After using Erlang for a while I became convinced that async anything in interpreted languages is a big design fail. There is a very funny but NSFW (lots of swearing) video bashing node.js along those lines:

https://www.youtube.com/watch?v=bzkRVzciAZg

The author should look into Koka. As I see it, Koka is at the bleeding edge of effect handling, which is why the async Rust team has taken some nibbles of inspiration from it. Alas, Rust as a whole is far too cemented to overhaul everything for generic effect support, but at least it’s been beneficial for async.