force

clojure.core

  • (force x)
If x is a Delay, returns the (possibly cached) value of its expression, else returns x

2 Examples top

  • ;; an example for delay using an event-queue
    user> (import  [java.util.concurrent PriorityBlockingQueue])
    java.util.concurrent.PriorityBlockingQueue
    user> (defn create-event-element [delayed-event tme]
      (struct event delayed-event tme))
    #'user/create-event-element
    user> (defn comp-queue [e1 e2]
      (if (< (:time e1) (:time e2))
        true false))
    #'user/comp-queue
    user> (defn update [n]
    	(reset! c n))
    #'user/update
    user> (defn create-event-queue [comp-queue size]
      (new PriorityBlockingQueue size (comp comp-queue)))
    #'user/create-event-queue
    user> (def queue (create-event-queue comp-queue 10))
    #'user/queue
    user> (def elements (take 10 (repeatedly 
    			      (fn[](create-event-element 
    				    (delay (update (rand-int 20)))
    				    (rand))))))
    #'user/elements
    user> (def c (atom 0))
    #'user/c
    user> @c
    0
    user> (doseq [e elements]
    	     (.add queue e))
    nil
    user> (dotimes [_ 10]
    	       (let [e (.poll queue)]
    		    (println "c=" @c)
    		    (print "time=" (:time e) ":")
    		    (println (force (:object e)))))
    c= 0
    time= 0.07805244345581108 :19
    c= 19
    time= 0.24297414417455565 :6
    c= 6
    time= 0.24427040715816817 :0
    c= 0
    time= 0.24938478920862384 :17
    c= 17
    time= 0.33612588239752494 :6
    c= 6
    time= 0.5148481493716295 :5
    c= 5
    time= 0.5823642080700586 :7
    c= 7
    time= 0.7674970100941858 :4
    c= 4
    time= 0.9206272921555505 :14
    c= 14
    time= 0.9958255204018474 :4
    nil
    user> @c
    4
    user> (def elements (take 10 (repeatedly 
    			      (fn[](create-event-element 
    				    (delay (update (rand-int 20)))
    				    (rand))))))
    #'user/elements
    ;; if we check 'element', delay objects will be evaluated. The below is
    ;; this example. Please compare the above with the below.
    user> elements  
    ({:object #<Delay@37a63e06: 16>, :time 0.48566816399656854} {:object #<Delay@3321875: 19>, :time 0.9374202154797486} {:object #<Delay@4de3aaf6: 17>, :time 0.3271116626875401} {:object #<Delay@1ded246d: 15>, :time 0.8843712542267577} {:object #<Delay@3bf27f74: 10>, :time 0.86383171974926} {:object #<Delay@2d8db76b: 14>, :time 0.2120086056700251} {:object #<Delay@3304e92a: 5>, :time 0.9406336968276247} {:object #<Delay@767de91: 0>, :time 0.2150071400135528} {:object #<Delay@34450563: 7>, :time 0.7520042839572664} {:object #<Delay@1f64c164: 1>, :time 0.6264819751284463})
    ;; The object of the last elements is #<Delay@1f64c164: 1>. Therefore,
    ;; This indicates the atom 'c' has already updated.
    user> @c  
    1 
    user> (doseq [e elements]
    	     (.add queue e))
    nil
    ;; 'atom c' has never been updated because it has already
    ;; been evaluated.
    user> (dotimes [_ 10]
    	       (let [e (.poll queue)]
    		    (println "c=" @c)
    		    (print "time=" (:time e) ":")
    		    (println (force (:object e)))))
    c= 1
    time= 0.2120086056700251 :14
    c= 1
    time= 0.2150071400135528 :0
    c= 1
    time= 0.3271116626875401 :17
    c= 1
    time= 0.48566816399656854 :16
    c= 1
    time= 0.6264819751284463 :1
    c= 1
    time= 0.7520042839572664 :7
    c= 1
    time= 0.86383171974926 :10
    c= 1
    time= 0.8843712542267577 :15
    c= 1
    time= 0.9374202154797486 :19
    c= 1
    time= 0.9406336968276247 :5
    nil
    user> 
  • ;; the tarai benchmark comparing non-lazy version with lazy-version
    (defn tarai [x y z]
      (if (<= (x) (y))
          (y)
          (recur (fn [] (tarai (fn [] (- (x) 1)) y z))
                 (fn [] (tarai (fn [] (- (y) 1)) z x))
                 (fn [] (tarai (fn [] (- (z) 1)) x y)))))
    
    (defn tarai-d [x y z]
      (if (<= (force x) (force y))
          (force y)
          (recur (delay (tarai-d (- (force x) 1) y z))
                   (delay (tarai-d (- (force y) 1) z x))
                   (delay (tarai-d (- (force z) 1) x y)))))
    
    user> (dotimes [_ 10] (time (tarai (fn [] 192) (fn [] 96) (fn [] 0))))
    "Elapsed time: 139.660729 msecs"
    "Elapsed time: 132.493587 msecs"
    "Elapsed time: 135.867772 msecs"
    "Elapsed time: 132.924774 msecs"
    "Elapsed time: 137.491084 msecs"
    "Elapsed time: 134.72752 msecs"
    "Elapsed time: 132.969652 msecs"
    "Elapsed time: 135.795754 msecs"
    "Elapsed time: 134.261724 msecs"
    "Elapsed time: 138.059968 msecs"
    
    nil
    user> (dotimes [_ 10 ]  (time (tarai-d 192 96 0)))
    "Elapsed time: 3.181795 msecs"
    "Elapsed time: 2.960096 msecs"
    "Elapsed time: 3.000855 msecs"
    "Elapsed time: 3.140536 msecs"
    "Elapsed time: 3.658821 msecs"
    "Elapsed time: 3.319659 msecs"
    "Elapsed time: 2.9182 msecs"
    "Elapsed time: 3.125442 msecs"
    "Elapsed time: 2.944342 msecs"
    "Elapsed time: 2.951613 msecs"
    nil
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See Also top

  • 0
    clojure.core/delay

    Takes a body of expressions and yields a Delay object that will inv

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Plus_12x12 Minus_12x12 Source clojure/core.clj:696 top

(defn force
  "If x is a Delay, returns the (possibly cached) value of its expression, else returns x"
  {:added "1.0"
   :static true}
  [x] (. clojure.lang.Delay (force x)))
Vars in clojure.core/force:
Used in 0 other vars

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