Hi, On Feb 22, 2010, at 1:43 AM, Meikel Brandmeyer wrote:
> Hi, > > On Feb 22, 12:18 am, Johnny Kwan <johnny.c.k...@gmail.com> wrote: >> I'm really new to Clojure, but I'm under the impression that reduce would >> be better than apply, since I assume that apply would reify the entire >> sequence at once, whereas reduce would consume the sequence one by one. >> Could someone more familiar with the implementation weigh in on this? > > apply is lazy. > > user=> (defn test-apply [& xs] (prn (take 10 xs))) > #'user/test-apply > user=> (apply test-apply (iterate inc 0)) > (0 1 2 3 4 5 6 7 8 9) > nil > > Sincerely > Meikel Hmm, I don't know enough about how well the Java AOT compiler and JIT compiler optimizes this in general. But just because apply is lazy doesn't mean that when apply is finally realized, the entire sequence doesn't have to be reified to call the function. Reading through the implementation of .applyTo and .applyToHelper in clojure.lang.AFn makes this clear. Here's a concrete example: (time (reduce + (range 1 10000000))) ; 4.5 secs on my Macbook Air (time (apply + (range 1 10000000))) ; OutOfMemory error Whichever is faster depends on the size of the argument list, since apply is called once with the concrete arglist, and reduce is called many times with just 2 args. However, apply certainly seems to try to shove the entire sequence into an array, at least on the OSX Snow Leopard JVM. Thanks, Johnny -- 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 Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
