       form)]
                          x [(first form)
                             `(fn* ~(vec fn-names)
                                   (let ~(vec delayed-bindings)
                                     (fn ~@(for [f (rest form)
                                                 :let [[args & body] f]]
                                             `(~args (let ~(vec forced-bindings)
                                                       ~@body))))))]]
                      x)]
    `(let ~(reduce into (vec fn-bindings) [delayed-bindings forced-bindings])
       ~@body)))