This is so old, I personally wouldn't read it. If you want to learn Ocaml, probably the best current resource is Real World Ocaml v2: https://dev.realworldocaml.org/. It doesn't have good coverage of the not so real world things or the myriad of syntax extensions (mostly from Jane Street). The main auther is one of the original co-founders of Jane Street as well. The only reason I'm saying this is that the Jane Streets guys steer the direction of the language heavily, and their needs don't necessarily fit mine. Their standard library alternative Core (which RWO uses) is a ton of code, pulling in hundreds of dependencies. This leads to a native compiled hello world binary being over 20mb.