@jvlk/rescript-future - Functional Futures for ReScript

I usually stay away from directly interacting with Promises or async/await syntax and use Futures or Tasks instead. In JS/TS land I use fluture or fp-ts for this. There are bindings for libraries that already exist and some older ReScript implementations, but I wanted something lightweight that had an API that was focused on usage in ReScript v11 with the Core library.

Here’s an example.

let _ =
  ->Future.flatMap(res => {
    switch res->Webapi.Fetch.Response.ok {
    | true => Ok(res)
    | false =>
      Error(`${res->Fetch.Response.status->Int.toString}: ${res->Fetch.Response.statusText}`)
  ->Future.map(res => res->Fetch.Response.statusText)
  ->Future.fold(Console.error, Console.log)

A future will never throw an error, even if the promise call does. It gets caught and returned as an Error.

Here’s an example of cancelling a future in React.

let make = () => {
  let request = Future.fetch("http://httpstat.us/200?sleep=1000")
      onClick={_ => {
        request->Future.reset // reset the future to make sure the Abort Controller is new
        let _ = request->Future.fold(Console.error, Console.log)
      onClick={_ => {
        let _ = request->Future.cancel // Aborts the fetch request and stops any processing of the response

I’m happy with the API and error handling so far. Now I am looking into a way to cancel a Future.

Did you check GitHub - bloodyowl/rescript-future: Cancellable futures for ReScript? It has cancellation.

Other than that, great work! We definitely need more of those v11-ready packages. Maybe we need a way to rank them (for uncurried and other things) in the package index?


I did check it out, yes. I’m using the way it handles cancellation as an inspiration.

1 Like

Cancellation is working and docs are in decent shape with a few basic examples.

Published an rc to npm: @jvlk/rescript-future - npm

I’m gonna do some dog fooding with an app I am working on to sort out any kinks before I ship v1 for real.


Ok, v1.0.0 is published!