In Rust, let-else patterns don't allow this, but match guards (used in `match` expressions and the `matches!` macro) can do something like this.

  while matches!(iterator.next(), Some((a, b)) if a + 1 == b) {
      println!("Hello!");
  }

However, using the bound values in an expression is a little harder.

  while match iterator.next() {
      Some((a, b)) if a + 1 == b => {
          println!("{a}, {b}");
          true
      },
      _ => false
  } {}

Since this is a well-formed transformation, it should theoretically be possible to implement this as a macro without changing the language.