ES7 `async`/`await` implementation with concise syntax#836

summivox · 2016-02-01T05:16:59Z

ES7 async/await is a syntax sugar for promise+generator async control pattern. Although this feature is still a draft in even ES7, it has gained considerable traction, and is completely usable right now through a babel plugin.

This patch provides a concrete example on which we can discuss syntax extensions to LiveScript that compiles to ES7 async/await.

`async function`

Append an additional > to all arrows: ->>, ~>>, -->>, ~~>>
Rationale for the syntax: terseness
Prepend keyword async to arglist of arrow functions: async (arglist) -> body
Rationale for the syntax: agrees with strawman proposal on async "ES6 rocket" functions (redundant)
Prepend keyword async to named function definitions: async function name(arglist)
Rationale for the syntax: obvious

`await` expression

await compiles to await (in the same way as how yield is compiled now)
await all compiles to await* (in the same way as how yield from is compiled now)
Rationale: await* is proposed to have the same semantics as Promise.all (see strawman) (no longer in standard)

Example

af1 = (x) ->> await x
af2 = async (a, b, c) ~> await @x
async function af3(x)
  a = await af1 x

compiles to

var af1, af2, this$ = this;
af1 = async function(x){
  return (await x);
};
af2 = async function(a, b, c){
  return (await this$.x);
};
async function af3(x){
  var a;
  return a = (await af1(x));
}

References

Official Strawman Proposal
Example of async/await usage
Babel plugins for transpiling ES7 async/await to ES5
Promise Generators #752 Using backcalls with Promises #754 : prior art
So-called "next big version" #811 : LiveScript "2.0" checklist

dead-claudia · 2016-02-16T06:12:17Z

How would that work with libraries using that identifier? I'm working on one that could implement this general functionality at the library level, possibly more optimally than engines could. (I'm using Bluebird-style shortcuts to do it, including keeping the stack minimized.)

summivox · 2016-02-16T06:57:14Z

['ID', 'async'] is left alone unless it is followed by a PARAM( or FUNCTION

summivox · 2016-02-16T07:01:24Z

@vendethiel decided in #752 that lsc should not transpile ES7/ES6

darky · 2016-10-25T19:57:41Z

async/await almost in v8 as stable feature. Any activity here?

dead-claudia · 2016-10-25T20:03:37Z

@gkz? IIRC this barely missed the V8 train for Node 7, and it's been shipping in Edge for a while.

summivox · 2016-10-25T20:34:01Z

My opinion:

I don't think the syntax and semantics of async/await in ES7 would change in any major way, now that it is being rolled out experimentally.
The proposed syntax for LSC does not conflict with existing code, and is intended for early adopters specifically targeting ES7 (and quite possibly including further transpiling toolchain)

Therefore I believe it is safe for this to land in LSC.

dead-claudia · 2016-10-25T20:38:43Z

WRT the PR itself, I feel having both (arg) ->> (and friends) and async (arg) -> is rather redundant.

dead-claudia · 2016-10-25T20:39:02Z

@summivox You mean ES8? It barely missed the ES7 train.

summivox · 2016-10-25T21:00:36Z

@isiahmeadows It seems that people have stopped caring about the "version number" and started to rely on shipping schedule instead. I'm fine with this ;)

Regarding syntax: Historically coffee-ish languages have this dilemma of symbols vs English words. && vs and in LSC is a prime example --- different operator precedence (with and being more sane therefore the default). I don't see why both versions of arrows cannot co-exist. However, if only one is to stay, I would suggest ->> which stays in line with the "symbolic" feel of the arrows while retaining orthogonality, and async function for the "English" side.

dead-claudia · 2016-10-25T21:56:18Z

There is a push to get rid of many of the duplicate operators like && vs
and in one of the issues here. I can't remember the number right off,
though.

