Hello! > The first token in a YieldStatement production is always preceded by one of > these separator tokens: ;, {, }, ), or ->.
Seems I'm missing something. Could you please illustrate in which case YieldStatement could be preceded by ')'? Also what about '->'? In lambda '->' is followed by an expression or block, but not a statement. In switch '->' is followed by block, throw or expression plus semicolon. Also could YieldStatement be preceded by ':' in old switch format? E.g. System.out.println(switch(0) { default: yield 1; }); // seems legit Also sections 16.1.7 and 16.1.8 are named identically. Probably there's some mistake. With best regards, Tagir Valeev. On Fri, May 24, 2019 at 7:25 PM Gavin Bierman <gavin.bier...@oracle.com> wrote: > > A draft spec including the compromise strategy below is available at: > > http://cr.openjdk.java.net/~gbierman/jep354-jls-20190524.html > > Comments welcomed! > Gavin > > On 22 May 2019, at 17:45, Brian Goetz <brian.go...@oracle.com> wrote: > > We’ve been drilling into the spec and implementation of yield as a contextual > keyword. We have three possible strategies, all of which are specifiable and > implementable, but with tradeoffs. > > The “dumb strategy” would be to say that `yield` is a keyword when it appears > in the first position of a statement production (e.g., after an open brace or > a semicolon.). This is simple to spec, and simple to implement, but it > doesn’t so do well with variables named `yield`: > > yield++; > yield = 3; > if (foo) > yield += 3; > yield[3] = 4; > > The “smart strategy” says that `yield` is a keyword only within the context > of the YieldStatement production; the rest of the time it is an identifier. > This is also simple to spec, and does the right thing in all unambiguous > cases, but requires unbounded lookahead, which compiler implementations may > not like. The one ambiguous case is > > yield(e) > > which would match both YieldStatement and ExpressionStatement, and here we > bias towards YieldStatement. Naked yield() invocations can qualify the > invocation: > > this.yield(3) > Thread.yield(4) > > The “compromise” strategy is like the smart strategy, except that it trades > fixed lookahead for missing a few more method invocation cases. Here, we > look at the tokens that follow the identifier yield, and use those to > determine whether to classify yield as a keyword or identifier. (We’d choose > identifier if it is an assignment op (=, +=, etc), left-bracket, dot, and a > few others, plus a few two-token sequences (e.g., ++ and then semicolon), > which is lookahead(2). > > The main difference between the compromise strategy and the smart strategy is > the handling of method invocations that are not unary: > > yield(3, 4) > > In the smart strategy, we’d figure out that this is a method call; in the > compromise strategy, we’d require qualification just as we do with the unary > method. > > The compromise strategy misses some cases we could parse unambiguously, but > also offers a simpler user model: always qualify invocations of methods > called yield when used as expression statements. And it offers the better > lookup behavior, which will make life easier for IDEs. > > So my recommendation here is the compromise strategy. > > On May 21, 2019, at 10:50 AM, Tagir Valeev <amae...@gmail.com> wrote: > > I discussed this with colleagues and can confirm that for IntelliJ > IDEA parser it will be no problem to always consider yield as a > statement. At least it's much easier than to consider it as a > statement inside switchy blocks only. > > With best regards, > Tagir Valeev. > > On Tue, May 21, 2019 at 12:38 PM Tagir Valeev <amae...@gmail.com> wrote: > > > So does this (option B plus your No) mean that IDEs would tend to color > "yield" as a keyword (at the beginning of a statement) even if followed by > "("? > > > My "No" was mostly against options C and D where symbol resolution > affects the parse tree. Sorry if it wasn't clear from my message. When > the context for the parsing is available inside the same Java file, > it's usually ok. See the 'var' restricted keyword: > > var var = 10; // first is highlighted as type, second as local variable > var = 20; // var is highlighted as local variable, despite it's at the > beginning of a statement. > var(1); // var is highlighted as a method call, despite it's at the > beginning of a statement. > > We have no very big problems parsing this. > > With best regards, > Tagir Valeev. > > On Tue, May 21, 2019 at 2:52 AM John Rose <john.r.r...@oracle.com> wrote: > > > On May 20, 2019, at 8:24 AM, Tagir Valeev <amae...@gmail.com> wrote: > > > Assuming that we agreed on 'yield' the option B seems the most attractive. A > big No to context-specific parse tree. It's a complete pain to IDEs. Don't > forget that IDE often deals with incomplete code, missing dependencies, etc., > and still needs to provide reasonable highlighting and completion. Imagine > that 'yield' method is available via import static Foo.* or superclass. In > this case we don't want to look into other files to build a correct parse > tree. > > > So does this (option B plus your No) mean that IDEs would > tend to color "yield" as a keyword (at the beginning of a > statement) even if followed by "("? > > I suppose that would work. It's hard to predict what that > would feel like, but it's logical. > > — John > > >