Clarify how Variables work

[davidspies]

In the documentation for Variable::set, (https://docs.rs/differential-dataflow/0.11.0/differential_dataflow/operators/iterate/struct.Variable.html#method.set) it says "Adds a new source of data to the Variable." but doesn't anywhere clarify what it means for a Variable to have a source or for that matter what happens when you add one. Is it concatenating or overwriting?

Also I'm confused about what exactly "iterative" does. In the example in the book (https://timelydataflow.github.io/differential-dataflow/chapter_2/chapter_2_7.html) it show how to construct the "iterate" function using just a "Variable" and "set". It seems like "iterative" isn't called anywhere. So where is the recursion coming from? Does "Variable::set" do the thing repeatedly or just once?

[isubasinghe]

Yeah variable is confusing tbh.
iterate() just runs the provided function till a fixed point is reached I believe