On Thu, Nov 19, 2009 at 1:23 PM, Sean Devlin <francoisdev...@gmail.com>wrote:
> Try clojure.contrib.seq-utils :) > > As a learning exercise, I'd recommend re-writing it to be lazy. Your > version is eager because it uses loop. In order to make it lazy, > you'd want to construct a lazy-seq. See the macro w/ the same name. > > Another choice is to use built-in functions, like this: > > (defn positions [pred coll] > (map second > (filter (comp pred first) > (map vector coll (iterate inc 0))))) (defn indexed [coll] (map vector (iterate inc 0) coll)) (defn positions [pred coll] (for [[i e] (indexed coll) :when (pred e)] i)) Seems to work: user=> (positions even? [1 1 2 9 3 4 8 7 6]) (2 5 6 8) (yes, I know there's already an "indexed" with similar semantics in clojure.contrib.) -- 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
