Async plan?

[osa1]

I'm curious what the plan is for implementing async support in the current version of Koka? I found #384, but it was created a year ago and last updated 7 months ago. Is this on hold? Can we expect async libraries any time soon?

[TimWhiting]

Hi @osa1, I'm the author of that PR and am in touch with Daan. There are a few things with the type system & implicits, as well as better low level bytes / string primitives that it seems like he wants to do prior to finishing the LibUV integration. The branch should be still useable, but lacks HTTP/S support (only TCP + UDP / file support currently).

Also of interest is probably Daan's response here, in which he talks a bit more about his plans.

In the unofficial community libraries I have copied some of the JS backend part of the async support in the PR (which doesn't need any language / runtime changes).
Here is an example of how to use it.
Add the -i../path/to/std after cloning to use the community std library.

That library also has more examples of how to use Koka's extern functions - C/JS ffi, which you can use to bring other async functions you are missing if you are willing to write some native code. (Which I'm assuming you are comfortable with seeing as you work on Dart).

If you have more questions with regards to those repositories in general the Koka enthusiasts have been conversing on Discord: https://discord.gg/CEkHHnTqEv

Daan has been busy recently with mimalloc (a memory allocator) which he works on for microsoft research and which has recently been adopted by Python for memory allocation, so that has demanded a lot of his time, but we are meeting soon to discuss next priorities.

[TimWhiting]

Ahh, I forgot there is an error in the std null library which is used by async.kk (it should work with the dev branch of Koka - or with a simple change to null.kk).

Your command is correct.

Go to home/omer/Downloads/koka/share/koka/v3.1.2/lib/std/os/null.kk and change the last definition to the following:

// Cast a boolean `False` to null
pub fun bool/null( b : bool ) : null<()>
    if b then Just(()).null else Nothing.null

Then recompile as you did before:
koka --target=js test.kk -i../std

And finally run the .mjs file using node xx.mjs

[TimWhiting]

BTW, I also just updated the koka-community/std repo with a temporary std/async/null.kk file with this change, and updated std/async to depend on that so you can use it without messing with the packaged std libraries. You'll just need to pull the latest commit.

[osa1]

Thanks, it works now.

[osa1]

@TimWhiting I'm trying to find where is the await function used here is defined: https://github.com/koka-community/std/blob/f98bee331da917569a28c0cfb331d40484632275/std/async/async.kk#L426-L430

The only await definition that I could find is here:

koka/lib/std/os/task.kk

Lines 41 to 42 in 21089c1

	pub fun await( p : promise<a> ) : pure a
	unsafe_await( p.promise )

But it calls a C function:

koka/lib/std/os/task.kk

Lines 26 to 27 in 21089c1

	noinline extern unsafe_await( p : any ) : pure a
	c "kk_promise_get"

So it can't be used in JS backend. How is async defined in the JS backend?

[TimWhiting]

It's a bit hidden by the comment above it, but it is just two definitions down: https://github.com/koka-community/std/blob/f98bee331da917569a28c0cfb331d40484632275/std/async/async.kk#L443.

To drill down to the native code / effect:

• https://github.com/koka-community/std/blob/f98bee331da917569a28c0cfb331d40484632275/std/async/async.kk#L473
• https://github.com/koka-community/std/blob/f98bee331da917569a28c0cfb331d40484632275/std/async/async.kk#L574
• https://github.com/koka-community/std/blob/f98bee331da917569a28c0cfb331d40484632275/std/async/async.kk#L547
• Though the closest handler could also be a cancelable scope or interleaved async computations which mostly just forward the async handling to the main async handler
• https://github.com/koka-community/std/blob/f98bee331da917569a28c0cfb331d40484632275/std/async/async.kk#L380
• https://github.com/koka-community/std/blob/f98bee331da917569a28c0cfb331d40484632275/std/async/async.kk#L528

Note that there is not really a need for any native code to be involved except if a computation wants to yield or wait early. Those functions use implicits to require that the platform provide set-timeout equivalent functions to schedule a callback on the event loop. These are defined in https://github.com/koka-community/std/blob/main/std/async/timer.kk, and exposed along with async here: https://github.com/koka-community/std/blob/main/std/async.kk.

Also, note that I just took the async support from the version 1 std libraries and updated it to use the new keywords, etc.
https://github.com/koka-lang/koka/tree/dev/lib/v1/std