On Wed, Mar 24, 2010 at 8:39 PM, Per Vognsen <per.vogn...@gmail.com> wrote: > On Wed, Mar 24, 2010 at 8:21 PM, Glen Rubin <rubing...@gmail.com> wrote: >> I wrote the following code to produce a lazy sequence of the triangle >> numbers. (triangle numbers are the series of numbers: 1, 1+2, 1+2+3, >> etc...) >> >> (defn tri-nums [] >> "prduce a lazy sequence of triangle numbers" >> (let [triangles (map #(range 1 %) (iterate inc 2))] >> (map #(reduce + %) triangles))) >> >> However, I now have produced a large triangle number (76576500) and >> want to know which triangle number it is (e.g. the first, second, >> third, etc...) > > Why not index the sequence with the 'indexed' function up front? > >> So, I wrote the following code which should accept a triangle number >> as input and tell you which one it is in the series: >> >> (defn which-tri [z] >> (loop [x 1 y (first (tri-nums))] >> (cond >> (= y z) >> x >> (< y z) >> (recur (inc x) (first (rest (tri-nums)))) >> true >> (println "no such tri-num")))) >> >> >> The problem is that this function works for the first two triangle >> numbers (1, 3), but then just sits there doing nothing on any higher >> (6, 10, etc...).
Sorry, I misread your code. I was confused by your variable naming convention: x is usually the argument to the function. The problem is actually that your recur always passes the same unchanging argument for x: (first (rest (tri-nums))). (You also shouldn't be calling tri-nums from scratch every time.) -Per -- 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 To unsubscribe from this group, send email to clojure+unsubscribegooglegroups.com or reply to this email with the words "REMOVE ME" as the subject.
