That's how Smalltalk worked in the 70s (or Squeak for a modern dialect). You can edit any part of the running system and it takes effect right away. One classic

That's how Smalltalk worked in the 70s (or Squeak for a modern dialect). You can edit any part of the running system and it takes effect right away. One classic example is redefining "true" to "false" and watching the system grind to a halt. Genera was similar for LISP machines in the 80s, you had full access to the code and could modify it on the fly. Ironically one reason that always comes up when people here talk about why Smalltalk never took off is that it's hard to integrate with source code control systems like git that are file-based.