You might be interested in micro-code-revue (not arguing about the
design, but simpler details) as well:
(apply f [x]) can be replaced by (f x)
(not= x nil) can be (almost) replaced by x if you know x cannot be the
value 'false' (sufficient in your case)
(. scanner nextInt) is a somewhat deprecated form. Write it (.nextInt scanner)
(fn [x] (println x)) is just println => you can pass println function "as is"
Try hard avoiding direct recursive function calls like (def f [...]
... (f ...))) => this fills the stack, and the JVM has a stack limited
in size.
Prefer the use of recur (when possible ! => it is in your case)
Side note.
If you were not in a case where you're seeking for the max perf., you
would probably address the problem differently : decompose the problem
in multisteps.
For example, here, you could have a function whose purpose is to
create a sequence of vals from the input:
(defn incoming-ints [in]
(let [sc (java.util.Scanner. in)]
(repeatedly #(.nextInt sc))))
Then you would walk over this sequence while its value is different from 42 :
(doseq [i (incoming-ints System/in) :while (not= i 42)]
(println i))
HTH,
--
Laurent
2011/4/19 Michael Golovanov <[email protected]>:
> Hi everyone
>
> I have the same task implementation on Java and Clojure. Task is very
> simple: User input integers to the console. Program need print inputed
> integers until user input is 42.
> Clojure implementation is 10 times slower, how to optimize Clojure
> implementation performance?
>
> Java impl:
>
> import java.util.Scanner;
>
> public class Main {
> public static void main(String[] args) {
> Scanner sc = new Scanner(System.in);
> do {
> int num = sc.nextInt();
> if (num == 42)
> break;
> System.out.println(num);
> } while( true );
> }
> }
>
> Clojure impl:
>
> (import java.util.Scanner)
>
> (defn getNextInt [scanner term f x]
> (if (not= x nil)
> (apply f [x]))
>
> (let [val (. scanner nextInt)]
> (if (not= val term)
> (getNextInt scanner term f val))))
>
> (getNextInt (Scanner. System/in) 42 (fn [x] (println x)) nil)
>
> Thanx
>
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