rlm@0: ;; Various Operators on Pure Functions
rlm@0: ;;
rlm@0: ;; Open source Liscence and all that
rlm@0: (ns 
rlm@0:     rlm.function-utils
rlm@0:   "Collection of Operators on Pure Functions"
rlm@1:   {:author "Robert McIntyre"})
rlm@0: 
rlm@0: (def void ::void)
rlm@0: 
rlm@0: (defn mix 
rlm@0:   "Takes any number of mathematically equal functions with
rlm@0:    possibly different run-times and returns a function that
rlm@0:    runs each in a separate thread, returns the result from
rlm@0:    the first thread which finishes, and cancels the other threads."
rlm@0:   {:author "Robert McIntyre"}
rlm@0:   ([& functions]
rlm@0:      (fn [& args]
rlm@0:        (let [result (promise)
rlm@0: 	     futures (doall (for [fun functions]
rlm@0: 			      (future (deliver result (apply fun args)))))
rlm@0: 	     answer @result]
rlm@0: 	 (dorun (map future-cancel futures))
rlm@0: 	 answer))))
rlm@0: 
rlm@1: ;; (defn mix-threads
rlm@1: ;;   " Takes any number of pure functions that take the same arguments and
rlm@1: ;;    compute the same value and returns a function that runs each in a separate
rlm@1: ;;    thread, returns the result from the first thread which finshes, and cancels 
rlm@1: ;;    the other threads. Explicitly uses nasty Threads.
rlm@0: 
rlm@1: ;;    For example: 
rlm@1: ;;    (do
rlm@1: ;;    (defn fun1 [] (Thread/sleep 5000) 5)
rlm@1: ;;    (defn fun2 [] (Thread/sleep 700000) 5)
rlm@1: ;;    (time ((mix fun1 fun2))))
rlm@0:    
rlm@1: ;;    Returns: 
rlm@1: ;;     | Elapsed time: 5000.66214 msecs
rlm@1: ;;    5"
rlm@1: ;;   [& functions]
rlm@1: ;;   (fn [& args]
rlm@1: ;;     (let [result (prof :create-atom (atom void))
rlm@1: ;; 	  threads
rlm@1: ;; 	   (prof :create-threads (map 
rlm@1: ;; 	   (fn [fun] 
rlm@1: ;; 	     (Thread. 
rlm@1: ;; 	      (fn [] 
rlm@1: ;; 		(try (let [answer (apply fun args)]
rlm@1: ;; 		       (reset! result answer))
rlm@1: ;; 		     (catch Exception _ nil)))))
rlm@1: ;; 	   functions))]
rlm@0:       
rlm@1: ;;       (prof :start-threads (dorun (map #(.start %) threads)))
rlm@1: ;;       (prof :loop (loop []
rlm@1: ;; 	(if (=  (deref result) void)
rlm@1: ;; 	  (recur)
rlm@1: ;; 	  (do (prof :kill-threads (dorun (map #(.stop %) threads)))
rlm@1: ;; 	      (prof :return (deref result)))))))))
rlm@0: 
rlm@0: (defmacro defmix
rlm@0:   " Defines a function from any number of pure functions that take the same 
rlm@0:    arguments and compute the same value which:
rlm@0: 
rlm@0:    Runs each in a separate thread.
rlm@0:    Returns the result from the first thread which finshes.
rlm@0:    Cancels the other threads.
rlm@0:            
rlm@0:    Use this whenever you want to combine two pure functions that
rlm@0:    compute the same thing, but use different algorithms with different
rlm@0:    run times for various inputs.
rlm@0: 
rlm@0:    For example: 
rlm@0:      (do
rlm@0:      (defn fun1 [] (Thread/sleep 5000) 5)
rlm@0:      (defn fun2 [] (Thread/sleep 700000) 5)
rlm@0:      (defmix fun3 \"combination of fun1 and fun2\" fun1 fun2)
rlm@0:      (time (fun3))
rlm@0:    
rlm@0:    Returns: 
rlm@0:      | Elapsed time: 5000.66214 msecs
rlm@0:      5"
rlm@0: 
rlm@0: {:arglists '([name doc-string? functions*])}
rlm@0: 
rlm@0:   [name & functions]
rlm@0:   (let [doc-string (if (string? (first functions)) (first functions) "")
rlm@0: 	functions (if (string? (first functions)) (rest functions) functions)
rlm@0: 	arglists (:arglists (meta (resolve (eval `(quote ~(first functions))))))
rlm@1: 	name (with-meta name
rlm@1:                (assoc (meta name) :arglists `(quote ~arglists)
rlm@1:                       :doc doc-string))]   
rlm@0:     `(def ~name (mix ~@functions))))
rlm@0: 
rlm@0: (defn runonce
rlm@0:   "Decorator.  returns a function which will run only once. Inspired
rlm@0:    by Halloway's version from lancet."
rlm@0:   {:author "Robert McIntyre"}
rlm@0:   [function]
rlm@0:   (let [sentinel (Object.) 
rlm@0: 	result (atom sentinel)]
rlm@0:     (fn [& args]
rlm@0:        (locking sentinel
rlm@0: 	 (if (= @result sentinel) 
rlm@0: 	   (reset! result (apply function args)) 
rlm@0: 	    @result)))))
rlm@0: