Maybe I'm misunderstanding what you mean by "It began in C#", but F# introduced async about five years before C# 5 was released.

I know it influenced the async await design, but I didn't think it was quite the same. Will go do some reading!

could be wrong about c#, but c# and f# are comes from same parent

async in F# is not a language feature, it’s a library that leverages F# computation expressions (monads).

It’s possible to do async like behaviour in C# using LINQ, so you could argue C# has had the capability (like F#) since LINQ was released.

But, I believe C# was the first mainstream language to implement the async/await method-splitting state-machine (as a language feature)

Async is a special case of continuations. If you have fist class continuations (and monads do notation in practice gives you that), you hardly need async as a language feature.

That's exactly my point. It's not a language feature, it's a library. Haskell, F#, and any other language that supports monads (or as you say, first class continuations), have the ability to do async/await - in a way that appears first-class - but actually is just regular code.

C#, and other languages that have taken the C# approach [to async/await], don't have first class continuations (well, C# does with LINQ, but that compromises most ways the average OO dev works). They implement async/await with first-class keywords that indicate where to slice a method in two.

In my language-ext [1] project I have added the LINQ operators to `Task<T>` which allows C# tasks to be used in the same way that Async is done in F#.

[1] https://github.com/louthy/language-ext/blob/main/LanguageExt...

Do-notation is a language feature though, and that's a superset of async/await.

Incidentally there are papers that are trying to improve on async in C++ by trying to sneak in generalized do-notation.

It began in 1970's with programming languages like Concurrent Pascal.

https://en.wikipedia.org/wiki/Concurrent_Pascal

Simula,

https://en.wikipedia.org/wiki/Simula

And plenty of other ones,

https://en.wikipedia.org/wiki/Coroutine#Implementations

Yes, I remember when my head was blown when I finally understood what this new async/await thing is doing in C#. It was nice to observe other language adopt it with basically the same syntax (Javascript, Python, Hack, then Rust with slightly different syntax). I had some satisfaction that my language got it first

C# really helped to popularized asyc/await as language feature, even though F# had something similar first.