[plt-scheme] send/suspend return values

Jordan, Matthias,

Many thanks for your responses!

To make sure I understand, is it the the unquote-splicing call
, at loptions in my code that results in the second traversal?

 From Jordan's post:
> It seems that passing the data into make-form is the right way to do
> it.
Do you say this becuase it's better style - time complexity is the
same, right?

 From Matthias's post:
> If your sample code is really representative and your goal is to get
> these large list of "random" things directly into a web page (which is
> different from the above), you need to perform a loop fusion manually
> (aka deforestation).
Yeah, that was the goal.

> (which is different from the above)
By "above" are you referring to my original example?

Many thanks again!

Cheers,
David

On Sun, Nov 21, 2004 at 09:25:16AM -0800, Jordan Johnson wrote:
>  For list-related administrative tasks:
>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> 
> 
> On Sunday, November 21, 2004, at 07:11  AM, David J. Neu wrote:
> >My alternative is to generate the list of data and then pass it into
> >the procedure MAKE-FORM, however, I'd like to avoid looping through
> >the data set twice.
> 
> I'm not sure I understand your question.  You're already looping 
> through the data set a second time when you write , at loptions, and 
> moving the generation of the data outside your form-builder procedure 
> won't change that...
> 
> In fact, I'd argue it'd be better; as written, your make-form doesn't 
> even care what lrandoms is.  It seems that passing the data into 
> make-form is the right way to do it.
> 
> Is there any reason NOT to write it this way (given the same def'n of 
> random-number-options you provided):
> 
>   (define doit
>     (lambda (an)
>       (let* ((rands/opts (random-number-options an))
>              (lrandoms (car rands/opts))              ;; or better, use 
> let-values
>              (loptions (cadr rands/opts))
>              (lrequest (send/suspend (make-form an loptions)))
> 					;; add loptions arg to make-form, 
> 					and delete make-form's let-exps
>              (lbindings (request-bindings lrequest)))
>           (let ((lnum (extract-binding/single 'num lbindings)))
>             (send/finish
>              `(html
>                (center ,(format "You selected the number ~a" 
> lnum)))))))))
> 
> Let me know if I'm missing something...
> 
> jmj
> 
> >The real application is a web-based database application, but I
> >thought this self-contained example made the point more succinctly.
> >
> >Many thanks for any help!
> >
> >Cheers,
> >David
> >
> >
> >(require (lib "unitsig.ss")
> >         (lib "servlet-sig.ss" "web-server")
> >         (lib "servlet-helpers.ss" "web-server"))
> >
> >(unit/sig () (import servlet^)
> >
> >  (define random-number-options
> >    (lambda (an)
> >      (let loop ((ln an)
> >                 (lrandoms '())
> >                 (loptions '()))
> >        (if (zero? ln)
> >            (list lrandoms loptions)
> >            (let ((lrandom (random an)))
> >              (loop (sub1 ln)
> >                    (cons lrandom lrandoms)
> >                    (cons (list 'option (format "~a" lrandom)) 
> >loptions)))))))
> >
> >  (define make-form
> >    (lambda (an)
> >      (let ((llist (random-number-options an)))
> >        (let ((lrandoms (car llist))
> >              (loptions (cadr llist)))
> >        (lambda (k-url)
> >          `(html
> >            (center
> >             (form ((action ,k-url) (method "post"))
> >                   (p "Please select a number: ")
> >                   (p (select ((name "num")) , at loptions))
> >                   (p (input ((type "submit") (value "OK"))))))))))))
> >
> >  (define doit
> >    (lambda (an)
> >      ; I'd like to have the list of random numbers i.e. the variable 
> >lRANDOMS
> >      ; in procedure MAKE-FORM available here, i.e. have it returned in
> >      ; addition to lrequest
> >      (let ((lrequest (send/suspend (make-form an))))
> >        (let ((lbindings (request-bindings lrequest)))
> >          (let ((lnum (extract-binding/single 'num lbindings)))
> >            (send/finish
> >             `(html
> >               (center ,(format "You selected the number ~a" 
> >lnum)))))))))
> >
> >  (doit 20))
> >
> >
> --
> Jordan Johnson (Email manipulator #22483617)