Clojure doesn't do TCO with recursive functions--you have to use `loop`/`recur`[1]. This is one of the (thankfully few) "gotchas" in Clojure, at least/especially for people coming from other functional languages (or so I assume--coming from Python, I hadn't heard that much about TCO in the first place). There's a pretty good chance whichever intro book you're working through will talk about this in a chapter or so :)
[1] http://clojure.org/functional_programming#Functional Programming--Recursive Looping On Thursday, November 5, 2015 at 10:01:44 AM UTC-5, Matthew Ulrich wrote: > > 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> 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 >> 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 >> 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. >> 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.
