This one weird trick allows you to capture loop variables.

[Walter Bright]

On 10/20/2024 3:45 PM, Timon Gehr wrote:
> As someone who has also implemented `opApply`, I do think it is quite 
> straightforward. It's just internal iteration with support for multiple ways to 
> exit the loop, encoded using numerical indices.

That's because you're smarter than I am, Timon. And I'm not joking.

I implemented it as a way to deal with visiting each node of a binary tree. 
Doing that with a range is clunky and unappealing.