How long will rescript support async/await?

[Mng12345]

It is very painful for me to write asynchronous code with Promise in rescript. Does the core team consider adding async/await support in rescript, and when?
The code is just like a piece of shit, and hard to understand and review

[tom-sherman]

There are a couple of threads about this

A proposal for async style sugar

Hi all, I made a draft of proposal for async style syntactic sugar, it is available here: Draft: Programmable let async for continue passing style in ReScript - Google Docs Note this is in pretty early stages, similar to stage 1 in ES proposals, but technical discussions are welcome

Alternate async/await proposal

This proposal is a possible alternative to A proposal for async style sugar. The syntax and usage of async and await would look very similar to that of JavaScript, e.g. let doSomething = async (arg) => { let value1 = await asyncOp1(arg); ... await asyncOp2(value1); } This would compile to the following JavaScript: let doSomething = async (arg) => { let value1 = await asyncOp1(arg); ... return await asyncOp2(value1); } In order to simplify the implementation, both async and await …

I wouldn’t expect the feature any time soon. If you’re looking for ways to improve your code there are definitely ways to do that don’t involve await; in fact I don’t really see how await would help too much here. The biggest improvement I can see is to replace that big reduce call with a helper that can intersperse an array of promises with a delay.

Something like this maybe:

let {then, thenResolve} = module(Promise)

let delayPromises = (promises, delay) => {
  let rec aux = (promises, resultPromise) =>
    if promises->Js.Array2.length === 0 {
      resultPromise
    } else {
      let head = promises->Js.Array2.unsafe_get(0)
      let rest = promises->Belt.Array.sliceToEnd(1)

      aux(
        rest,
        resultPromise->then(vals =>
          head
          ->then(val => sleep(delay)->thenResolve(() => val))
          ->thenResolve(val => vals->Js.Array2.concat([val]))
        ),
      )
    }

  let head = promises->Js.Array2.unsafe_get(0)
  let rest = promises->Belt.Array.sliceToEnd(1)

  aux(rest, head->thenResolve(val => [val]))
}

let _ =
  stocks
  ->Js.Array2.map(stock =>
    stock->getPrice->thenResolve(price => (price, stock))
  )
  ->delayPromises(250)