lazy sequence question
I'm working my way through "Programming Clojure" and got an unexpected result with sequences: user> (take 10 (filter even? (iterate inc 1))) (2 4 6 8 10 12 14 16 18 20) user> (take-while #(< % 10) (iterate inc 1)) (1 2 3 4 5 6 7 8 9) user> (take 10 (filter #(< % 10) (iterate inc 1))) ; Evaluation aborted. The first two work but the third one hangs. Why? Thanks, Mike -- 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
Lazy sequence question
Hi everybody, I'd like to create a lazy sequence which has first element x and all the rest from another lazy sequence. I couldn't find a suitable function in the docs. Can somebody give a hint? Best regards PŁ -- 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
Re: lazy sequence question
On Dec 9, 10:35 pm, Mike K wrote: > The first two work but the third one hangs. Why? user> (take 5 (filter #(< % 10) (iterate inc 1))) (1 2 3 4 5) OK, I figured out that it won't hang with taking <= 9 elements, which is the total that pass the filter. But shouldn't it give me 9 items without hanging when I ask for 10 or more as in the first case? Mike -- 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
Re: lazy sequence question
There are only 9 items that satisfy your predicate. (take 10 ...) demands a 10th, and it keeps searching the (iterate inc 1) stream forever, endlessly searching for that 10th item it will never find. On Wed, Dec 9, 2009 at 9:41 PM, Mike K wrote: > On Dec 9, 10:35 pm, Mike K wrote: > >> The first two work but the third one hangs. Why? > > user> (take 5 (filter #(< % 10) (iterate inc 1))) > (1 2 3 4 5) > > OK, I figured out that it won't hang with taking <= 9 elements, which > is the total that pass the filter. > > But shouldn't it give me 9 items without hanging when I ask for 10 or > more as in the first case? > > Mike > > -- > 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 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
Re: lazy sequence question
> But shouldn't it give me 9 items without hanging when I ask for 10 or > more as in the first case? No. take returns a lazy sequence. The printer is trying to realize it in order to print it. It can't be completely realized until it's taken ten elements (at which point it's done, by definition). In realizing the sequence, the first nine items are collected. take wants one more. It tries to fetch it from the filtered lazy-seq. The filtered seq gets 10 from the iterate lazy-seq, which doesn't pass the filter. It gets 11, which doesn't pass the filter... Neither filter nor take know to abandon their attempt. That's how this works. Imagine if you wrote: user=> (take 10 (filter #(or (= 1000 %) (< % 10)) (iterate inc 1))) (1 2 3 4 5 6 7 8 9 1000) It just keeps on going until it's found ten elements. -- 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
Re: lazy sequence question
> Neither filter nor take know to abandon their attempt. That's how this > works. Ah, of course. Thanks Mark and Richard! Mike -- 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
Re: lazy sequence question
On Dec 9, 9:46 pm, Mark Engelberg wrote: > There are only 9 items that satisfy your predicate. (take 10 ...) > demands a 10th, and it keeps searching the (iterate inc 1) stream > forever, endlessly searching for that 10th item it will never find. Aww. You make it sound so sad. -- 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
Re: Lazy sequence question
Is conf what you're looking for? http://clojure.github.com/clojure/clojure.core-api.html#clojure.core/cons ~Kasper On 11/30/11 2:27 PM, Paweł Łoziński wrote: Hi everybody, I'd like to create a lazy sequence which has first element x and all the rest from another lazy sequence. I couldn't find a suitable function in the docs. Can somebody give a hint? Best regards PŁ -- 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
Re: Lazy sequence question
On 30 Lis, 22:31, Kasper Galschiot Markus wrote: > Is conf what you're looking for? > > http://clojure.github.com/clojure/clojure.core-api.html#clojure.core/... > > ~Kasper Of course. 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
