I was mostly talking about the type level; I certainly didn't mean to imply that Rust didn't have lambdas if that's what you're getting at. But there is no general type of Rust lambdas that take an A and return a B other than the trait object type `dyn impl Fn(A) -> B` (Or FnMut or FnOnce); the concrete type will depend on what variables it captures.

Also, there's a lot of disagreement about exactly what the distinctions between `lambda`, `closure`, `anonymous function` and friends mean. The interpretation of `closure` I'm interested in is basically a bundle of code and data, which can be treated abstractly in a first class way. That could be something that appears as a lambda capturing variables in the text of your program or as an object in a more OO setting which, albeit more verbose for a single function, has a similar level of power of abstraction.

Either way, part of that power is being able to write code that can work with the interface (irrespective of the shape of the enclosed data), and do things like store differing implementations in lists/vecs etc. The only mechanism Rust provides to do that is trait objects.