Ask HN: Interaction programming

What would programming process and languages look like if the only way to reflect on a piece of code would be to interact with it? No interfaces, no objects. Sure, message passing, but without knowledge of what's on the other end nor what it likes to receive. Sort of like rumor-exploration framework. My thinking is to send test messages to explore, to reply with informative messages to test requests. But those are just example, primitive cases.