Combine x and y in such a way that x & None = None & x = x. Some(-1) yield x without evaluating y. But Some(x) & Some(y) give None if x != y otherwise Some(x).
Combine x and y in such a way that x & None = None & x = x. Some(-1) yield x without evaluating y. But Some(x) & Some(y) give None if x != y otherwise Some(x).