Hi Marc,
Most formlets are typed as `(formlet/c (or/c false/c binding?))` where
the `binding?` is returned when the thing is there and the `#f` is
returned when it isn't. However, if you use `required`, then an
exception is thrown on the `#f` because the form element must be
present. Formlets like `input-string` include a call to `required`. I
think that you either want to handle the `#f` or use `default` to have
a default value present. Similarly most formlets like `text-input`
have an optional `#:value` keyword for starting them off with a value.
I think a better form DSL could be built out of formlets that
automatically did client & server-side checking with looping
re-submission until correct, etc. But that's not what formlets are yet
and you have to roll it yourself.
Jay
On Sun, Jan 10, 2016 at 9:05 PM, Marc Kaufmann
<marc.kaufman...@gmail.com> wrote:
> Thanks.
>
> Another question about formlets: when I use (formlet-process formlet-name)
> it will often raise errors when a field doesn't have a value. Is there an
> easy way of capturing errors, in particular to show the form as it was
> entered by the user, but with an error message at the top, rather than
> blowing up?
>
> One way I can imagine doing this is to catch the errors via (with-handlers
> ... ), and then resend the form with previous answers pre-populated. So, I
> would do the following, where 'answer' is the string ("Yes" or "No") that
> was associated with the checked answer previously.
>
> (define (rg-formlet answer)
> (define (was-answer? a)
> (equal? a answer))
> (formlet
> (label
> ,{(radio-group '("Yes" "No") #:checked was-answer?) . => . answer})
> answer))
>
> Is this the way to do it, or is there an easier way (since forms with
> missing elements can't be such a rarity - and yes, I'll do checking on the
> client-side as well).
>
> Thanks,
> Marc
>
> On Sun, Jan 10, 2016 at 5:08 PM, Jay McCarthy <jay.mccar...@gmail.com>
> wrote:
>>
>> On Sun, Jan 10, 2016 at 3:50 PM, Marc Kaufmann
>> <marc.kaufman...@gmail.com> wrote:
>> > Hi,
>> >
>> > I manage to get the basic formlets to work, and tried the radiogroup,
>> > but it
>> > fails with the following error: "input-group: invalid selection #f",
>> > even
>> > though I had it selected. After some playing around, I saw that there
>> > are
>> > two input_0 fields being sent on submit, since I have another formlet on
>> > the
>> > same page (with a separate formlet-display and formlet-process).
>> >
>> > My question is: If I use formlets, do I have to put all the formlets
>> > into
>> > one big formlet on every page, as otherwise fields will have the same
>> > name
>> > attribute, and there will be clashes?
>>
>> Each form can have only one formlet. There can be different forms on a
>> page, I believe.
>>
>> Jay
>>
>> > Thanks,
>> > Marc
>> >
>> >
>> > --
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>>
>>
>>
>> --
>> Jay McCarthy
>> Associate Professor
>> PLT @ CS @ UMass Lowell
>> http://jeapostrophe.github.io
>>
>> "Wherefore, be not weary in well-doing,
>> for ye are laying the foundation of a great work.
>> And out of small things proceedeth that which is great."
>> - D&C 64:33
>
>
--
Jay McCarthy
Associate Professor
PLT @ CS @ UMass Lowell
http://jeapostrophe.github.io
"Wherefore, be not weary in well-doing,
for ye are laying the foundation of a great work.
And out of small things proceedeth that which is great."
- D&C 64:33
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