We have a few helper functions that take in an array of thunks/chunks and return promises. They work well, but with the async/await syntax, i’m not able to inline it like I was hoping i’d be able to. It’s not a huge deal, because you can create a new function as a work around, but I thought i’d show you an example. The async tag is ommitted from the javascript compiled code and is a run time error even though in rescript everything compiles correctly.
Broken code w/ run time exception:
let doThings = (chunks: array<unit => promise<'a>>): promise<array<'a>> => {
chunks->Array.map(c => c())->Js.Promise2.all
}
let run = async () => {
doThings(
["0", "1"]->Js.Array2.map(async number => {
async () => {
Js.log2("number in here!", number)
await Js.Promise2.resolve()
Js.log("more going on.....")
}
}),
)
}
run()
The focus is this part: async () => {. You’d expect the JS outputted code to have the async flag as well, but instead this is what the compiled code looks like:
// Generated by ReScript, PLEASE EDIT WITH CARE
'use strict';
var Curry = require("rescript/lib/js/curry.js");
var Belt_Array = require("rescript/lib/js/belt_Array.js");
function doThings(chunks) {
return Promise.all(Belt_Array.map(chunks, (function (c) {
return Curry._1(c, undefined);
})));
}
async function run(param) {
return doThings([
"0",
"1"
].map(function (number) {
return function (param) {
console.log("number in here!", number);
await Promise.resolve(undefined);
console.log("more going on.....");
};
}));
}
run(undefined);
exports.doThings = doThings;
exports.run = run;
/* Not a pure module */
You can see right here: return function (param) { it’s missing the flag async, which would be like: return async function (param) {. It was strange since rescript was compiling and everything seemed to have worked.
Anyways, the workaround is simply breaking it out into it’s own function like so:
let doThings = (chunks: array<unit => promise<'a>>): promise<array<'a>> => {
chunks->Array.map(c => c())->Js.Promise2.all
}
let handleInside = async number => {
Js.log2("number in here!", number)
await Js.Promise2.resolve()
Js.log("more going on.....")
}
let run = async () => {
doThings(
["0", "1"]->Js.Array2.map(number => {
() => handleInside(number)
}),
)
}
run()
This then compiles correctly and everything works. Here is the compiled code:
// Generated by ReScript, PLEASE EDIT WITH CARE
'use strict';
var Curry = require("rescript/lib/js/curry.js");
var Belt_Array = require("rescript/lib/js/belt_Array.js");
function doThings(chunks) {
return Promise.all(Belt_Array.map(chunks, (function (c) {
return Curry._1(c, undefined);
})));
}
async function handleInside(number) {
console.log("number in here!", number);
await Promise.resolve(undefined);
console.log("more going on.....");
}
async function run(param) {
return doThings([
"0",
"1"
].map(function (number) {
return function (param) {
return handleInside(number);
};
}));
}
run(undefined);
exports.doThings = doThings;
exports.handleInside = handleInside;
exports.run = run;
/* Not a pure module */
Anyways, not a huge deal, but I figured I should share this in case any one runs into this problem, or someone would like to fix the problem.
Thank you!
