Forth may not qualify as "modern" for some (though it still has a way of staying around in some contexts, like bootloaders), but it does allow code to store to

Forth may not qualify as "modern" for some (though it still has a way of staying around in some contexts, like bootloaders), but it does allow code to store to and retrieve from the return stack, which is also used for loops. If you read that and thought "does that mean I can change loop iteration order and returns programmatically?!?" and/or "WTF?!", the answer is, yes, to all of it. WTF indeed. I've never actually seen a non-pathological use for this language feature.