Rainer Joswig wrote:

> > How would you take a sequence of numbers in groups of 2 and print out
> > the numbers and their product?
> >
> > Here is my solution, but I'm sure some li5p h4x0r has a much more 1337
> > solution :)
> >
> > (setf nums (vector 21 47
> > 23 43
> > 24 29
> > 22 28
> > 22 53
> > 31 36
> > 22 56
> > 31 72))
>
> Remember that variables are introduced with DEFPARAMETER (or DEFVAR)
> and not with SETF.
>
> Also remember that all top-level variables should be by convention
> written like this: *nums*
>
> >
> > (loop for i from 0 below (car (array-dimensions nums)) by 2
> > do (progn
> > (let ((a (aref nums i))
> > (b (aref nums (1+ i))))
> > (format t "~A * ~A = ~A~%" a b (* a b)))))
>
> ARRAY-DIMENSION is not the best operation for a vector in
> general, since the vector could be one with a fill-pointer.
> LENGTH will give you the real used length of a vector.
>
> This solution is basically the same as yours but a bit
> differently written:
>
> (loop with size = (length *nums*)
> for i from 0 below size by 2
> for j from 1 below size by 2
> for a = (aref *nums* i) and b = (aref *nums* j)
> do (format t "~A * ~A = ~A~%" a b (* a b)))

(use srfi-43) ;; vector->list for Gauche
or
(require srfi/43) ;; vector->list for Racket

(require srfi/48) ;; format for Racket

(define nums
(vector 21 47
23 43
24 29
22 28
22 53
31 36
22 56
31 72))

(do ((i 0 (+ i 2)))
((= i (vector-length nums)))
(let ((both (vector->list nums i (+ i 2))))
(apply format #t "~a * ~a = ~a~%" `(,@both ,(apply * both)))))

21 * 47 = 987
23 * 43 = 989
24 * 29 = 696
22 * 28 = 616
22 * 53 = 1166
31 * 36 = 1116
22 * 56 = 1232
31 * 72 = 2232