On Tue, Oct 25, 2016, 17:00 Yin Zhong notifications@github.com wrote:

@isiahmeadows https://github.com/isiahmeadows It seems that people have
stopped caring about the "version number" and started to rely on shipping
schedule instead. I'm fine with this ;)

Regarding syntax: Historically coffee-ish languages have this dilemma of
symbols vs English words. && vs and in LSC is a prime example --- different
operator precedence (with and being more sane therefore the default). I
don't see why both versions of arrows cannot co-exist. However, if only one
is to stay, I would suggest ->> which stays in line with the "symbolic"
feel of the arrows while retaining orthogonality, and async function for
the "English" side.

—
You are receiving this because you were mentioned.

Reply to this email directly, view it on GitHub
#836 (comment), or mute
the thread
https://github.com/notifications/unsubscribe-auth/AERrBIhK8Lb0Von9c7bB-0p91_TBKyrPks5q3m35gaJpZM4HQRZq
.

summivox · 2016-12-25T02:30:47Z

I just tested this with node v7.3.0 . It feels awesome.

@isiahmeadows : I agree with you on removing async (args) -> body now. For anonymous functions, LSC allows only arrows while ES6 allows both function() and arrow. There is no good reason to keep an alternative syntax for async.

dk00 · 2017-02-02T11:39:31Z

await* have been removed from the proposal, should we remove it as well, or simply compile it to await promise.all ... ?

gkovacs · 2017-03-30T09:35:20Z

Thank you for this excellent patch. I have noticed a bug when using it against the master branch ( 47ad4eb )

getdict = (name) ->>
  data = await getCollection(name)
  return {[key, val] for {key, val} in data}

somehow gets compiled to (notice the superfluous yield*)

// Generated by LiveScript 1.5.0
(function(){
  var getdict, out$ = typeof exports != 'undefined' && exports || this;
  out$.getdict = getdict = async function(name){
    var data, key, val;
    data = (await getCollection(name));
    return (yield* (function*(){
      var i$, ref$, len$, ref1$, resultObj$ = {};
      for (i$ = 0, len$ = (ref$ = data).length; i$ < len$; ++i$) {
        ref1$ = ref$[i$], key = ref1$.key, val = ref1$.val;
        resultObj$[key] = val;
      }
      return resultObj$;
    }()));
  };
}).call(this);

summivox · 2017-03-30T09:37:46Z

@gkovacs : this is a separate issue: #764 #938

gkovacs · 2017-03-30T09:45:38Z

Thank you for the fast response! Also here's another issue. The following code compiles:

foo = -> ''

a = foo(async ->
  ''
)

And so does this:

foo = -> ''

a = foo ->>
  ''

But the following does not:

foo = -> ''

a = foo async ->
  ''

So in the example above, ->> and async -> aren't quite identical.

dead-claudia · 2017-03-30T10:00:18Z

Here's my proposed resolution: remove async -> altogether. It doesn't fit with every other anonymous function syntax.

I'm kind of 1% tied to this project now, since the parser bugs have pretty much killed this project for me, and no stable release yet has provided ES6 support. But that's a little more meta.

summivox · 2017-03-30T10:00:48Z

I want to remove async -> syntax so this is a wontfix.
I just haven't been actively working on this project for a long time.

see http://wiki.ecmascript.org/doku.php?id=strawman:async_functions async function: `->>`, `~>>`, `-->>`, `~~>>`, `async (arglist) ->...`, `async function name (arglist)` await: `await` => `await`; `await all` => `await*` (proposed to translate to `Promise.all`, not final) backcall does NOT work, but this should be fine because they were invented to create the illusion of async function anyway

summivox · 2017-03-30T10:07:49Z

Hmm done.

gkovacs · 2017-03-30T22:46:31Z

I fixed the issue of yield* statements being generated inside async functions due to bug #764 in gkovacs/livescript-async@97b86df (also removed await all as await* is no longer part of ES2017)

yizhong-ms · 2017-03-30T22:48:56Z

@gkovacs could you please make a PR to my branch; thanks

… being generated inside async functions

gkovacs · 2017-05-25T22:44:34Z

@yizhong-ms @summivox created a PR to your branch at https://github.com/summivox/LiveScript/pull/2/files

removed await* which no longer exists. fix issue of yield* statements…

determin1st · 2017-05-27T23:15:08Z

does this update work? tried to run examples on livescript.net with no luck.

dead-claudia · 2017-05-28T02:21:28Z

@determin1st This PR hasn't been merged, and livescript.net isn't updated until the next release IIRC.

determin1st · 2017-05-28T03:18:52Z

oh, i see. experimented with promises a little, found it useful but they are not "real" part of the language. it's like helpers. probably wont use this functionality.

gkovacs · 2017-07-14T20:27:39Z

@rhendric Given that the ES2017 standard (with async functions) has now been released and nodejs and all major browsers support the syntax by default, is there any chance you could review and merge this pull request? Thank you!

rhendric · 2017-07-14T20:33:43Z

I would be very happy to look it over! @summivox, can you confirm that this is in a state that you endorse for merging, or if there are any outstanding issues or design questions, summarize what they are?

summivox · 2017-07-14T20:36:26Z

@rhendric Let me quickly build and verify. I think tests need to be added.

rhendric · 2017-07-14T20:39:52Z

Yes please to tests. No rush from me (I'm actually running out the door right now and probably won't have free time for a few days anyway); just drop me a mention when you're ready for a review and I'll follow up when I'm able. Thanks!

willin · 2017-08-27T17:54:10Z

mark, pls add in asap

willin · 2017-08-29T03:57:35Z

can it use now?

gkovacs · 2017-08-29T04:01:00Z

@willin If you're impatient and want to use it now do npm install -g livescript-async ( https://www.npmjs.com/package/livescript-async - it is just standard livescript plus this patch, uploaded by me to NPM as I grew impatient for this to be released). But no it is not yet released in the official livescript.

willin · 2017-08-29T04:06:12Z

it will be great helpful if you add a documentation for this package.

ozra · 2017-09-19T20:10:11Z

@gkovacs - thanks for the npm! Trying it out right now.

gkovacs · 2017-09-20T06:42:05Z

I've added tests in a new pull request #978 - as summivox asked this to be taken over in #977 I will be taking over the efforts for getting this merged

rhendric · 2017-09-21T05:02:00Z

#978 has landed, so I'm closing this.

summivox force-pushed the async-await-concise branch from 226cb80 to 11d17fc Compare February 1, 2016 16:21

summivox changed the title ~~ES7 async/await implentation with concise syntax~~ ES7 async/await implementation with concise syntax Feb 7, 2016

summivox force-pushed the async-await-concise branch from 11d17fc to ba94ce4 Compare June 9, 2016 01:29

summivox force-pushed the async-await-concise branch from ba94ce4 to 8854954 Compare June 17, 2016 17:56

summivox mentioned this pull request Feb 1, 2017

Please add supports to "async await" keywords #683

Closed

dk00 mentioned this pull request Feb 2, 2017

support Async/Await livescript/discuss#2

Open

gkovacs mentioned this pull request Mar 16, 2017

mark function explicitly as async? dk00/livescript-next#2

Closed

summivox force-pushed the async-await-concise branch from 8854954 to 4b9323f Compare March 30, 2017 10:06

summivox added 2 commits March 30, 2017 03:07

remove async ->

ed71900

summivox force-pushed the async-await-concise branch from 4b9323f to ed71900 Compare March 30, 2017 10:07

removed await* which no longer exists. fix issue of yield* statements…

da454db

… being generated inside async functions

gkovacs mentioned this pull request May 25, 2017

removed await* which no longer exists. fix issue of yield* statements… summivox/LiveScript#2

Merged

Merge pull request #2 from gkovacs/async-await-concise

eebd7b1

removed await* which no longer exists. fix issue of yield* statements…

vendethiel mentioned this pull request Sep 19, 2017

Status on async / await straight through compilation? #977

Closed

gkovacs mentioned this pull request Sep 20, 2017

ES7 async/await implementation with concise syntax, plus tests #978

Closed

rhendric closed this Sep 21, 2017

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summivox commented Feb 1, 2016 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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async function

await expression

Example

References

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`async function`

`await` expression

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