Great Kata. Although I have had zero prior experience with Haskell, type families, datakinds, and GADTs -- whatever that may be -- I find this instructive, enjoyable, and somewhat challenging. This is a great introduction to the basics of mathematical logic. You need only to read between the lines, get the gist of what you're looking at, draw the picture in your head, and voila. Easy 2 kyu kata.

I love the simplicity. Taking notes.

I'd highly suggest using just "while(n)" rather than"while(n!=0)" since every integers except 0 counts as 'true'.