Since OCaml 4.08, OCaml has added convenient syntax for working with monads and applicative functors.

Binding operators were introduced to offer convenient syntax for working with monads and applicative functors; for those, we propose conventions using operators * and + respectively. They may be used for other purposes, but one should keep in mind that each new unfamiliar notation introduced makes programs harder to understand for non-experts. We expect that new conventions will be developed over time on other families of operator.

https://ocaml.org/manual/5.2/bindingops.html

I would like to extend this page to add a few simple examples of special let bindings as well as a link to the appropriate page in the OCaml documentation.

Note that at the moment the current official "informal" documentation for OCaml at https://ocaml.org/docs/monads just links back to this textbook, so this page is likely the primary reference for monads in OCaml that most people will find when searching.