I used only the procedures provided by RnRS, instead of loading SRFI-13,
but you could use string-map if you want to. For those who prefer to roll
their own, here is a simple version of string-map! that mutates the string
in place:
(define (string-map! f str)
(do ((i 0 (+ i 1))) ((= i (string-length str)) str)
(string-set! str i (f (string-ref str i)))))
Or you could convert to a list, perform the mapping, and convert back, as I
did in my original version of the function. With string-map!, the caesar
function changes to this:
(define (caesar str n)
(define (char-plus c)
(let ((alpha "ABCDEFGHIJKLMNOPQRSTUVWXYZ"))
(if (not (char-alphabetic? c)) c
(let ((i (- (char->integer (char-upcase c)) 65)))
(string-ref alpha (modulo (+ i n) 26))))))
(string-map! char-plus str))
For purposes of Rosetta Code, it's probably better to avoid SRFI-13 and
stay with RnRS, as in my first version of the function.
On Mon, Mar 10, 2014 at 10:31 AM, Peter Bex <peter....@xs4all.nl> wrote:
> On Mon, Mar 10, 2014 at 10:26:56AM -0500, Phil Bewig wrote:
> > I would use an auxiliary function char-plus to add or subtract an offset
> to
> > a character:
> >
> > (define (caesar str n)
> > (define (char-plus c)
> > (let ((alpha "ABCDEFGHIJKLMNOPQRSTUVWXYZ"))
> > (if (not (char-alphabetic? c)) c
> > (let ((i (- (char->integer (char-upcase c)) 65)))
> > (string-ref alpha (modulo (+ i n) 26))))))
> > (list->string (map char-plus (string->list str))))
>
> If you're using srfi-13, you might as well change the final line to use
> string-map: (string-map char-plus str)
>
> Cheers,
> Peter
> --
> http://www.more-magic.net
>
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