Daniel, don't feed the WrexTroll On Jun 17, 12:44 am, Daniel Lyons <fus...@storytotell.org> wrote: > On Jun 16, 2009, at 10:34 PM, Wrexsoul wrote: > > > > > > > > > I'm shocked that this is missing from clojure.core: > > > (defn accum [f init coll] > > (loop [x init c coll] > > (if (empty? c) > > x > > (recur (f x (first c)) (rest c))))) > > > user=> (accum + 0 [1 2 3]) > > 6 > > user=> (accum + 0 [1 2 3 4 5]) > > 15 > > > This is one of the most basic, useful functions in functional > > programming. :) > > Indeed! It's called reduce: > > http://clojure.org/api#toc476 > > I'm shocked you haven't noticed it in the API documentation. Being > able to read is one of the most basic, useful skills in programming. > Especially if you want to be pompous without being an ass. > > > > > > > Here's any triangular number: > > > (defn tri [n] (accum + 0 (take n (iterate inc 1)))) > > > Here's a lazy seq of them all: > > > (def *tris* (for [i (iterate inc 1)] (tri i))) > > > This, however, is more efficient (and demonstrates another case where > > super-lazy-seq makes something very compact and readable): > > > (defn accum-map [f init coll] > > (super-lazy-seq [x init c coll] > > (if (seq c) > > (next-item x (f x (first c)) (rest c))))) > > > (def *tris* (rest (accum-map + 0 (iterate inc 1)))) > > > Notice how similar the accum-map code is to the accum code? With just > > lazy-seq it would not be as clear. :) > > Oh? What about compared to this: > > (use 'clojure.contrib.seq-utils) > > (def *tris* (reductions + (iterate inc 1))) > > — > Daniel Lyonshttp://www.storytotell.org-- Tell It! --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
