I've never understood this. You can't just combine the state of an old program with new code, without lots of weird things potentially happening. The algorithms and all intermediate products would have to match, at every step of the programs.

That’s why working with lisp feels like touching alien tech - it works, it’s designed for that exact workflow.

(It’s also essentially pointless when your unit of deployment is a disposable container and not a long running lisp system, but it at least makes development a bit nicer)