async/await came out of C# (well at least the JS version of it).

There are a bunch of use cases for it outside of implementing concurrency in a single threaded runtime.

Pretty much every GUI toolkit I've ever used was single threaded event loop/GUI updates.

Green threads are a very controversial design choice that even JVM backed out of.

Yep and I loved when C# introduced it. I worked on a system in C# that predated async/await and had to use callbacks to make the asynchronous code work. It was a mess of overnested code and poor exception handling, since once the code did asynchronous work the call stack became disconnected from where the try-catches could take care of them. async/await allowed me to easily make the code read and function like equivalent synchronous code.

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ngruhn 7 hours ago | parent | prev | next [-]

> async/await came out of C# (well at least the JS version of it).

Not sure if inspired by it, but async/await is just like Haskells do-notation, except specialized for one type: Promise/Future. A bit of a shame. Do-notation works for so many more types.

- for lists, it behaves like list-comprehensions.

- for Maybes it behaves like optional chaining.

- and much more...

All other languages pile on extra syntax sugar for that. It's really beautiful that such seemingly unrelated concepts have a common core.

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rafaelmn 7 hours ago | parent [-]

I knew someone was going to bring up monads that's why I put JS version :) JS took the C# syntax.

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WorldMaker 4 hours ago | parent [-]

Similarly F#'s computation expressions predate C#'s syntax, and there is some evidence that C# language designers were looking at F#'s computation expressions. Since the Linq work, C# has been very aware of Monads, and very slow and methodical about how it approaches them. Linq syntax is a subtly compromised computation expression and async/await is a similar compromise.

It's interesting to wonder about the C# world where those things were more unified.

It's also interesting to explore in C# all the existing ways that Linq syntax can be used to work with arbitrary monads and also Task<T> can be abused to use async/await syntax for arbitrary monads. (In JS, it is even easier to bend async/await to arbitrary monads given the rules of a "thenable" are real simple.)

	▲	ngruhn 26 minutes ago \| parent [-]
		> use async/await syntax for arbitrary monads. (In JS, it is even easier to bend async/await to arbitrary monads given the rules of a "thenable" are real simple.) I tried once to hack list comprehensions into JS by abusing async/await. You can monkey patch `then` onto Array and define it as flatMap and IIRC you can indeed await arrays that way, but the outer async function always returns a regular Promise. You can't force it to return an instance of the patched Array type.

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Ygg2 8 hours ago | parent | prev [-]

> Green threads are a very controversial design choice that even JVM backed out of.

Did they? Project Loom has stabilized around Java 21, no?

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voidifremoved 7 hours ago | parent | next [-]

Virtual Threads aren't quite the same as green threads (they don't block the OS thread) and they work extremely well now.

	▲	gf000 3 hours ago \| parent [-]
		They are not even remotely the same, there is no reason to compare them at all.

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rafaelmn 7 hours ago | parent | prev [-]

I stand corrected, I stopped keeping track of JVM years ago, was referring to initial green threads implementation.