I think the GP meant polymorphism. Rust traits being static ad hoc polymorphism. I thought it was possible, though, to achieve the same thing with Functors. Just the standard library deliberately didn't and chose to have things like 'print_int', 'print_string' and so on instead of a Print Functor.
Yes functors would be the way in OCaml, but there's no implicit context resolution that implicitly resolves such symbols within a Functor the way you can in Rust or Haskell. This missing implicit context resolution makes for bad ergonomics, particularly for any kind of numerical code, which tend to be the very first kinds of things that new programmers try in a new language. "Hey, why do I need to use + in one case and +. in another? This is dumb, OCaml is not a serious language."
In OCaml the integer operations are implemented using LEA instructions, and the floats are boxed. The language is not really suitable for numerical code...
