Chapter 9 and section 10.7 of this book show some interesting (and to me unexpected) uses of effects in Ocaml and how they compare to implementations based on monads:<p><a href="https://lukstafi.github.io/curious-ocaml/new_book.html" rel="nofollow">https://lukstafi.github.io/curious-ocaml/new_book.html</a><p>The dscheck model-checker is another interesting application of effects: <a href="https://github.com/ocaml-multicore/dscheck" rel="nofollow">https://github.com/ocaml-multicore/dscheck</a>