I'm new to clojure as well, so someone please correct me if the following
explanation is wrong, but I'll give it a shot :).
The JVM does not natively support TCO; clojure uses the recur form to
accomplish what is effectively the same thing despite that shortcoming of
its host. The recur form works by jumping back to either the loop (or, if
there is no loop form, the defn/fn), and rebinding those scoped variables
to the value of the recur's arguments.
In your example:
(loop [n number factorial 1] ;; This will be the "target" of the
recur
(if (zero? n) ;; If n is zero,
factorial ;; return the value of
factorial
(recur (dec n) (* factorial n)))) ;; otherwise, jump to the loop,
rebinding n to (dec n) and factorial to (* factorial n)
I hope that this made sense :).
On Sunday, April 15, 2012 11:37:35 AM UTC-4, Anto wrote:
>
> I'm very new to Clojure. And I was pretty much interested to learn
> about vectors, list . maps in clojure.
>
> I have a code like this :
>
> (defn factorial-1 [number]
> "computes the factorial of a positive integer
> in a way that doesn't consume stack space"
> (loop [n number factorial 1]
> (if (zero? n)
> factorial (recur (dec n) (* factorial n)))))
>
> (println (time (factorial-1 5)))
>
>
> which argues that it does tail recursion optimization. I found this
> code on net. Can anyone explain me what does the last three lines
> does:
>
> (loop [n number factorial 1]
> (if (zero? n)
> factorial (recur (dec n) (* factorial n))))
>
> Thanks in advance.
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