for sure! #uxn also encourages you to consider whether to check the exit condition at the start of the loop (as you've done here) or at the end after the first iteration (replacing the final jump with a JCN).

it's definitely a different way of thing from what i was used to.

there's many ways to build loop-like things, I think, the next step would be to pass the width and height of the rect through the stack, that will reveal a lot of interesting things about stack machines.