I would hesitate to call polymorphic variants "part of the OO infrastructure". They are really orthogonal to OO, but they do make OO less necessary. Ironicall

I would hesitate to call polymorphic variants "part of the OO infrastructure". They are really orthogonal to OO, but they do make OO less necessary. Ironically, OCaml has a really nice OO system but it's rarely used because with modules and functors there is little need for it. Put differently, a lot of the conventional use for OO is as a poor man's module system, and when you have a really good module system, you only use OO when you absolutely need the OO kind of polymorphism, and those cases are surprisingly rare (like existential types in Haskell).