Tassilo Horn <tass...@member.fsf.org> writes: >>> You should probably inline comp for your purposes. Note the reverse >>> call there. >>> >>> https://github.com/clojure/clojure/blob/d0c380d9809fd242bec688c7134e900f0bbedcac/src/clj/clojure/core.clj#L2267 >> >> Oh, that's a pity. I'd much vote for a left-to-right version >> complementing the current right-to-left `comp`. > > I created a JIRA issue and added a patch: > > http://dev.clojure.org/jira/browse/CLJ-1010
Now that's strange. If I adapt Yoshinori's code to use a list again and the left-to-right `comp*` instead of the reversing `comp`, I expected to get a reasonable benefit. I.e., that's the new code (https://gist.github.com/2908767). --8<---------------cut here---------------start------------->8--- (defn r-reduce [init updt pred retn f coll] (loop [stat init [h & r :as curr] coll acc (list identity)] (if (or (pred stat) (nil? r)) ;; comp* is left-to-right, so it doesn't reverse ((apply comp* acc) (retn curr)) (recur (updt stat) r (cons (partial f h) acc))))) (defn reduce-right [f coll] (r-reduce coll next nil? first f coll)) --8<---------------cut here---------------end--------------->8--- and that's the old version: --8<---------------cut here---------------start------------->8--- (defn r-reduce-old [init updt pred retn f coll] (loop [stat init [h & r :as curr] coll acc (vector identity)] (if (or (pred stat) (nil? r)) ;; Will reverse acc ((apply comp acc) (retn curr)) (recur (updt stat) r (conj acc (partial f h)))))) (defn reduce-right-old [f coll] (r-reduce-old coll next nil? first f coll)) --8<---------------cut here---------------end--------------->8--- This seems to prove that `comp*` is much faster than `comp` if there are many functions: --8<---------------cut here---------------start------------->8--- user> (time (apply comp* (take 2000000 (repeat identity)))) "Elapsed time: 0.078991 msecs" #<core$comp_STAR_$fn__4071 clojure.core$comp_STAR_$fn__4071@74cee5ed> user> (time (apply comp (take 2000000 (repeat identity)))) "Elapsed time: 1515.573253 msecs" #<core$comp_STAR_$fn__4071 clojure.core$comp_STAR_$fn__4071@4cb8cd94> --8<---------------cut here---------------end--------------->8--- But strangely, this 1.5 second benefit is completely lost somewhere: --8<---------------cut here---------------start------------->8--- user> (time (reduce-right-old - (range 2000000))) "Elapsed time: 3992.088322 msecs" -1000000 user> (time (reduce-right - (range 2000000))) "Elapsed time: 4125.689783 msecs" -1000000 --8<---------------cut here---------------end--------------->8--- Can someone enlighten me what's happening? Thanks, Tassilo -- 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
