Rust

Yeah, they could literally have the same syntax as now, but w/ let when introducing a variable. So:

match (left.next(), right.next()) {
    (Some(let l), Some(let r)) => {}
    (Some(let l), None) => {}
    (None, Some(let l)) => {}
    (None, None) => {}
}

Or you could put the let before the Some(...) as let Some(l), which allows us to keep the current if let Some(...) = ... syntax. Either of those would feel more consistent than the current implementation.