async / await keywords

[Former user]

It would really awesome if DWScript could support for async functions. Await and Async are just syntactic sugar for working with promises. It would be cool if we can define a async method like:

// define procedure as async function
  procedure main: async;

procedure main;
begin
  await Sleep(5000);
  console.log('A after 5s');
  await Sleep(3000);
  console.log('B after 3s');
end;

the compiler emits this

function main() {
   (async function(){(null);
   await Sleep(5000);
   console.log("A after 5s");
   await Sleep(3000);
   console.log("B after 3s");
   })();
};

Yeah, we need to to wrap it inside an async function and add "await" before the method "Sleep" to work in synchrounous manner.

[Toky Olivier Razanakotonarivo]

Are async/await syntaxes now supported please?

[Toky Olivier Razanakotonarivo]

I think that it's better to have like this for normal procedure/function:

Procedure MyProc; async;

And for anonymous function/procedure:

OneProc(async function())...

@Eric Grange What do you propose please waiting that this feature will be implemented? Thank you.

[Toky Olivier Razanakotonarivo]

Hello,

Nice that you finally implemented it. Thank you.

Regards,

[Eric Grange]

This is currently very minimalistic support to “play” with the syntax.

Currently it’s with async in front (as in JS) but without having any effect on the return value of the function or procedure, and the compiler knows nothing about promises or async execution context.

A snippet inspired from the MDN doc where this can be used is below.
I had a look at making Promises into generics, but truth is JS libs out there would run afoul of the strong typing of a generic… So maybe a named Variant + helpers could be preferable, less strict but still providing some degree of syntax checking and auto-completion.

type
   TPromiseExecuteResult = procedure (execute : procedure (result : Variant));

type
   Promise = class external 'Promise'
      constructor Create(p : TPromiseExecuteResult);
   end;
function setTimeout(p : procedure; millisecs : Integer) : Integer; external;

function ResolveAfter2Seconds : Promise;
begin
   Result := new Promise(
      lambda (resolve : procedure(r : Variant))
         setTimeout(lambda resolve('resolved') end, 2000);
      end
   );
end;

async procedure asyncCall;
begin
  PrintLn('calling');
  var result := await ResolveAfter2Seconds();
  PrintLn(result);
  // expected output: "resolved"
end;

asyncCall();

‌

[Toky Olivier Razanakotonarivo]

Hello @Eric Grange,

Thank you. I will try it.

Thank you for your support.

Regards,

Toky

[Jon-Lennart Aasenden]

Great work as always eric! This makes DWScript generated JS highly compatible with existing frameworks, and also makes it possible to write some very powerful and exciting libraries.

Thank you!