The faster Clojure version

gistfile1.clj

(defn foo [x]
  (cond
    (instance? Integer x) "Integer"
    (instance? String  x) "String"
    (instance? Boolean x) "Boolean"))

(defn transient-foo [n] 
  (loop [cnt n col (transient [])]
    (if (= cnt 0) (persistent! col)
    (recur (dec cnt) 
      (reduce #(conj! %1 (foo %2)) col ["foo" 23 true])))))

(time (prn (count (transient-foo 1000000))))