Guess the language by the error

Ok, can we pass a function that consumes items instead of returning an Iterator?

error[E0666]: nested `impl Trait` is not allowed
   --> src/main.rs:103:63
    |
103 |    fn scan<T>(&mut self, z: T, mut f: impl FnMut(HeapElement, impl std::io::Read, T) -> T) -> std::io::Result<T> {
    |                                       ------------------------^^^^^^^^^^^^^^^^^^---------
    |                                       |                       |
    |                                       |                       nested `impl Trait` here
    |                                       outer `impl Trait`

Computer says "no".