I appreciate your detailed answer, but I don't understand the distinction - it feels almost like a form of solipsism to me. Say I'm a traveler exploring the p

I appreciate your detailed answer, but I don't understand the distinction - it feels almost like a form of solipsism to me. Say I'm a traveler exploring the programming language universe, and I land on a programming language planet. I wish to determine whether said planet has functions that "you can call in order to get a string from stdin", or whether it "sets up the dominoes in an elaborate arrangement" and "lets the runtime system knock them down". What experiment could I perform? What program could I write that would illustrate the difference?