If you want caching behavior, then use it as a sequence. If you want faster iteration, use it via reduce. The whole point of this change is to open the faster reduce path, which you won't get if you also cache.
I did some research a few months back via crossclj looking at how people typically use iterate. I can't actually remember finding any use cases other than inc or something similar (but it's been a while). > On Apr 2, 2015, at 6:11 PM, Nicola Mometto <brobro...@gmail.com> wrote: > > > The recent changes to iterate come with an interesting consequence: > reducing an iterate multiple times will cause the entire chain of x, (f > x), (f (f x)) .. to be recalculated every time. > > I'd argue that this is not desiderable and a regression (even though > probably one considered by design), and that this change in behaviour is > going to produce a degradation in performance when the function to > iterate actually does some computation rather than being a trivial > function like the one used in the benchmarks in the CLJ-1603 ticket > (inc) since its result won't be cached. > > If changing the new behaviour is out of the question I'd suggest to at > least document this new behaviour. The docstring of iterate talks about > returning a lazy-seq while when used with reduce it is actually a > generator. > > To show what I mean here's a silly example using Threa/sleep to simulate > computation: > > Clojure 1.7.0-alpha5 > user=> (def a (iterate #(do (Thread/sleep 2) (inc %)) 0)) > #'user/a > user=> (time (reduce (fn [_ x] (if (= 50 x) (reduced nil))) nil a)) > "Elapsed time: 106.385891 msecs" > nil > user=> (time (reduce (fn [_ x] (if (= 50 x) (reduced nil))) nil a)) > "Elapsed time: 0.560275 msecs" > nil > > Clojure 1.7.0-master-SNAPSHOT > user=> (def a (iterate #(do (Thread/sleep 2) (inc %)) 0)) > #'user/a > user=> (time (reduce (fn [_ x] (if (= 50 x) (reduced nil))) nil a)) > "Elapsed time: 109.088477 msecs" > nil > user=> (time (reduce (fn [_ x] (if (= 50 x) (reduced nil))) nil a)) > "Elapsed time: 109.51494 msecs" > nil > -- 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.
