Stumped with functional breadth-first tree traversal in Clojure?

Question

Say I have a tree defined as per the recommendation in this post, although it\'s a vector in my case, which hopefully shouldn\'t matter (they\'re vectors in Programming Clojure

Answer 1

Since apparently there is still no breadth-first solution posted, here is a simple algorithm, implemented first eagerly, and then transformed to be lazy:

(defn bfs-eager [tree]
  (loop [ret [], queue (conj clojure.lang.PersistentQueue/EMPTY tree)]
    (if (seq queue)
      (let [[node & children] (peek queue)]
        (recur (conj ret node) (into (pop queue) children)))
      ret)))

(defn bfs-lazy [tree]
  ((fn step [queue]
     (lazy-seq
      (when (seq queue)
        (let [[node & children] (peek queue)]
          (cons node
                (step (into (pop queue) children)))))))
   (conj clojure.lang.PersistentQueue/EMPTY tree)))