[Ur] New attempt to wrap a simple JS datepicker library (Pikaday) to use with Ur/Web

Fri Aug 7 23:19:19 EDT 2015

Haven't read all of this yet, but...
1) Try putting the active tag after the form. That might (but might
not) get it to compile, though it's not a particularly nice solution.
2) The different type suggestion wasn't specific to this scenario; you can
safely ignore it for now.

On Friday, August 7, 2015, Stefan Scott Alexander <
stefanscottalexx at gmail.com> wrote:

> Thank you Ziv for these 2 very helpful suggestions - they seem to be
> heading in the right direction.
>
> I have incorporated them, and now I'm getting different (but possibly
> "better"?) compiler errors.
>
>
> Suggestion (1)
>
> You provided a reminder of your earlier suggestion to use this pattern:
>
>   <textbox{#Field} id={nid}/>
>   <active code={init nid; return <xml/>}/>
>
> This does seem like a vast improvement over my previous code (which had an
> `onload` event in the <body> tag, which I had simply copied from David
> Patterson's "Democracy Now" example) - since, as you pointed out, the
> `onload` event was probably problematic, because the node in question
> probably didn't exist yet.
>
> I have now changed the code as follows:
>
>   https://github.com/StefanScott/urweb-pikaday/blob/master/pikadayPage.ur
>
> OLD:
>
>   <form onload={init foo_id}>
>     <textbox{#DateField} id={foo_id}/>
>     <submit action={handler}/>
>   </form>
>
> NEW:
>
>   <form>
>     <textbox{#DateField} id={foo_id}/>
>     <active code={init foo_id; return <xml/>}/>
>     <submit action={handler}/>
>   </form>
>
> This now gave the following compile errors:
>
> $ urweb pikadayPage
>
> pikadayPage.ur:27:3: (to 29:12) Error in final record unification
> Can't unify record constructors
> Have:  [Dyn = (), MakeForm = (), Body = ()]
> Need:  [Form = (), Dyn = (), Body = ()]
>
> pikadayPage.ur:27:3: (to 29:12) Stuck unifying these records after
> canceling matching pieces:
> Have:  [MakeForm = ()]
> Need:  [Form = ()]
>
> pikadayPage.ur:28:3: (to 29:12) Error in final record unification
> Can't unify record constructors
> Have:  <UNIF:U526::{Unit}> ++ [Form = ()]
> Need:  [Dyn = (), MakeForm = (), Body = ()]
>
> pikadayPage.ur:28:3: (to 29:12) Stuck unifying these records after
> canceling matching pieces:
> Have:  ([Form = ()]) ++ <UNIF:U526::{Unit}>
> Need:  [Dyn = (), MakeForm = (), Body = ()]
>
> $
>
> Well... It looks like the compiler is *almost* happy - if the only
> conflict now remaining is between a MakeForm field and a Form field.
>
> However, I do not know what these two fields mean, or where they come
> from, so I don't know how to attempt to resolve this compile error.
>
>
> Suggestion (2):
>
> I haven't yet tried creating a wrapper function (like `activate` in
> Logitext) in accordance with your second suggestion - but after (ie, in
> addition to) doing suggestion (1) above, I did also try making a quick
> change to the result type in pikadayControl.urs - changing it from
> `transaction unit` to `transaction xbody`:
>
>
> https://github.com/StefanScott/urweb-pikaday/blob/master/pikadayControl.urs
>
> OLD:
>
> val init :
>   id ->
>   transaction unit
>
> NEW:
>
> val init :
>   id ->
>   transaction xbody
>
> I was expecting that this might actually compile, since it seemed that the
> new "result type" `transaction xbody` might be more appropriate for use in
> the <active> tag added in Suggestion (1):
>
>   <active code={init foo_id; return <xml/>}/>
>
> However, this gave a different (but possibly also helpful?) compile error:
>
> $ urweb pikadayPage
>
> pikadayPage.ur:27:24: (to 27:54) Unification failure
>
> Expression:
> fn _ : {} =>
>  return [<UNIF:U458::Type -> Type>]
>   [xml <UNIF:U460::{Unit}> <UNIF:U461::{Type}> ([])] _
>   (Basis.cdata [<UNIF:U460::{Unit}>] [<UNIF:U461::{Type}>] "")
>
> Have con:
> {} ->
>  <UNIF:U458::Type -> Type>
>   (xml <UNIF:U460::{Unit}> <UNIF:U461::{Type}> ([]))
>
> Need con:
> (xml ([Dyn = (), MakeForm = (), Body = ()]) ([]) ([])) ->
>  transaction <UNIF:U453::Type>
>
> Incompatible constructors
> Have:  {}
> Need:  xml ([Dyn = (), MakeForm = (), Body = ()]) ([]) ([])
>
> $
>
> This error message seems somewhat similar to the previous error message.
> It seems to be saying that there is some incompatibility among the
> following pieces:
>
> (a) the "result type" of function `init` as declared in file
> pikadayControl.urs
>
> (b) the "result type" of the curly-bracketed expression in the tag:
>
>   <active code={init foo_id; return <xml/>}/>
>
> (c) possibly also the "result type" being returned by the JavaScript
> `init` function as defined in pikadayControl.js
>
>
> The JavaScript `init` function:
>
> By the way, here is the JavaScript function `init`:
>
> https://github.com/StefanScott/urweb-pikaday/blob/master/pikadayControl.js
>
> function init ( nodeId ) = {
>   var picker = new Pikaday ( {
>     field: document.getElementById(nodeId),
>     firstDay: 1,
>     minDate: new Date('2000-01-01'),
>     maxDate: new Date('2020-12-31'),
>     yearRange: [2000,2020]
>   } ) ;
> }
>
> It is a slight modification of the JavaScript provided in the Pikaday demo:
>
>   http://dbushell.github.io/Pikaday/
>
> Thiss JavaScript function appears to take an argument `nodeId`, and
> creates a `new Pikaday` attached to that node, assigning the result to a
> variable called `picker`
>
> I don't *think* this JavaScript `init` function actually returns anything:
> apparently the `var picker` is merely a "throwaway" (?) and the function is
> being run simply for its side-effect (attaching the `new Pikaday` to the
> node `nodeId`)?
>
> This makes me wonder if the "result type" of this `init` function (in
> JavaScript) might also dictate the "result type" of its corresponding
> Ur/Web FFI declaration (which was previously `transaction unit` and is now
> `transaction xbody`).
>
>
> Remarks:
>
> The compile error messages are providing intriguing clues about these
> interdependencies between the various pieces.
>
> However, I don't yet have enough experience in this area to be able to
> have a truly "deterministic" methodology for writing this stuff - I'm
> simply using trial and error, throwing various syntaxes at the compiler and
> trying to decipher the error messages.
>
> Thanks for any further help!
>
> ###
>
>
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