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On Thu, 11 Jun 1998 10:23:51 -0500, "Kenneth D. Forbus"
<ils.nwu.edu at forbus> wrote:

>Maybe I'm old-fashioned, but I find DO -- which is part of the common
>lisp spec -- is just as easy to use, is more flexible, and displays
>well under pretty-printing.

Do you prefer

 (defun primes (n)
    (when (> n 1)
       (let* ((primes (list 2))
              (last primes)
              (max (floor (sqrt n))))
          (do ((i 3 (+ i 2)))
              ((> i n) primes)
             (do* ((next primes (rest next)))
                  ((or (null next)
                       (> (first next) max))
                   (rplacd last (list i))
                   (setq last (rest last)))
                (when (zerop (rem i (first next)))
                   (return)))))))

over

 (defun primes (n)
    (when (> n 1)
       (loop
         with primes = (list 2)
         with max = (floor (sqrt n))
         with last = primes
         for i from 3 to n by 2
         do (loop
              for p in primes
              until (> p max)
              never (zerop (rem i p))
              finally
                (rplacd last (list i))
                (setq last (rest last)))
         finally (return primes))))

then?

Curiously, in ACL4W 3.0.2, with '(optimize (speed 0) (safety 3)) the
second version is about 10% slower than the first; and with
speed3/safety0 they are 'bout the same.

(Yes, I admit neither one is a good example of lisp programming;
I'm just learning my way into CL ;)


                                                       /L/e/k/t/u




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