[Ur] Compilation error using onchange with ccheckbox

[Sergey Mironov]

You may check the type signatures by consulting basis.urs from the
Ur/Web's repo. Among other 'built-in' declarations, we may find there

val ccheckbox : cformTag ([Value = bool, Size = int, Source = source
bool, Onchange = transaction unit] ++ boxAttrs ++ inputAttrs) []

...  Onchange = transaction unit ...

That is how Juian may 'know in advance' the correct style :)

Regards,
Sergey



2015-07-24 15:30 GMT+03:00 Julian Squires <julian at cipht.net>:
> On Fri, Jul 24, 2015 at 7:49 AM, Graham Hopper
> <graham at garden-images.co.uk> wrote:
>>             <ccheckbox onchange={fn _ => alert "Changed!"}/>
>
> Try
>   <ccheckbox onchange={alert "Changed!"} />
>
>> The error is long winded but I think the important part is:
>>
>>    Need:
>> <UNIF:U52::{Type}> ++ [Onchange = <UNIF:U69::Type> -> transaction {}]
>>   Field:  #Onchange
>> Value 1:  transaction {}
>> Value 2:  <UNIF:U69::Type> -> transaction {}
>> Incompatible constructors
>> Have:  transaction {}
>> Need:  <UNIF:U69::Type> -> transaction {}
>
> Onchange has the signature transaction unit, where as you might have
> expected it to be like the mouse events (onclick, et cetera) which
> have signature mouseEvent -> transaction unit, which is why they are
> typically written with an anonymous function that discards its
> arguments as you did above.
>
> Hope this helps,
>
> --
> Julian Squires
>
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