I think Stewart's code was more for exemplary purposes, to demonstrate the use of recur in tail position. A more idiomatic approach might look like this:
(defn factorial [n] (apply * (range 1 (inc n)))) On Oct 17, 12:43 pm, Joel L <[EMAIL PROTECTED]> wrote: > This is interesting as I hit a similar stumbling block when I was > first playing with recur. I'm new to Lisp though not completely new to > functional programming, and have a style question about your solution: > > Is there a particular reason you chose to arity overload the factorial > function rather than use the loop construct to include an > accumulator? > > eg: > (defn factorial [n] > (loop ([acc 1, i n] > (if (= i 0) acc > (recur (dec i), (* acc i))))) > > The reason I ask is I've always been a little bothered by having to > have a second 'accumulator version' of functions in functional > languages, especially since they're often meaningless out of context > (how can factorial take a second argument?) I really like loop..recur > because it allows the accumulator version to be hidden. Does that make > sense? Is there a general preference for the non-loop version? > > I'm absolutely loving clojure by the way! > > On Oct 13, 2:06 pm, "Stewart Griffin" <[EMAIL PROTECTED]> wrote: > > > 2008/10/13 Stuart Halloway <[EMAIL PROTECTED]>: > > > > Hi Michael, > > > > The multiplication by n comes after the recur. > > > > Cheers, > > > Stuart > > > >> Giving the factorial function as: > > > >> (def factorial > > >> (fn [n] (cond (= n 1) > > >> (> n 1) (* n (recur (dec n)))))) > > > >> the compiler complains "Can only recur from tail position". > > >> Isn't really the recur in tail position? It is the last expresson to > > >> be evaluated. > > > Hello, > > > Following on from what Stuart said, here is a version with recur that > > uses an accumulator to avoid your problem: > > > (defn factorial > > ([n] > > (factorial n 1)) > > ([n acc] > > (if (= n 0) acc > > (recur (dec n) (* acc n))))) > > > Also, your method would return nil for (factorial 0), which should be > > 1, so I adjusted the termination condition to: (= n 0). > > > Regards, > > > Stewart Griffin --~--~---------~--~----~------------~-------~--~----~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
