Deeply nested lazy seq generation? Try wrapping the main sequence in a doall at each iteration of the outer loop.
On Wed, Sep 4, 2013 at 11:53 PM, John Gabriele <jmg3...@gmail.com> wrote: > I tried implementing the sieve of Eratosthenes in Clojure. The approach is > to loop while (A) keeping my current list of numbers which have not yet > been eliminated, and (B) keeping track of the number I'm "on" (checking for > multiples thereof). > > Here's what I came up with (in a foo.clj file): > > ~~~clojure > (declare remove-multiples-of) > (declare next-one-after) > > (defn main > [max-num] > (let [starting-nums (range 2 max-num)] > (loop [new-nums (remove-multiples-of 2 starting-nums) > new-num (next-one-after 2 new-nums)] > (if (or (nil? new-num) > (> new-num (* 0.5 max-num))) > new-nums > (recur (remove-multiples-of new-num new-nums) > (next-one-after new-num new-nums)))))) > > (defn remove-multiples-of > "Removes all multiples of n (but not $n * 1$) from xs." > [n xs] > (remove (fn [x] (and (> x n) > (zero? (rem x n)))) > xs)) > > (defn next-one-after > "It's assumed that xs is an ordered sequential collection of positive > integers, and that n is among xs. Returns the element right after n, unless > n is the last element --- if that's the case, just returns nil." > [n xs] > (second (drop-while (fn [x] > (not= x n)) > xs))) > > ;;--------------------------- > (println (last (main 5000))) > ~~~ > > Running that (via `lein exec foo.clj`), it appears to work. > > However, if I change that 5000 to 50000, I get a long disapproving-looking > stack trace starting with java.lang.StackOverflowError. Why is it > overflowing? > > Thanks! > > -- > -- > 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 > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > -- -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
