In Forth we use a data stack and the functions (in Forth, Words) and each function interprets the stack according to its definition.
The Word + takes 2 values off the stack, adds them a puts the sum on top of the stack.
Forth words are defined by what's expected on the stack, the word name and what's left on the stack. It's possible to spec a whole program without actually writing new code (you start with your Forth and extend it. That spec can be given to competent programmers who can split the job of filling it all in.
All that and it's OOP too!