[usrusr]

That's essentially what the "copy formula down the entire column, updating relative references as you go" pattern of Excel abuse does, right? Might be quite interesting to have a UI that takes all the tedious and distracting column-filling from your shoulders but keeps the tabular representation for debug/understanding.

[TuringTest]

Yes, that's how it is done in a spreadsheet.

A stream allows you to generalice the computation, not depending on the number of data items that were available when you defined the function; i.e. not different from a function with a loop.

Applications like AirTable and other modern outliners are exploring interfaces to model that kind of generalized data tables and relations with visual metaphors.