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Re: Futures

From: David Sheets <kosmo.zb@gmail.com>
Date: Tue, 23 Apr 2013 19:25:48 +0100
Message-ID: <CAAWM5Typ_1WnH3UfT5Nx9-BY=hpD6WB9pA79TFOdyCae2Qh1vQ@mail.gmail.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: David Bruant <bruant.d@gmail.com>, Dean Landolt <dean@deanlandolt.com>, Brendan Eich <brendan@mozilla.com>, "Mark S. Miller" <erights@google.com>, Douglas Crockford <douglas@crockford.com>, "public-script-coord@w3.org" <public-script-coord@w3.org>, Norbert Lindenberg <w3@norbertlindenberg.com>, Markus Lanthaler <markus.lanthaler@gmx.net>, EcmaScript <es-discuss@mozilla.org>
On Tue, Apr 23, 2013 at 7:02 PM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
> On Tue, Apr 23, 2013 at 6:12 AM, David Bruant <bruant.d@gmail.com> wrote:
>> Anyway, my point was that there exist libraries in which "then" is a
>> function and the object with this function isn't a promise. These libraries
>> will end up in a terrible confusion when used with Futures.
>> You think you're resolving a future with an object and... oops! the built-in
>> Future algorithm confused your object for a promise. Suddenly, not only are
>> you not resolving your promise with the value, but your .then method is
>> called unexpectedly.
>
> Agreed.  I'll note, though, that if the semantics of .resolve() are
> non-recursive (it strips off one layer of promise/future, but no
> further), then this becomes somewhat less of an issue, as it can be
> worked around - if you want to return something that's not a promise,
> just wrap it in a fulfilled promise (via some sugar function - I've
> proposed such in www-dom).  That wrapper will be unwrapped straight
> away, and the future accepted with the value within.

<http://lists.w3.org/Archives/Public/www-dom/2013AprJun/0051.html>?
Future.of == "monadic return"? Doesn't seem too sugary...

> The big problem only arrives if you both treat all thenables as
> promises/futures, *and* have recursive resolve semantics, because then
> you can't *ever* return a non-promise with a .then() method.
>
> I'd prefer that resolve only strip away a branded future, not an
> arbitrary thenable, and for there to be a way to brand a thenable as a
> future.  That way, using other-library promises just requires one trip
> through the branding function and they can interoperate.  Existing
> libraries tend to expose the same mechanism already, so that the
> other-library promises expose all the proper methods of the "main"
> library.
>
> But I want non-recursive resolve *more*, and if I was forced to choose
> one, would take monadic resolve over branded futures.

"non-recursive resolve" == "monadic run" == "comonadic extract"?
"recursive resolve" == "monadic run" compose { fixpoint of "monadic join" }?

Will Futures be associative and have left and right identity between
bind ("then") and return ("of")? Will this be specified explicitly?

If libraries are able to create Future-like objects that interoperate
with built-in Futures, will they be required (ha) to satisfy these
equivalences (associativity, identity)?

Thanks,

David
Received on Tuesday, 23 April 2013 18:27:15 UTC

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