IPersistentStack ref: http://qiita.com/iku000888/items/4b65a0b030195d19e111

file0.cljs

;; conj to a list
(conj '(1 2 3 4) 5) => (5 1 2 3 4)

;; conj to a vector
(conj [1 2 3 4] 5) => [1 2 3 4 5]

file1.cljs

(-> [1 2 3 4]
    (conj 5)
    peek) =>5

(-> '(1 2 3 4)
    (conj 5)
    peek) => 5

file2.cljs

;; popping from a vector
(-> [1 2 3 4]
    (conj 5)
    pop) => [1 2 3 4]

;; popping from a list
(-> '(1 2 3 4)
    (conj 5)
    pop) => (1 2 3 4)

file3.cljs

(time
 (last [1 2 3 4 5 6 7 8 9]))
;; "Elapsed time: 0.171368 msecs"


(time
 (peek [1 2 3 4 5 6 7 8 9]))
;; "Elapsed time: 0.066708 msecs"