That sounds like 'reductions': (reductions + [1 2 4 8]) ==> (1 3 7 15)
Chris On Wed, Dec 1, 2010 at 10:20 PM, Alex Baranosky <alexander.barano...@gmail.com> wrote: > My friend's playing with Haskell, and asked me how I'd write a function to > take a list and return a list of the sums like so: > (f [1 2 4 8]) > => [1 3 7 15] > So I told him about Haskell's scanl function. > Is scanl available in Haskell? > These were my two versions of it and some simple benchmarks: > (defn scanl > ([f seed coll] > (scanl f seed coll 1)) > ([f seed coll i] > (if (<= i (count coll)) > (cons (reduce f seed (take i coll)) > (scanl f seed coll (inc i)))))) > (println (scanl + 0 [1 4 5 9])) > (defn scanl2 [f seed coll] > (loop [f f seed seed coll coll acc []] > (let [cnt (count acc)] > (if (< cnt (count coll)) > (recur f seed coll (conj acc (reduce f seed (take (inc cnt) coll)))) > acc)))) > (println (scanl2 + 0 [1 4 5 9])) > (def first (with-out-str (time (scanl + 0 [1 4 5 9 6 7 8 9])))) > (def second (with-out-str (time (scanl2 + 0 [1 4 5 9 6 7 8 9])))) > (println first) > (println second) > > -- > 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
