Control flow labels

[@FroMage] It has happened to me more than once that I have two interleaved loops and I need to be able to break/continue out of the inner one and I can’t and the resulting code looks terribly messy.

Now, I agree these situations are not super common, so if adding labels as they are in Java is out of the question, I think we can make it work without introducing new syntax and reuse compiler annotations for that:

@read
while(true){
 Integer byte = read();
 if(byte == 2){
   special code that says we need to read 2 more bytes
   for(b in 1..2){
     Integer otherByte = read();
     if(otherByte == -1){
       @read break;
     }
   }
 }
 print("got a byte: ``byte``");
}

I guess that would work, and we can make the typechecker check these labels and the backend should be able to use JVM and JSVM labels.

This is not urgent, but still useful and not intrusive.

[Migrated from ceylon/ceylon-spec#939]

[phlopsi]

Why not simply introduce goto and let us jump out of everything? :trollface:

Joke aside, not being able to get out of multiple loops is kinda annoying. While I do prefer labels, another solution would be to specify a number in the form of break 2; or continue 3; to break out of the first 2 loops or continue from the 3rd loop onwards, respectively.

[RossTate]

Y’all don’t let people break/continue from multiple loops?! I thought y’all wanted a “regular” language!

As for how to do it, annotations seems odd. I don’t really view annotations as critical to code execution; they are annotations onto code. Ceylon does have more heavily integrated annotations, so maybe it makes some sense. Is it that hard to make it part of the syntax?

Also, because this keeps coming up, one related feature request: When a for/while loop is labeled, let me use that label to check whether I’m in the first iteration of the loop. It’d save so much boilerplate.