mv.clj

(def mv-limit 20)

(def ^:dynamic *mv-arr*)

(def ^:dynamic *values-expected* 1)

(defn values [& vals]
  (when (thread-bound? #'*values-expected*)
    (dotimes [i (set! *values-expected*
                      (min *values-expected* (count vals)))]
      (aset *mv-arr* i (nth vals i))))
  (first vals))

(defn make-mv-bindings [bindings val1#]
  (->> (iterate inc 1)
       (take (count bindings))
       (map (fn [i]
              `(when (< ~i *values-expected* mv-limit)
                 (aget *mv-arr* ~i))))
       (cons val1#)
       (interleave bindings)))

(defmacro mv-bind [bindings expr & body]
  (let [val1# (gensym)]
    `(binding [*mv-arr*          (if (thread-bound? #'*mv-arr*)
                                   *mv-arr*
                                   (make-array Object mv-limit))
               *values-expected* ~(count bindings)]
       (let [~val1# ~expr
             ~@(make-mv-bindings bindings val1#)]
         ~@body))))

(defn polar [x y]
  [(Math/sqrt (+ (* x x) (* y y))) (Math/atan (/ y x))])

(defn polar-mv [x y]
  (values (Math/sqrt (+ (* x x) (* y y))) (Math/atan (/ y x))))

(time
 (dotimes [i 1e5]
   (let [[r theta] (polar 3 4)])))
;; "Elapsed time: 70.3533 msecs"

(time
 (dotimes [i 1e5]
   (mv-bind [r theta] (polar-mv 3 4))))
;; "Elapsed time: 5894.5376 msecs"