[Dn_Ab]

OCaml doesn't so much make monads invisible (except for a technical yet handwavy note on semicolons just as true for C) as make them unnecessary due to being more pragmatic. It's strict and allows mutability when necessary. Of course explicitly recognizing when you're using a monad is extemely powerful and allows elegant formulations of lots of wonderful things like LogicT, probabilistic computation and continuations.

Specific instances of monads are definable in most languages in use today, it's when you want to generalize over monads that Haskell stands out. For that you want higher kindedness, Ocaml can simulate them using the module system but it's rather cumbersome. There is a work around described here: https://ocamllabs.github.io/higher/lightweight-higher-kinded.... The work around is also applicable to the cousin, F#: https://github.com/palladin/Higher/tree/master/src/Higher.Co...