I agree that actor languages are the purest form of OOP as Alan Kay has expressed it. And unlike Smalltalk, Erlang just accepts that some things are naturally functions, not messages.
Erlang's Joe Armstrong and Alan Kay did a talk/interview together:
Smalltalk has no problem at all with accepting that some things are naturally functions: it has always had blocks! The call operator is `value`, not `()`, but it's the same "apply a piece of code to some values" operation.