To be fair, the article mentions reading via which elements are 'full', and I mention by the 'crease point'.
When I started parachuting, I struggled to quickly read windsocks, because the definition of 'full' can be somewhat ambiguous (Is it mostly / somewhat / completely inflated, what if it's full now but wasn't three seconds ago..)
I'd found: See where it 'breaks' provided a much better point of reference.
Perhaps this will help others that shared my confusion :)
That's a quite unobvious consequence of the software progress. Making software be "a bunch of bricks for creating applications" do come with costs. And the main cost is performance.
As I see on the demo, it evaluates the expression itself. There is a ton of possibilities to misinterpret the domain of operations involved. Moreover, how should we control the details to which it should unwind the undergoing calculations?
That way of work seems a bit too optimistic to me.
Jupyter, and ultimately Python, evaluates the expressions. handcalcs just displays the resulting information with variable values from the Python locals dict.