This was the programming model I learned on the lisp machine and Common Lisp: define a few datastructures and some operations on them, explore them with some live data, and expand. All iteratively at the REPL.

A few years later a friend referred to this dismissively as “Programming by successive approximation.”

There is a lot of truth to this, but the distinction isn’t as sharp as it sounds: you still have to think ahead, and as you explore and expand you’ve typically always got something working, some test cases and invariants, and typically you have the benefit of working on live data.

Even though I do most of my work in compiled C++, my work model isn’t that different.