gistfile1.clj

(ns joc
  (:use [clojure.test]))

(defn rpn-orig
  ([tokens] (rpn-orig tokens []))
  ([[top & tail] stack]
     (lazy-seq
      (if top
	(if (fn? top)
	  (let [l (peek stack)
		s (pop stack)
		r (peek s)]
	    (rpn-orig tail (conj (pop s) (top r l))))
	  (rpn-orig tail (conj stack top)))
	stack))))

(defn rpn
  ([[top & tail] & stack]
     (lazy-seq
      (if top
	(if (fn? top)
	  (apply rpn tail (top (first stack) (second stack))
		 (drop 2 stack))
	  (apply rpn tail top stack))
       stack))))
  
(deftest test-rpm
  (are [x y] (= x y)
       [3] (rpn [1 2 +])
       [100000] (joc/rpn (vec (take 99999 (repeat +)))
			 (vec (take 100000 (repeat 1))))))

user> (time (apply joc/rpn (vec (take 99999 (repeat +)))
       (take 100000 (repeat 1))))

"Elapsed time: 52.788637 msecs"
(100000)

user> (time (joc/rpn-orig (vec (take 99999 (repeat +)))
          (vec (take 100000 (repeat 1)))))

"Elapsed time: 104.770117 msecs"
(100000)