Using & between patterns is unfortunate given that if if first pattern is not total and does not match, we will not "execute" the second pattern. So the semantics is lazy but currently '&' means non-lazy on expressions.
While I understand the discomfort that drives you to make this observation, I think we should be a little more careful with our terms; lazy is not the right word here. (When used this way, *ALL* patterns are lazy! A pattern is not an expression; it is not "evaluated" like expressions are. It is a _recipe_ for a deferred computation (like a lambda.))
When we say `x instanceof (P&Q)`, we "construct" the composite pattern P&Q _before we "execute" it_. What are the semantics of such a combined pattern? It is short-circuiting; when we later compute whether a target matches the pattern, we first try to match it to the first subpattern, and if that succeeds, we try to match it to the second subpattern. This is not "lazy evaluation", this is just the semantics of pattern composition with AND. Short-circuiting is a more accurate description here than laziness.
As an analogy, imagine we had intersection types in instanceof (we already do for casts, so this is not much of a leap). If we asked `x instanceof T&U`, and x was not an instanceof T, would we insist that we also test against U (which could throw if the JVM can't find U.class to load!) Or would we accept that a test against the intersection type T&U can reasonably "short circuit" the test if it fails the first one? Of course we would. Why is it different for patterns, which are a generalization of this kind of test?
Continuing on the "like a lambda" analogy, if pattern refers to variables in the current scope as one of its "inputs", this is like a capturing lambda. And, like a lambda, when we were looking at `true(e)`, we said that any locals in `e` should be effectively final.
So to propagate that constraint into the current model: in a guarded pattern P&&g, all locals referred to in `g` should be effectively final. (We've already said this of pattern input parameters in general.)
