learning to use zippers..

binary-zipper.clj

(def s {:l {:l {:val 4}
            :r {:val 6}
            :val 10}
        :r {:val 20
            :l {:val 11
                :l {:val 3}
                :r {:val 8}}
            :r {:val 9
                :l {:val 2}
                :r {:val 7}}}
        :val 30})

(def btree (z/zipper (constantly true) #(keep identity [(:l %) (:r %)])
                     (fn [nd [x y & rest]]
                       (if-not rest (assoc nd :l x :r y)
                               (throw (Exception. "Invalid use of make-node in zipper")))) s))
(def inced-btree
  (let [myinc #(when %
                 (clojure.pprint/pprint [% (meta %)])
                 (update-in % [:val] inc))]
    (loop [loc btree]
      (if (z/end? loc) (z/root btree)
          (recur (-> (z/edit loc myinc) z/next))))))