And now, how do you break from within the 2nd and 3rd level of nesting? break can only break one of them. If only "break" had a label, so you could say "break toplevel;" instead of just "break;" (and name the relevant scope "toplevel", of course).
Turns out, you actually can! instead of "break toplevel;", you just write "goto toplevel;". There's another minor change, in that you have to put the name at the end of the scope, rather than the beginning of the scope, which is why people tend to name it after the next block (e.g. "goto cleanup;" in this case).
I was only replying to your "here's error handling without goto". And I'm not implying that it is impossible - just that your solution does not scale as is to more than one level of scoping.
There is nothing that absolutely needs goto (including error handling), because Turing completeness does not require goto. so you might wait forever; I'm not sure what it is that you guys are arguing about with respect to state machines.
(of note, I keep waiting for TCO proponents to show me an example in which the guarantee of TCO in scheme makes the world so-much-better. The claim always comes up, and every example I've seen so far requires at most adding two more lines in Python, and no adding of TCO)
Turns out, you actually can! instead of "break toplevel;", you just write "goto toplevel;". There's another minor change, in that you have to put the name at the end of the scope, rather than the beginning of the scope, which is why people tend to name it after the next block (e.g. "goto cleanup;" in this case).