How to exit a promise from within a promise?

Question

How do I exit a promise from within a promise? The perl6 docs do not provide an easy method. For example:

my $x = start {
    loop { # loop forever until "quit" is seen
        my $y = prompt("Say something: ");
        if $y ~~ / quit / { 
            # I want to exit the promise from here; 
            # "break" and "this.break" are not defined;
            # "return" does not break the promise;
            # I do NOT want an error exception when exiting a promise;
            # I want to return a value as the result of this promise;
        }
        else { say $y; }
    }
}

I do not want to be in the promise loop forever. break() and this.break() are not recognized, and return does not break the promise.

Answer 1

Use the last keyword to quit the loop.

The kept value of a start block is the value returned by its last statement.

So:

my $x = start {
    loop { # loop forever until "quit" is seen
        my $y = prompt("Say something: ");
        if $y ~~ / quit / {
            last 
        }
        else { say $y; }
    }
    42 # <-- The promise will be kept with value `42`
}