Great, thanks @MatthewDoty!

This is informative. All chippings away are appreciated. I can almost see the co-products. Equational presentation would be great to see. Maybe that would help me to better parse Haskell. I'm more comfortable with the straight mathematical language, and with "ordinary" languages like Python, but when I look at Haskell code it can look blurry.

Another option for these kinds of focussed explanations would be to create small discussions, in the category "Forum Mini-Talks". A wrote a few there. They're not meant to be some kind of earth shaking thing, just to have a useful point that is intended to be made, and to be explained in a way that tries to help the reader get from point A to point B.

Or these approaches could be combined. Answers made in the context of a discussion here could later be culled and organized into a mini-talk.