[Ur] Set / Update values within a structure

Fri Nov 10 17:53:13 EST 2017

Hi Adam

I tried to create a sample from what I understand about your suggestion,
but of course I got it wrong.
Following is the code (which doesn't compile), which would demonstrate what
I'm trying to do (look for 4 forward slashes ////)

fun debugMe a =
        alert a;
        ////can't read from source n here, because it's defined within
main(), below doesn't compile
        fnn <- get n;
        fnn()

structure AB = Mymaths.Make(struct
                               val callback = debugMe
                           end)

fun main()=
  n <- source Nil;
  lss <- source Nil;
let
    fun callMe () =
        x <- AB.simple "test";
        debug x

    fun anotherCallback()
        //iterate over source lss and do something

in
    //Some code to change the callback debugMe to anotherCallback() but what ?!
    set n anotherCallback   ////this doesn't work
    return <xml>
        <body>
            <h1> Sample </h1>
            <button value="Click Me" onclick={fn _ => callMe()}></button>
        </body>
        </xml>
end

Thanks

On Fri, Nov 10, 2017 at 1:45 PM, Adam Chlipala <adamc at csail.mit.edu> wrote:

> You can register a callback that, when called, reads another callback out
> of a [source] and calls it.  Is that sufficient?
> On 11/10/2017 04:19 PM, Nitin Surana wrote:
>
> Hi Adam
>
> Thanks for responding. Is there any alternative to change the callback ? I
> want to trigger a urweb function defined within `let` block upon a
> javascript event.
> Since, the function is within `let` block (because it needs access to
> certain variables within the parent function), I'm unable to use execF(...)
> from javascript.
>
> Also, is `ref` not supported in urweb ?
>
> Thanks
>
> On Fri, Nov 10, 2017 at 4:48 AM, Adam Chlipala <adamc at csail.mit.edu>
> wrote:
>
>> On 11/09/2017 10:42 PM, Harshita Kasera wrote:
>>
>> What I ultimately want to achieve is to be able to change the callback
>> function *debugMe* at a later point of time. Is it possible to set or
>> update values within a structure at a later point of time?
>>
>>
>> No, module (structure) fields can't be modified at runtime in Ur/Web or
>> ML.  Therefore, the module system is not the right tool for runtime
>> rewriting of callbacks.
>>
>
>
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-- 
Regards
Nitin Surana
MS Computer Science
323-690-6529
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