Operators and functions are effectively the same thing, yeah. In CS we normally mean #4 though ... which can technically be thought of as a variation of #3 pas

Operators and functions are effectively the same thing, yeah. In CS we normally mean #4 though ... which can technically be thought of as a variation of #3 passing/returning "the whole universe" as an argument (and including the actual arguments in the implicit lambda capture), but thinking like that only makes sense for functional programmers.