Comment by chrismorgan

Conditions are certainly technically fascinating. I was introduced to them back when Rust used them for I/O error handling. But Rust ~0.8 dropped conditions, because people found them much more confusing than Result<T, E>-based error handling, and almost no one was actually using any of the power of conditions.

Broadly speaking, conditions can be implemented as a library feature, so you can reintroduce such things in cases where the extra functionality is compelling (though now users won’t be familiar with it, so it’ll be much harder to justify).

Other programming languages have been tending in the direction of implementing generators and async/await, which can be used to more smoothly implement some of the key concepts of conditions. (They’re not the same by any means, but related.)