(defn next-triangle [triangle]
  (let [triangle (vec (map (fn[row-string] (str " " row-string)) triangle))
        triangle (assoc triangle (count triangle) 
                   (nth (iterate (fn[row] (str row "\u25B2\u00A0")) "") (+ 1 (count triangle))))]
    triangle))

(defn print-triangle [triangle]
 (doall (map println triangle))
 (println))

(doall (map print-triangle (take 10 (iterate next-triangle []))))