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Comment by eru | Hacker News Reader

Interesting!

For comparison, Haskell went with the library approach but has the syntactic sugar of the equivalent of `and_then` built into the language. (I am talking about Monads and do-notation.)

It's a bit like iterating in Python: for-loops are a convenient syntactic sugar to something that can be provided by a library.

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It is a little old, but for the general gist of it, http://aturon.github.io/tech/2018/04/24/async-borrowing/ is an amazing description of the problem here.

It is a PhD level research problem to know if monads and do notation would be able to work in Rust. The people who are most qualified to look into it (incidentally: a lot of the same crew was who was working on async) believe that it may literally be impossible.

My impression is that some of them even burnt out in slog of a supposedly rushed process to land async/await!

Yes, a number of people have suggested introduction of a general do notation (or its analog) instead of usecase-specific async/awayt syntax, but since Rust does not have proper higher kinded types (and some Rust developers say it never will), such proposals have been deemed impractical.

It’s not just HKTs. Figuring out how to handle Fn, FnOnce, FnMut is a whole other can of worms.

I think there were some (related, I think!) proposals here: https://github.com/rust-lang/lang-team/issues/23 https://github.com/rust-lang/rfcs/issues/3000

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