Add promises

[hayd]

Move deferred from util/ to promises/.

Add delay and timeout promises.

cc @ry @keroxp #188 (also denoland/deno#1800 #201 etc.)

Note: This would also need promises to be added to the registry: https://github.com/denoland/registry/pull/57

I am sure there are several other useful promise constructs, but these were the first that came to mind.

[ry]

What else is going to go into promises?

Can you explain why you're against "util"?

[hayd]

Perhaps a pool implementation (which I have) and likely some other helpers (see e.g. bluebird).

util is not descriptive... at all. IMOT util is a blight (everything's a util 😭 ), naming is really important (and difficult), likely we'll refactor in the future but nevertheless we should make a best effort.

Helpers for promises, as well as for generators (ala itertools), are things that should be in std. I remember there was an issue somewhere to discuss what would be in std - but I can't find it.

[keroxp]

I have neutral opinion about util. But I don't strongly oppose util module set.
A problem we have to decide at now is how should small modules be placed on. Those modules are usually difficult to be classified.

There are some different solutions:

• 1. treating every single small module as a top level module set (like //deferred/mod.ts)
• 2. create util module set and move them into util (//util/deferred.ts)
• 3. create new module sets for them and strictly classify it (//promises/deferred.ts)

I don't agree with 1, and 3 may become difficult to manage as time goes by.
I'm sure 2 is not best solution but possible one at this time.
There are no plan to use promises or promise for other promise-related modules.

I respect @ry 's decision for this repository. We have to make some decision on #130 together.

And by this case, I'm also concerned about usage of deno_std's namespace in deno.land/x/. I will open another issue...

[hayd]

An argument could be made for dropping all the independent std modules in the registry, i.e. reference std solely under /x/std/... I'm not sure about that. (Though it would solve the relative/not found issue.)

This PR is independent of #130. There's certainly more promise-related helpers that could be included to /promises/ (I added a couple already and have some follow up ideas), I don't think anything is gained by having deferred in its own file in this case.

There is a larger question/issue: what else should be in std?

[ry]

I think we ought to remove Deno.land/x/http and other sub modules of std... I will do some work on this today.
I very much agree with @keroxp’s position in these org discussions.

[j-f1]

Could these two lines be combined?

Suggested change

	super(message);
	super(`Timeout after ${ms}ms`);

Also, should this use something like Node’s ms utility to display the elapsed time in a more friendly manner?

[hayd]

@ry should this also be in individual files: promises/deferred.ts promises/timeout.ts promises/delay.ts ??

[ry]

This one is out of date - if you want to land this still - let's discuss on gitter

[hayd]

@ry defer is useful (and already used in several projects) and would be good to add back to std somewhere, as are the others...

Happy to re-land this, but want to know how you want it structured.

should this also be in individual files: promises/deferred.ts promises/timeout.ts promises/delay.ts