I mostly skimmed the article but isn’t he basically talking about Lisp and the REPL? He dis mention Smalltalk but i’m pretty sure it adopted the interactivity from Lisps.
You don't get instant live update of existing variables in a REPL. The programming paradigm described is called Reactive Functional, it's the model popularized by spreadsheets.
However, spreadsheets can't create new objects programatically; new libraries for web development (React, Vue.js) are popularizing the model, but so far they're using reactive components just for high-level components, not the whole line-by-line program execution. Bret Victor's "Learnable Programming" concept (linked at the end) shows how you could apply the approach to a whole textual program.
