Thanks, Sergio - this is a good way to construct the sieve. It took me a little while to convince myself that it's the same, but it's definitely a good solution.
In general, I guess it's not possible to generate an infinite sequence that utilizes the tail-call optimization.... it makes sense as there is no "tail". Have a good day, Matty On Wednesday, November 4, 2015 at 10:07:46 AM UTC-5, Sergio Rupena wrote: > > Hi > > You can try the following > > (defn dividers [primes n] > (take-while #(<= (* % %) n) primes)) > > (defn prime? [primes n] > (every? #(pos? (rem n %)) > (dividers primes n))) > > (defn range-peek [coll] > (iterate inc (-> coll peek inc))) > > (defn sieve > ([] (cons 2 (lazy-seq (sieve [2])))) > ([primes] > (let [p (->> primes > range-peek > (filter (partial prime? primes)) > first)] > (cons p (lazy-seq (sieve (conj primes p))))))) > > (last (take 10000 (sieve))) > > This version keeps the visited primes in a vector so it will grow in > memory but won’t overflow otherwise. > > Sergio > > On 04 Nov 2015, at 15:44, Matthew Ulrich <matty...@gmail.com <javascript:>> > wrote: > > All - > > I'm trying to generate a lazy sequence of primes using Erastosthenes Sieve > (from Abelson & Sussman) and am encountering some issues with lazy sequence. > > Here's what I have: > --- > > (defn divisible? > [input numerator] > (= 0 (mod input numerator))) > > (defn sieve > [stream] > (lazy-seq > (cons > (first stream) > (sieve (filter #(not (divisible? % (first stream))) (rest > stream)))))) > > (def primes (sieve (iterate inc 2))) > > --- > > This is fine now when I: > > => (take 5 (drop 1000 primes)) > (7927 7933 7937 7949 7951) > > > But when I: > > => (take 5 (drop 4000 primes)) > StackOverflowError clojure.lang.LazySeq.sval (LazySeq.java:40) > > > -- > > I understand how the StackOverflow occurs with the filter on the > recursively generated sequence... however I can't think of a way to make > this work.. > > I'm pretty new to clojure so I'm not very familiar with all of the > language features; is there some tool to help me realize this or should I > just go about the implementation in a different way? > > Thanks - have a great morning! > > Matty > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clo...@googlegroups.com <javascript:> > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+u...@googlegroups.com <javascript:> > 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+u...@googlegroups.com <javascript:>. > For more options, visit https://groups.google.com/d/optout. > > > -- 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/d/optout.
