Yes I was thinking of something like that. Only I wish I could also know whether I is first and/or last without calling into the iterated structure. I know this

Yes I was thinking of something like that. Only I wish I could also know whether I is first and/or last without calling into the iterated structure. I know this looks like corner case syntactic sugar but it comes up a lot, e.g. when serializing to JSON. I guess I should write my own iterators but I want them everywhere...