gistfile1.txt

(defn level-order [f tree]
  (loop [to-do [tree]]
    (if (empty? to-do)
      :done
      (do (dorun (map (comp f :value) to-do))
          (recur (mapcat (fn [{:keys [left right]}] (remove nil? [left right]))
                         to-do))))))

(level-order println
             {:value 1
              :left {:value 2
                     :left {:value 4}
                     :right {:value 5}}
              :right {:value 3
                      :left {:value 6}
                      :right {:value 7}}})