[plt-scheme] Printing

Before going on, i apologize for "hijacking" this thread. i did this
because it seems i have some problems posting directly to the list. i
did try it some time back (DrScheme v.2xx) and neither did i see my
message in the list nor did i get an answer. i just tried it again
about an hour ago and though i'm not impatient, i'm not sure anybody
received my message with the subject "Numbers and i18n". if you did,
accept this apology.

However, i have something to contribute to this thread as well. i
tried the module you posted and
  (number->format-decimal 3.145 2)
comes back with
  string-ref: expects 2 arguments, given 3: "3.14" 1 #\.
in v.301.7

i will not go ahead with what i wrote in the message concerning
internationalization and numbers, as i cannot be sure i'm not flooding
the list.

If you did not receive that message and you have some idea as to what
i'm doing wrong (or why i cannot seem to find a way to have my mailing
list password emailed to me)-: i would appreciate your pointers.

-- evangelos


On 10/15/05, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
> This is a part of my collects, with contracts and friends, used in a
> quotster and stock evaluation program. I have meant to put such
> "contracted" code up at Planet for a while, but time just disappears.
> -- Matthias
>
>
> (module decimals mzscheme
>
>    (require
>     (lib "string.ss" "srfi" "13")
>     (lib "contract.ss"))
>
>    ;; Number Natural -> String -> Boolean
>    ;; is the decimal point at the right place in the string
>    (define (post-number->format-decimal _ n)
>      (define (formatted-number-as-string str)
>        (and (string? str)
>             (char=? (string-ref str (- (string-length str) n 1) #\.))))
>      formatted-number-as-string)
>
>    ;; Any -> Boolean
>    (define (real-or-rational x)
>      (or (inexact? x) (integer? x) (real? x)))
>
>    (provide/contract
>
>     [number->format-decimal
>      ;; convert a number into a formatted decimal string
>      ;; given: 10.321 wanted: "10.32"
>      ((flat-named-contract 'real-or-rational real-or-rational)
>       natural-number/c
>       . ->d .
>       post-number->format-decimal)]
>
>     [number->decimal-string
>      ;; convert a number into a decimal string
>      (number? . -> . string?)])
>
>    ;; Number N -> String
>    ;; turn the number x into a string with num digits after the decimal
> point
>    (define (number->format-decimal x num)
>      (let ([split (regexp-match "([0-9]*)\\.([0-9]*)"
> (number->decimal-string x))])
>        (format "~a.~a" (cadr split) (string-pad-right (caddr split) num
> #\0))))
>
>    ;
> ------------------------------------------------------------------------
> ---
>    ; Number -> String
>    ; turns a number into a string with decimal representation
>    ; Matthew's code
>    (define (number->decimal-string x)
>      (cond
>        [(or (inexact? x) (integer? x)) (number->string x)]
>        [(not (real? x)) ;; complex
>         (let ([r (real-part x)]
>              [i (imag-part x)])
>          (format "~a~a~ai"
>                   (number->decimal-string r)
>                   (if (negative? i) "" "+")
>                   (number->decimal-string i)))]
>        [else
>         (let ([n (numerator x)]
>               [d (denominator x)])
>           ;; Count powers of 2 in denomintor
>           (let loop ([v d][2-power 0])
>             (if (and (positive? v) (even? v))
>                 (loop (arithmetic-shift v -1) (add1 2-power))
>                 ;; Count powers of 5 in denominator
>                 (let loop ([v v][5-power 0])
>                   (if (zero? (remainder v 5))
>                       (loop (quotient v 5) (add1 5-power))
>                       ;; No more 2s or 5s. Anything left?
>                       (if (= v 1)
>                           ;; Denominator = (* (expt 2 2-power) (expt 5
> 5-power)).
>                           ;; Print number as decimal.
>                           (let* ([10-power (max 2-power 5-power)]
>                                  [scale (* (expt 2 (- 10-power 2-power))
>                                            (expt 5 (- 10-power
> 5-power)))]
>                                  [s (number->string (* (abs n) scale))]
>                                  [orig-len (string-length s)]
>                                  [len (max (add1 10-power) orig-len)]
>                                  [padded-s (if (< orig-len len)
>                                                (string-append
>                                                 (make-string (- len
> orig-len) #\0)
>                                                 s)
>                                                s)])
>                             (format "~a~a.~a"
>                                     (if (negative? n) "-" "")
>                                     (substring padded-s 0 (- len
> 10-power))
>                                     (substring padded-s (- len 10-power)
> len)))
>                           ;; d has factor(s) other than 2 and 5.
>                           ;; Print as a fraction.
>                           (number->string x)))))))])))
>
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>


--
if feeling is first who pays any attention to the syntax of things
will never wholly kiss you
-- ee cummings