You could have invented Fenwick trees

Written by Brent Yorgey — I'll definitely give it a read when I have time. When I was learning Haskell, I found his Typeclassopedia [1] to be the best explanation of Monads, Monoids, Applicative and such. His pedagogical approach was delightful in contrast to all the "monad is like a burrito" tutorials.

[1] https://wiki.haskell.org/wikiupload/e/e9/Typeclassopedia.pdf