On Dec 2, 8:13 pm, "john.holland" <jbholl...@gmail.com> wrote:
> Thanks for all the replies. It seems to me that as general solutions to
> stack overflow, trampoline and recur are
> very valuable. I had gotten the mistaken idea that Scheme was somehow
> immune to the problem.
> My experiments in Scheme seemed to get to higher amounts of recursion
> before blowing up than my Clojure did,
> but they are both susceptible to it. Are there things like trampoline and
> recur in Scheme? In Lisp?
Well yes, but they are not explicitly specified since Scheme
automatically optimizes tail calls. Consider this example:
(define (fact n)
(if (< n 2)
1
(* n (fact (- n 1)))))
This is not tail recursive and eventually blows the stack ... in
Scheme and in Clojure.
(define (fact-accu n res)
(if (< n 2)
res
(fact-accu (- n 1) (* n res))))
Here, the recursive call is in tail position and gets optimized by the
Scheme compiler. In Clojure you would have to call recur instead,
otherwise your stack grows. In Scheme this is not necessary since the
optimization is always done if possible. Thus, there is no special
syntactic marker, i.e. reserved word, for this. (Same holds for mutual
recursion <-> trampoline).
In Common Lisp the situation is somewhat unfortunate, since tail call
optimization is implementation dependent. So, you cannot rely on it
and therefore loop/tagbody etc are your friends there.
Hope this helps,
Nils
>
> John Holland
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