Hello Sean, thank you for the answer.
I used letfn not for recursive swearing, but for the localness. I thought the functions to be so special, nobody else will use it, so I put it into conway-PM. Is there a non recursive let for functions? Thanks for the hint about Lisppaste, didnt know that. Regards, alux On 13 Feb., 19:25, Sean Devlin <francoisdev...@gmail.com> wrote: > Alux, > Welcome to Clojrue! Thanks for posting this example. > > At first glance I would combine power-of-two? and what-power-of-2 into > one fn. Also, I would change the order you wrote the method calls in > to favor the .method style > > (defn power-of-2 > "Returns log_2(n) iff n is an exact pwoer of 2. nil otherwise" > (if (= (.bitCount (big-int n)) 1) > (dec (.bitLength (big-int n)))) > > Also, letfn is for mutually recursive fns (you know, the kind that > swear at each other :). I would move big-int, step & power-of-2 into > their own defns. That should clean up your definition of conway-PM. > > Sean > > PS - Do you use github or lisppaste? The general practice is to put > code in a pastebin, and simply include a link in the mailing list. > > On Feb 13, 11:48 am, alux <alu...@googlemail.com> wrote: > > > Hi, > > > I just finished my first (very small) Clojure program. I come from > > Java, so it will be everything but idiomatic Clojure, so I post it > > here and you may give as much criticism as you want. I'm here to > > learn. > > > It implements JHConway prime machine. The program does not want to be > > a quick prime generator (the algorithm is interesting but not quick at > > all), but it shall be/become a good implementation of this algorithm. > > >http://www.jstor.org/pss/2690263(Thefirst page is enough to > > implement the algorithm, even if the explanation will come on the next > > pages only.) > > > Started like: > > > (conway-PM) > > > It came up to 563 after about 6 hours on my 1.2 GHz Centrino ;-) > > > Thats the program, feel free to tell me stuff (or to ignore me, would > > be a lessen too :) > > > (defn conway-PM [] > > (let [ > > factors '(17/91 78/85 19/51 23/38 29/33 77/29 95/23 77/19 > > 1/17 11/13 > > 13/11 15/14 15/2 55/1) > > big-int-class (. 999999999999999999999999999999999 > > getClass)] > > (letfn [ > > (big-int [n];"makes a bigint from int, keeps n if > > bigint already" > > (let [current-class (. n getClass)] > > (if (= current-class big-int-class) > > n > > (. java.math.BigInteger > > valueOf n)))) > > (power-of-two? [n];"true iff the integer n is an > > power of 2." > > (= (. (big-int n) bitCount) 1)) > > (what-power-of-2 [n];"gets n from 2^n" > > (- (. (big-int n) bitLength) 1)) > > (step ;"Multiplies with the first factor to give an > > integer." > > [n, unused-factors] > > (let [factor (first unused-factors) > > rest-factors (rest unused-factors) > > dummy (* n factor)] > > (if (integer? dummy) > > dummy > > (step n rest-factors))))] > > (loop [seed 2] > > (let [next (step seed factors)] > > (if (power-of-two? next) > > (println (what-power-of-2 > > next))) > > (recur next)))))) > > > Regards, alux -- 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
