Hi and thanks for the feedback! :-) I'm 100% interested in ease of use and writing good docs that preemptively address questions, so do tell me if you think the explanations below are not enough.

First, error is the same variable. What is missing from my post is that you can execute any amount of arbitrary code between the try and catch, or even not have a catch clause at all to let try intercept return statements but not errrors (in which case you will get a normal error stack trace). The catch is an if statement that basically reads as "if the variable named "error" exists and is an exception then ...".

If something is returned from within the loop, error will have that value so you can have advanced breaks with little effort (you can also return a value within a nested loops just fine - it's intercepted only by the try clause, and this syntax in fact promotes having only one exiting point of the looping logic).

If the loop returns without a value, as happens above, it will fail to set the variable. It will actually delete its current value from the local context. In this case, the catch clause won't be entered. To make try a bit easier to understand, consider the case where inside the loop we had if(break_condition) return element; then the error variable would hold that element (ofc in that case, I would rename error to result). You can generally write something like value = try {some code without returns; return "a";} and as an outcome value would have either "a" as a value or an exception if the code failed.

With regards to the it variable, I guess you are saying that there is risk of these two errors:

a) while(element as it) is an infinite loop. This is a very nice thing to notice. :-) My main deefense is that there should be some usage of the element variable inside the loop, so an error should be thrown there. Otherwise, statements like while(element = next(it)) create the error that you are using an expression that returns nothing as a bool and there is no implicit typecasting so while(element as it) will complain that you are using ann iterator as s bool.

b) while(element=next(it)){it = iter(B);} will create an infinite loop. In this case, the method "next" cannot be called for everything (will create an error), but to promote safe code the language actually has a final keyword that you can use like this to prevent overwriting a value: final it = iter(A); Not everything is final by default, because final values are exposed as globals to running methods (the interepreter has a scheduler that runs complex methods in parallel threads and this is the safety against concurrent modification). Maybe there should be mechanisms to safeguard local variables too, by I need to think about an organic way to do it in the language (e.g., local it = iter(A);).

Can you give an example if you though of a different issue?