On May 12, 2019, at 12:38 PM, Brian Goetz <brian.go...@oracle.com> wrote: > > Digression: What’s so terrible about “return”, any why is it OK for lambdas > but not OK for switches?
Although I like Lisp (block foo … (return-from foo x) …), I buy your argument that "unwind the current call frame" is different enough from "transfer control within the current call frame", enough to merit syntactic difference. There's a very subtle difference in Java (but not in Lisp) between call frames and blocks which you didn't mention directly but which tips the balance for me: A Java call frame has side-effectable locals (because Java is an imperative language, as you said). Thus, a block which exits to the current call frame can also push side effects to that call frame, while a block that unwinds to a different call frame cannot push side effects to enclosing variable bindings, because they will be in a different call frame. That's a difference that is usually ignored when reasoning about Java programs, thanks to the implicitly final rule. Using distinct syntaxes for same-frame block exits and different-frame unwinds adds a little extra help to programmers to keep track of the difference. It doesn't matter that programmers usually don't care about the difference; having a syntax difference might help them avoid surprise errors, and allow them to keep the semantic differences at a non-distracting subliminal level. Thus, if I have to say "return" I know I can't return an extra value by side effects, since all my up-level variables will be final (implicitly or not). And if I say "yield" I know I can return an extra value, if I need to, by punching it into some visible local.
