michael@0: // set.iterator() is live: entries added during iteration are visited.
michael@0: 
michael@0: var set = Set([5]);
michael@0: var log = '';
michael@0: for (let x of set) {
michael@0:     log += x + ';';
michael@0:     if (x > 0)
michael@0:         set.add(x - 1);
michael@0: }
michael@0: assertEq(log, '5;4;3;2;1;0;');
michael@0: assertEq(set.size, 6);