ahhh... to answer my own question (and if I had looked at the code and the API a bit closer), it turns out that "recur" can only be used in tail-position... and your code (as a tree-recursor) would not benefit from this.
On Dec 4, 5:39 pm, Daniel Eklund <[EMAIL PROTECTED]> wrote: > oops... > > I am just learning the language right now.... and just quickly looked > at what you did... > Would the use of "recur" instead of self-calls potentially help > consuming stack space? > > http://clojure.org/special_forms#toc10 > > On Dec 4, 5:37 pm, Daniel Eklund <[EMAIL PROTECTED]> wrote: > > > I > > > On Dec 4, 2:55 pm, PeterB <[EMAIL PROTECTED]> wrote: > > > > Hi, > > > > I downloaded clojure_20080916.zip and had a go with a simple tree > > > benchmark (cut-down version of the one in the computer language > > > shootout http://shootout.alioth.debian.org/). > > > > The Java version is pretty simple and runs in about 2s on my laptop: > > > > public class Main > > > { > > > public static void main(String[] args) > > > { > > > System.out.println("result: " + sumTrees(10000, 10)); > > > } > > > > public static int sumTrees(int iterations, int depth) > > > { > > > int i; > > > int sum = 0; > > > > for (i = 1; i <= iterations; i++) > > > sum += TreeNode.bottomUpTree(i, depth).itemCheck() + > > > TreeNode.bottomUpTree(-i, depth).itemCheck(); > > > return sum; > > > } > > > > public static class TreeNode > > > { > > > private TreeNode left, right; > > > private int item; > > > > TreeNode(int item) > > > { > > > this.item = item; > > > } > > > > TreeNode(int item, TreeNode left, TreeNode right) > > > { > > > this.left = left; > > > this.right = right; > > > this.item = item; > > > } > > > > private static TreeNode bottomUpTree(int item, int depth) > > > { > > > if (depth > 0) > > > return new TreeNode(item, > > > bottomUpTree(2*item-1, > > > depth-1), > > > bottomUpTree(2*item, > > > depth-1)); > > > else > > > return new TreeNode(item); > > > } > > > > int itemCheck() > > > { > > > if (left == null) > > > return item; > > > else > > > return item + left.itemCheck() - right.itemCheck(); > > > } > > > } > > > > } > > > > The Clojure version is considerably more compact and elegant: > > > > (defn make-tree [item depth] > > > (if (zero? depth) > > > (list item nil nil) > > > (let [item2 (* 2 item) depth-1 (dec depth)] > > > (list item (make-tree (dec item2) depth-1) (make-tree item2 > > > depth-1))))) > > > > (defn check-tree [tree] > > > (if (nil? tree) > > > 0 > > > (let [[i l r] tree] (- (+ i (check-tree l)) (check-tree r))))) > > > > (defn sum-trees [iterations depth] > > > (let [sum #(+ (check-tree (make-tree % depth)) > > > (check-tree (make-tree (- %) depth)))] > > > (reduce #(+ %1 %2) 0 (map sum (range 1 (inc iterations)))))) > > > > (time (println "result:" (sum-trees 10000 10))) > > > > However, there is a heavy price to be paid for this elegance: > > > 'Elapsed time: 100730.161515 msecs' > > > > Ouch! That's rather disappointing :-( > > > Any suggestions for improving the performance? --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
