If you name the Y combinator, then you can write recursive anonymous functions:
<http://rosettacode.org/wiki/Y_combinator#Clojure> You can't use Clojure's recur as written because it isn't in tail position--the result of the function isn't just the value of the recur expression (in the first instance it is (* 2 (recur ...)) however I note that z is free in that expression, which looks suspicious. If your goal is to define a function that computes 2^n with tail-recursion, then consider threading an "accumulator" parameter through the recursive function; something like this: ((fun [acc x] (if (= x 0) acc (recur (* 2 acc) (dec x))) 1 5) Of course, you might consider a helper wrapper function that supplies the 1 "default" accumulator. Many functional languages optimize tail calls to jmp instructions; that's hard to do efficiently in general on the JVM because it doesn't support tail calls. I expect Clojure has designed recur to work the way it does because some algorithms depend on the tail call optimization, but the restrictions of recur make it possible to compile efficiently as a jmp. So it's a nice compromise. <http://clojure.org/special_forms#Special Forms--(recur exprs*)> HTH, Dominic On Wed, Jun 30, 2010 at 2:44 PM, Tim Robinson <tim.blacks...@gmail.com> wrote: > So I am reading On Lisp + some blogs while learning Clojure (I know, > scary stuff :) > > Anyway, I've been playing around to see if I can get an anonymous > recursive function to work, but alas I am still a n00b and not even > sure what Clojure's approach to this would be. > > How would I do this in Clojure?: > > My first attempt: > > ((fn [x] > (if (= x 0) > 1 > (* 2 (recur (dec z))))) 5) > > Then my second: > > ((fn [x] > (let [z (if (= x 0) > 1 > (* 2 x))] > (recur (dec z)))) 5) > > Ideally one could do: > > ((recursive-fn #( if (= % 0) 1 (* 2 %)) (recur it)) 5) > > > Obviously none work, and I believe I understand why. I just don't > understand how to actually do this or if for some reason Clojure > avoids this for some reason. > > I am not actually trying to accomplish a specific task, so the example > was made to be simple not meaningful. I'm just playing around to learn > recursive functions and Clojure style. > > Thanks, > Tim > > > > -- > 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 -- 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
