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List:       racket-users
Subject:    [plt-scheme] Printing
From:       jensaxel () soegaard ! net (=?ISO-8859-1?Q?Jens_Axel_S=F8gaard?=)
Date:       2005-10-15 20:24:10
Message-ID: 4351656A.9050007 () soegaard ! net
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Joe Marshall wrote:
> As it happens, I wanted to do this last week.
> Here is my solution:
> 
> (define (format-float float digits)
>   (let* ((numerals (number->string (round (* (inexact->exact float)
> (expt 10 digits)))))
>          (length   (string-length numerals))
>          (dot      (- length digits)))
>     (string-append
> 
>      (if (< dot 0) "0" (substring numerals 0 dot))
>      "."
>      (if (< dot 0)
>          (string-append (make-string (- dot) #\0) numerals)
>          (substring numerals dot length)))))

I see that you use round, which rounds to even. Which makes
sense in numerical calculations, where you hope the rounding
errors to the two sides will cancel - but is it normal to
use for formatting?

Perhaps the formating section in R3RS should be revived?

   > (format-float -0.5 0)
   "0."
   > (format-float -0.05 1)
   "-.1"
   > (format-float -0.005 2)
   ".-1"                           ; ?
   > (format-float -0.0005 3)
   "0.0-1"
   > (format-float -0.0005 4)
   "0.00-5"

-- 
Jens Axel S?gaard




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