[mikelevins]

All the time. Constantly. Often enough that when I was using a Scheme that compiles to the JVM, I wound up in extended conversations with the compiler's author about how to add such features to his compiler. It was possible to do, and he was interested in doing it, but it was really too much work to be practical.

The context matters, though. I've been working with Lisp systems (and occasionally with Smalltalk systems) for over thirty years, and the way I normally work is to start with some simple sketch of a model and some simple interactions with it, and build it up gradually, interactively. While my program runs, of course.

That means making a lot of incremental changes to the model as I go, which, in a class-based system, means a lot of changes to classes. And since I prefer to modify my work while it runs, that means a lot cases of the environment saying, "hey, this definition changed; what do you want to do about it?"

If you typically work in an environment that doesn't support those kinds of incremental changes to a running system, then of course you're going to learn a way of working where such situations don't come up, because they can't.