On Tue, Jan 26, 2010 at 9:17 AM, Nebojsa Stricevic <nebojsa.strice...@gmail.com> wrote: > Greetings, > > I'm new to Clojure and working my way through Project Euler problems > for learning. I wrote function for calculating prime number below some > integer value max. But it doesn't work for large numbers, causing > StackOverflowError. > > (defn primes-below > "calculates all primes bellow max" > [max] > (loop [numbers (range 2 max) primes []] > (if (empty? numbers) > primes > (let [p (first numbers) > numbers (filter #(pos? (rem % p)) numbers) > primes (cons p primes)] > (recur numbers primes))))) > > (primes-below 2000000) > > I guess problem is not with loop-recur, or am I wrong?
The problem is that 'filter' is lazy, and each time through the loop you wrap another layer of filter around numbers. So each time, (first numbers) is calling through one more layer of filter than the previous time. Eventually this gets deep enough to overflow the stack. Of course with this algorithm you *need* filter to be lazy, or you'd never get past the first iteration of the loop. I'm afraid you'll have to come up with a new algorithm. There are a few options, but I suppose you don't want too many hints yet? --Chouser http://joyofclojure.com/ -- 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
