RWO does an excellent job in introducing OCaml's main features in a simple and pragmatic way. It really does show the strength of the language and demonstrates the building blocks one can use to write high quality software.
One aspect that I think could be explored deeper is how to architecture complex applications with the language. How the module system can be used to build abstractions and protocols for not-trivial systems? For example how one could build a database with it, or even an operating system? I'm in the process of learning OCaml and what is really difficult for me is to understand what are the most idiomatic and efficient ways of modelling application domains. Although there are many open-source projects one can learn from (like JaneStreet's libraries, Nymote sub-projects, etc), the concepts and practices they use are sometimes hard to understand just reading the source.
I was just about to suggest looking at projects like Mirage/Irmin et al but since you mention Nymote, I assume you've already found your way to them.
If it helps, we have a series of blog posts about some of the recent library releases on the Mirage blog [1], some of which go into the design of those libraries. Perhaps they'd be useful?
Thank you! I'm impressed with the serie of blog posts the Mirage team posted lately – really informative and inspiring. I think this kind of system design articles are really valuable to actually learn how to use the language in the wild.
Another good example of a very good software design reading I've fuond is the OCamlgraph's paper[1], which demonstrates the strength of the ML's module system in a not trivial situation.
One aspect that I think could be explored deeper is how to architecture complex applications with the language. How the module system can be used to build abstractions and protocols for not-trivial systems? For example how one could build a database with it, or even an operating system? I'm in the process of learning OCaml and what is really difficult for me is to understand what are the most idiomatic and efficient ways of modelling application domains. Although there are many open-source projects one can learn from (like JaneStreet's libraries, Nymote sub-projects, etc), the concepts and practices they use are sometimes hard to understand just reading the source.