Nice. Are there any technical reasons this isn't the default implementation of mapcat in Clojure.core?
On Mon, Aug 22, 2011 at 9:27 AM, Meikel Brandmeyer <m...@kotka.de> wrote: > Hi, > > Am 22.08.2011 um 16:32 schrieb Asim Jalis: > >> Is there a way to rewrite mapcat (or apply concat) so that they don't >> evaluate the incoming seq unnecessarily? > > user=> (defn f [[x]] (println "Computing x:" x) [(inc x)]) > #'user/f > user=> (defn lazy-mapcat > [f coll] > (lazy-seq > (when-let [s (seq coll)] > (concat (f (first s)) (lazy-mapcat f (rest s)))))) > #'user/lazy-mapcat > user=> (->> [0] (iterate f) (take 0)) > () > user=> (->> [0] (iterate f) (apply concat) (take 0)) > Computing x: 0 > Computing x: 1 > Computing x: 2 > () > user=> (->> [0] (iterate f) (mapcat identity) (take 0)) > Computing x: 0 > Computing x: 1 > Computing x: 2 > () > user=> (->> [0] (iterate f) (lazy-mapcat identity) (take 0)) > () > > Sincerely > Meikel > > -- > 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
