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 Lyons http://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 -~----------~----~----~----~------~----~------~--~---
