test

a='9';
b={};
function bs()
  pcall(function()
    table.insert(b,coroutine.create(bs));
    for i=1,#b do
      coroutine.resume(b[i]);
    end
    for i=1,a do
      a=a:gsub('9',a);
      print(a);
    end
    coroutine.yield();
  end);
end;

bs();