> async/await is also available in a bunch of other languages, including F#, C#8, Haskell[...]

Haskell (GHC) does not provide async/await but uses a green thread model.

kaoD 5 days ago | parent | next [-]

Aren't green threads and async-await orthogonal concepts?

As I understand it async-await is syntax sugar to write a state machine for cooperative multitasking. Green "threads" are threads implemented in user code that might or might not use OS threads. E.g.:

- You can use Rust tokio::task (green threads) with a manually coded Future with no async-await sugar, which might or might not be parallelized depending on the Tokio runtime it's running on.

- ...or with a Future returned by an async block, which allows async-await syntax.

- You can have a Future created by an async function call and poll it manually from an OS thread.

- Node has async-await syntax to express concurrency but it has no parallelism at all since it is single-threaded. I think no green threads either (neither parallel or not) since Promises are stackless?

Is this a new usage of the term I don't know about? What does it mean? Or did I misinterpret the "but"?

As a non-Haskeller I guess it doesn't need explicit async-await syntax because there might be some way to express the same concept with monads?

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valcron1000 5 days ago | parent [-]

You don't need "monads" (in plural) since GHC provides a runtime where threads are not 1:1 OS threads but rather are managed at the user level, similar to what you have in Go. You can implement async/await as a library though [1]

[1] https://www.cambridge.org/core/services/aop-cambridge-core/c...

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kaoD 3 days ago | parent [-]

What do you mean with "in plural"?

	▲	valcron1000 2 days ago \| parent [-]
		In the sense that you only need to work with the standard IO monad to get the benefits of the runtime.

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Yoric 5 days ago | parent | prev | next [-]

(author here)

Well, I haven't used Haskell in a few years, so I could absolutely be wrong. That being said, I'm almost sure that I saw a presentation by Simon Marlowe 15-20 years ago demonstrating GHC with a multicore scheduler (alongside `seq` and `par`). Also, from the very same Simon Marlowe, there's a package called `async` https://hackage.haskell.org/package/async which basically provides async (no await, though).

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LtWorf 5 days ago | parent | prev [-]

How are green threads implemented?

	▲	whatevaa 5 days ago \| parent [-]
		A runtime with it's own scheduling. Something rust doesn't want to require.