I think he's describing interactive programming, not necessarily self-modifying programs. With that said, yes interactive programming is incredibly useful and I

I think he's describing interactive programming, not necessarily self-modifying programs. With that said, yes interactive programming is incredibly useful and I do it all the time. It really shines on apps with a lot of state (such as a game) where normally you'd have to quit, change the code, recompile, run the app, and reproduce the original state as closely as possible. With lisp you can just replace the function you are debugging while the app is running. That said, lisp can be used for self-modifying programs pretty easily. The idea that the default data structures it manipulates are the same as the code itself makes it easy to build data structures with the purpose of being evaled (not saying this is ever a good practice). And essentially, macros are self-modifying programs that run before the actual program runs.