What exactly are you arguing for? Closures can be implemented using closure conversion as a derived form in most languages. That's how you compile the code in t

What exactly are you arguing for? Closures can be implemented using closure conversion as a derived form in most languages. That's how you compile the code in the first place... The point is that you reason about closures as ordinary functions with local assumptions. You don't need to know how they are implemented at all. On the other hand, in Rust you need to be aware of the implementation in order to use higher-order functions effectively.