Based on the introduction, that looks like a great book which I definitely wouldn't have found on my own, so thanks for the suggestion! I'll have to give it a try when I have some time.

I have some more older links, ocaml changed a bit over time, but I think they are still relevant:

https://caml.inria.fr/pub/docs/oreilly-book/html/index.html

https://caml.inria.fr/pub/docs/u3-ocaml/

https://ocaml.github.io/ocamlunix/