I get that. Having read Real World OCaml back when it was an O'Reilly book, I had a hard time not thinking Core was the defacto OCaml std lib. And its horrible documentation made me think the OCaml community was dead - or at least brain-dead. It appealed to one type of learner: Someone who just needs to see type signatures and has no interest in examples of how it could be used.

After reading OCaml From The Very Beginning my stance softened. Learning PURE OCaml is a must. (if you want to do AoC with it). You may find yourself bringing in Core or Base, after you've got a good idea of a solution.

It's definitely a fun language for doing AoC... but it can become extraordinarily frustrating when you hit a wall and all the StackOverflow answers assume Core.