Clojure Zipper Breadth First Search

bfs.clj

(defn breadth-first-search [z]
  (letfn [(zip-children [loc]
            (when-let [first-child (zip/down loc)]
              (take-while (comp not nil?)
                (iterate zip/right first-child))))])
  (loop [ret []
         queue (conj clojure.lang.PersistentQueue/EMPTY z)]
    (if (seq queue)
      (let [[node children] ((juxt zip/node zip-children) (peek queue))]
        (recur (conj ret node) (into (pop queue) children)))
      ret)))