[plt-scheme] C-style Printf Format Convention?

On May 12, 2004, at 5:07 AM, ifconfig wrote:

>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>
> If all you need is to choose the number of digits, why not write a 
> function
> to do it? I don't think something exist in standard libraries.
>
> (define (limit-digits x num)
>   ; x - number, num - number of digits after the decimal point
>   (define (iter l n t)
>     ; l - the number-string, as a list
>     ; n - number of digits left
>     ; t - has decimal point been encountered yet?
>     (if t
>         (if (> n 0)
>             (cons (car l) (iter (cdr l) (- n 1) #t))
>             empty)
>         (cons (car l) (iter (cdr l) n (equal? (car l) #\.)))))
>   (list->string (iter (string->list (number->string x)) n #f)))
>
>
>> (limit-digits 12345.678901234567 20)
> "12345.678901234567"
>> (limit-digits 12345.678901234567 10)
> "12345.6789012345"
>> (limit-digits 12345.678901234567 5)
> "12345.67890"
>> (limit-digits 12345.678901234567 1)
> "12345.6"

Gluurg.  How about something simple and numeric:

;; warning!  untested code alert!

(define (limit-digits x num)
   (let ([y (expt 10 x)])
     (number->string (/ (exact->inexact (round (* num y))) y))))

... or something like that.  Plus, this code rounds rather than 
truncating.

john

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