What the hell is Reactive Programming anyway?

A reflection on defining reactive programming, moving away from implementation-focused definitions (streams, async, event emitters) toward a more fundamental one: the declarative expression of relationships between values that change over time. The concept traces back to 1969 with spreadsheet-like systems and hardware description languages. The conclusion is that reactive programming is essentially a flavor of declarative programming, and distinctions between push/pull, signals/streams, or sync/async are implementation details rather than defining criteria of the paradigm.