Recently I've been teaching myself new programming languages with books. I got one for D, Elixir, Erlang, and Go.
OCaml was also on my list of languages to learn, but there is no good OCaml book available. I started reading an online course textbook (for Cornell's CS 3110), only to find it painfully slow, beginner-level, and aimed at course tools besides. Eventually, I found the official OCaml manual to be the best source of information.
Unforunately, there is no published version of the manual. It is available online as HTML, PDF, or even a text file, but that's all. So, I went to Lulu and published my own copy of their PDF.
The PDF is so long I split it into two volumes. I'm pleased by how the manual turned out, though I haven't actually used it much for reference -- I've already spent two weeks programming OCaml before it arrived (Lulu is not fast).
I've been working on a terminal text editor in OCaml for two weeks. I'll post about that in more detail if and when I finish it.