Hi again,
I am now trying to deal with formlets in a more principled fashion and thus
trying to implement, as Philip suggested, to use `send/formlet` and
`embed-formlet`. After a lot of tinkering, I still haven't figured out how
to actually process the formlet (without having to pass it around) with
embed-formlet. Here is the current example:
(define (debrief request)
(define test-formlet
(formlet
(div "Name:" ,{input-string . => . name})
(list name)))
(define (response-generator embed/url)
(html-wrapper
`((h1 "Testing Formlets")
(form ([action ,(embed/url testing)]
[method "POST"])
(p "Here is the displayed formlet")
;,@(formlet-display test-formlet) ;; THIS WORKS
,(embed-formlet embed/url test-formlet)
(input ([type "submit"]))
))))
The above works without `embed-formlet` with the following definition of
`testing`:
(define (testing request)
(define result (formlet-process test-formlet request))
(html-wrapper
`((h1 "Result")
(div
,(first result)))))
(send/suspend/dispatch response-generator))
But it does not work (or I can't figure out how it works) with
embed-formlet. How do I process the formlet, with the requirement that I do
not want to refer explicitly to `test-formlet`? Or is this not possible -
in which case, what does `embed-formlet` do that `formlet-processing`
doesn't? Any working example with embed-formlet is appreciate, even if it
is not the same as mine.
Thanks,
Marc
On Thu, Mar 16, 2017 at 2:11 PM, Marc Kaufmann <marc.kaufman...@gmail.com>
wrote:
> Thanks Philip. I checked out the links, but I fear that it's over my head,
> and that I would almost surely screw it up. For now I'll keep passing the
> parameters.
>
> Cheers,
> Marc
>
> On Tuesday, March 14, 2017 at 3:22:39 PM UTC-4, Philip McGrath wrote:
> > If you want it to be part of the continuation without having to pass it
> around as an argument, check out web cells (http://docs.racket-lang.org/
> web-server/stateless.html?q=web-server%2Flang%2Fwe#%28mod-
> path._web-server%2Flang%2Fweb-cells%29) or web parameters (
> http://docs.racket-lang.org/web-server/stateless.html?q=
> web-server%2Flang%2Fwe#%28mod-path._web-server%2Flang%2Fweb-param%29).
> >
> >
> >
> > -Philip
> >
> >
> >
> > On Tue, Mar 14, 2017 at 1:48 PM, Marc Kaufmann <marc.ka...@gmail.com>
> wrote:
> >
> >
> >
> > Thanks for the detailed answer Philip! Some of it is definitely over my
> head. The reason I don't pass around the id is that I use the html field
> exactly to track the id and wanted to avoid having to pass around the
> argument left and right - and the only ways to pass it on are via forms or
> by sticking it into the requested URL or by using continuations. I will
> give the continuation-style solution a shot though, it's probably cleaner
> to pass the id around as an argument.
> >
> > Cheers,
> > Marc
> >
> >
> >
> >
> >
> > On Tue, Mar 14, 2017 at 1:34 PM, Philip McGrath <
> phi...@philipmcgrath.com> wrote:
> >
> > In this case it will work despite being a hack, because you know that
> your id argument affects only the display stage, not the processing stage:
> however, you can't know in general that this will work for dynamically
> generated formlets, and personally I would therefore be reluctant to rely
> on this, both because it is fragile in terms of changes to your
> implementation of matrix-formlet that you might make later.
> >
> >
> > If you are using native continuations (i.e. not the stateless #lang
> web-server), you can use send/formlet or embed-formlet to deal with this
> correctly and easily. (At a lower level, you could also do something
> like(define-values (xexpr-forest bindings->result i)
> > ((matrix-formlet "3") 0))
> > to access the low-level rendering, processing function, and next
> allowable input integer directly.)
> >
> >
> > It is a little more tricky in #lang web-server, because your formlet and
> it's generated processing function are plain functions, and thus not
> serializable (see this old thread for discussion: https://groups.
> google.com/d/topic/racket-users/lMYWjodgpmo/discussion). The easy
> work-around is to keep the arguments you need to reproduce your formlet
> around as part of the closure, e.g. by rewriting your matrix-submission
> like this:(define (matrix-submission req id)
> > (define-values (number-of-ones user-id)
> > (formlet-process (matrix-formlet id) req))
> > ...)
> > The alternative is to either recompile the formlet library using #lang
> web-server/base or to implement your formlet at a low level using
> serial-lambda and not use any of the library tools.
> >
> >
> > In this specific case, though, if you are using this hidden input field
> just to remember the user id from one request to the next (i.e. you
> wouldn't ever change it on the client side with JavaScript or something),
> the best solution is not to put it in the form at all, but have it be part
> of the continuation. This could also have security advantages, if you
> cryptographically sign your continuations or store them on the server. If
> that works for your use case, you could simply write:
> > (define matrix-formlet
> >
> > input-string)
> > display it with
> > (matrix-submission
> > (send/suspend
> > (λ (k-url)
> > (response/xexpr
> > `(html (body (form
> > ((action "/the-matrix-submitted")
> > (method "post"))
> > ,@(formlet-display matrix-formlet)
> > (input ([type "submit"]))))))))
> > user-id)
> > and then define matrix-submission as(define (matrix-submission
> req user-id)
> > (define number-of-ones
> > (formlet-process matrix-formlet req))
> > ...)
> >
> >
> >
> > -Philip
> >
> >
> >
> >
> >
> > On Tue, Mar 14, 2017 at 12:01 PM, Marc Kaufmann <marc.ka...@gmail.com>
> wrote:
> >
> >
> > Hi,
> >
> >
> >
> > I have created a formlet like so:
> >
> >
> >
> > (define (matrix-formlet id)
> >
> > (formlet
> >
> > (#%# ,{input-string . => . ones}
> >
> > ,{(to-string (required (hidden id))) . => . user-id}
> >
> > )
> >
> > (values ones user-id)))
> >
> >
> >
> > I display this as follows:
> >
> >
> >
> > `(form
> >
> > ((action "/the-matrix-submitted")
> >
> > (method "post"))
> >
> > ,@(formlet-display (matrix-formlet user-id))
> >
> > (input ([type "submit"]))))
> >
> >
> >
> > and process it like this:
> >
> >
> >
> > (define (matrix-submission req)
> >
> > (define-values (number-of-ones user-id)
> >
> > (formlet-process (matrix-formlet "3") req))
> >
> > ...)
> >
> >
> >
> > While this works, the formlet I use to display and process are not
> really the same, since they are created on the spot, and created with
> different parameters. So far it seems to work, but I am worried that this
> will break down, and clearly this isn't the right way to go about creating
> parametrizable formlets.
> >
> >
> >
> > The questions are (i) is the above going to work despite being a hack,
> and (ii) is there a correct and easy way to do the same thing?
> >
> >
> >
> > Cheers,
> >
> > Marc
> >
> >
> >
> > --
> >
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