[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
why tail recursion matters and why Java isn't it, was Re: lisp performance was Re: problems with lisp
On Tuesday, September 2, 2003, at 05:54 PM, Ken Anderson wrote:
> I don't believe you need a fundamental rewrite in Lisp any more often
then you do
> in another language.
> Generally, write your Lisp (or any other language really) in a clear
> straight forward manner. When you have a performance problem, use a
> profiler to find out where it is. Don't guess, not even if you're an
> expert. The 80/20 rule means you have to address performance, but
> most of the code can ignore it.
Ken, with all due respect, this is not right. Unless your functional
language (including Python) doesn't impose uniform tail-call
you can't get away without a fundamental rewrite.
What truly bothers me is that pl researchers and ll workers just don't
insight. There are two kinds of traversals for data (including natural
- those that follow the structure
(that's the essence of OOP dispatch, to call methods only;
loops are *not* OOP per se, though you can fit them in via
for the contrary, see Java)
- those that generate new data before they recur.
There is nothing else.
For the first, you can add 127,341 looping constructs because you
your programmer-clients won't understand recursion. But you will never
all cases. You will only do so if your language has TCO and you can
use your goto-with-parameters (aka tail calls) to match the
(aka references). You will always have to squeeze your program
into some unnatural looping structure to get decent performance for the