Iteration is great but these extra-constructs seem like a unnecessary proliferation of syntactic sugar.

Which is to say, writing a for-loop is two easy lines, why worry about that?

Most of the convenience I see in the code of the OP is a language that can return pairs or N-tuples of values. That's useful for a multitude of things.

If you do operations with vectors that all the same iteration and subscription operations, then one-off errors aren't very likely. One-off/fence-post errors are much more likely when you iterate through a sequence assigned values in more complex or staggered fashion and here an iterator-type isn't going to save you since you have to figure out the logic involved (which you might encapsulate with some object or type or which might have idiosyncratic logic all its own).