I agree that an AP2 system, which is what we are discussing, should not have a method named .fulfill for the reasons you state. A promise which, at the AP2.flatMap level is "accepted" or "adopted" is, at the AP2.then level "resolved". I suggest the method in question be called .resolve, that it accept, not recursively unwrap/flatten/assimilate at all. The AP2.flatMap programmer will understand .resolve as accepting. The AP2.then programmer will understand .resolve as resolving.
On Mon, Aug 19, 2013 at 6:34 PM, Domenic Denicola < [email protected]> wrote: > Mark, I completely agree with you. However, I think this somewhat ignores > the issue of this thread. The problem with AP2, even completely ignoring > `flatMap`, comes when you consider the behavior of the `Promise.fulfill` > method. Namely, what does this code do? > > ```js > var foreverPending = new Promise(() => {}); > var p = Promise.fulfill(foreverPending); > ``` > > Because the recursive unwrapping has moved to the `then` side, we have that > > ```js > p.then(() => console.log("this will never be called")); > ``` > > Such a promise `p` *cannot* be called fulfilled, if its fulfillment > handler will never be called. From existing Promises/A+ definitions, it is > resolved, but pending. Yet it was returned by `Promise.fulfill`, making > that method a lie. > > One could answer by saying that you should ignore `Promise.fulfill` (and > the resolver's `fulfill` callback), and this would be justifiable. Indeed, > just like `flatMap`, I expect `fulfill` to be ignored by Promises/A+ and > the broader community of promise users. But it prevents a severe > pedagogical difficulty, because on the one hand, we are telling people that > the fundamental states of a promise are fulfilled, rejected, and pending, > whereas on the other hand we are saying that `Promise.fulfill` is a broken, > mis-named method that should never be used even if you want to produce a > fulfilled promise. (Or rather, especially not then!) > > As to your message, I guess it is unclear to me whether you envision > `Promise.fulfill` as part of the eventual TC39 consensus. Even if you > don't, as of now it's part of the DOM folks design, and I was hoping to > stop a mistake there as well. > > -- Cheers, --MarkM
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