One nitpick I noticed, reduce is eager, not lazy.
On Tue, Apr 15, 2014 at 9:25 AM, Alex Vzorov <alex.vzo...@gmail.com> wrote: > Hi, Cecil. > > The difference is that doseq is used to produce side-effects, which is > idiomatic, which is exactly what you did. When using doseq you can be > sure that it's body will evaluate, whereas with map, for, reduce you > can't - they expect pure functions, and produce lazy sequences, and there > in no way for them to know that you want these sequences evaluated. At > least, this is my understanding at the moment. > > Because you said you liked clean code, I'd like to point out that your > solution, although works, relies on mutating state of external vars, i.e. > producing side effects, which is not necessary, and looks spaghetti-like, > somewhat. > > Instead, you could modify return value of foo function to return a vector > of [result, time], or, because you seem to not care about the result, > time the function took to complete. > > It would look similar to what you already did: > > - first define a higher order function, that records executions time of a > supplied function: > > (defn timed [f] > (fn [& args] > (let [start (.getTimeInMillis (now)) > result (apply f args) > end (.getTimeInMillis (now))] > [result (- end start)]))) > > - define a timed version of foo: > > (defn foo' (timed foo)) > > - use it with doseq, because you are doing side-effects: > > (doseq [time (map second (map foo' numbers))] > ;; alternatively, you can use threading macro: (doseq [time (->> numbers > (map foo') (map second))] > (println "it took" time "ms")) > > And it works! Without mutating global state, with pure functions - what a > marvel. However, one piece is missing: number of threads the foo function > was using - the whole point of this typing, eh, programming, I mean. > You have 2 options here. First, the most obvious, is to return that number > in foo. Second is applicable if you're doing what I think you're doing - > applying the same computational algorithm using different number of > threads. If second is true, you know number of threads you are going to use > beforehand and foo could use them as input... ah, well, this is exactly > what you were doing, I know realize, numbers being number of threads to > use. Anyways, in light of this knowledge we can now rewrite doseq part as: > > (doseq [[time nthreads] (map (fn [n] [(second (foo' n)) n]) numbers)] > (println nthreads "threads took" time "ms to compute things")) > > Yay! > Note, that timed should work regardless of what function you supply to it. > > On Saturday, April 12, 2014 10:33:02 PM UTC+5:45, Cecil Westerhof wrote: >> >> 2014-04-12 18:19 GMT+02:00 Fergal Byrne <fergalby...@gmail.com>: >> >> >>> On Sat, Apr 12, 2014 at 4:55 PM, Cecil Westerhof <cldwes...@gmail.com>wrote: >>> >>>> (->> numbers >>>> (reduce timed-foo []) >>>> (map format-time) >>>> println) >>>> >>> >>> (->> numbers >>> (reduce timed-foo []) >>> (map format-time) >>> (map println)) >>> >> >> That was my first thought also, but that displays nothing. >> >> But the following works: >> (doseq [i (->> numbers >> (reduce timed-foo []) >> (map format-time))] >> (println i)) >> >> -- >> Cecil Westerhof >> > -- > 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. > -- 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.
