I actually mentioned the cycle function in my message, and that's what I was using, but the original question came up because accessing the nth item in a list takes linear rather than constant time.
I'd be interested to hear how what I was attempting violates the spirit of clojure. I was trying to work within the bounds of an existing abstraction, and to implement my changes in such a way as to not break other things that consume that abstraction. Incidentally, I don't believe the error I'm getting from proxy has anything to do with IPersistentVector being an interface, since you can clearly do: (proxy [clojure.lang.IFn] []) and that works fine (although obviously is not related to solving my particular problem). On Mar 8, 5:20 pm, Timothy Pratley <timothyprat...@gmail.com> wrote: > For your eueler problem consider using lazy functions cycle and range: > user=> (take 15 (cycle (range 5))) > (0 1 2 3 4 0 1 2 3 4 0 1 2 3 4) > Or is there some other behavior you need to create? > > Regarding proxy your main problem is that IPersistentVector is an > Interface (no implementation) so you would have to specify every > method. More sensibly you could proxy the concrete implementation > PersistentVector, however it does not have an empty constructor so you > would need to figure out exactly what you want to do. > user=> (proxy [clojure.lang.PersistentVector] []) > java.lang.IllegalArgumentException: No matching ctor found for class > clojure.proxy.clojure.lang.PersistentVector > > I would advise against proxying for this problem as it is complex and > not in the spirit of solving the problem in Clojure. > > Regards. > Tim. > > On Mar 9, 9:13 am, Paul Mooser <taron...@gmail.com> wrote: > > > > > I was playing around with some project euler problems, and I was > > thinking that the cycle function has an analog for vectors. I > > implemented a short simple method with the right behavior (at a simple > > surface level): > > > (defn cyclic-vector [v] > > (fn [x] > > (v (mod x (count v))))) > > > However, this obviously does not implement IPersistentVector. > > > Is there any easy way to implement something like this, and delegate > > the rest of the behaviors to the base vector object ? I realize this > > is probably possible with proxy, but I have not successfully made it > > work yet - proxying the IPersistentVector interface results in the > > following for me: > > > (proxy [clojure.lang.IPersistentVector] []) > > > java.lang.ClassFormatError: Duplicate method name&signature in class > > file clojure/proxy/java/lang/Object$IPersistentVector (NO_SOURCE_FILE: > > 2) > > > Is this an issue with proxy, or am I using it incorrectly ? I removed > > any extraneous code of my own, since the error occurs with just the > > minimal proxy usage shown above. I'm on trunk, revision 1326. --~--~---------~--~----~------------~-------~--~----~ 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 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 -~----------~----~----~----~------~----~------~--~---
