Re: scheme (format) question

[Kjetil S. Matheussen]

Mark Polesky:
> ;; Hi.
> ;;
> ;; How can I change the following code so that
> ;; it returns "2 0.25 0.3333"? That is: return
> ;; integers without decimal point, otherwise
> ;; round to as many decimal places as needed,
> ;; but not more than 4.
>
> (let ((a 2.0)
>      (b 1/4)
>      (c 1/3))
>  (format #t "~&~a ~a ~a" a b c))
>
> ;; After some experimenting, I found the
> ;; following solution, but I'd rather not have
> ;; to deal with all the incessant quasiquote
> ;; and unquote stuff. Is there a more elegant
> ;; solution?
> ;;
> ;; Thanks in advance.
> ;; - Mark
>
> (define (set-precision n)
>  (let* ((max-decimals 4)
>         (k (expt 10.0 max-decimals)))
>  (if (number? n)
>      (if (integer? n)
>          (inexact->exact n)
>          (/ (round (* n k))
>              k))
>      n)))
>
> (define (my-format bool string list-of-nums)
>  (apply format bool string (map set-precision list-of-nums)))
>
> (let ((a 2.0)
>      (b 1/4)
>      (c 1/3))
>  (my-format #t "~&~a ~a ~a" `(,a ,b ,c)))

Yes:

(let ((a 2.0)
     (b 1/4)
     (c 1/3))
 (my-format #t "~&~a ~a ~a" (list a b c)))



But better:

(define (my-format bool string . list-of-nums)
 (apply format bool string (map set-precision list-of-nums)))

(let ((a 2.0)
     (b 1/4)
     (c 1/3))
 (my-format #t "~&~a ~a ~a" a b c))



I would also think that 'format' has an option
to do this directly without calling 'set-precision',
but I don't know...