[fiddlerwoaroof]

In Common Lisp, classes are mostly specialization tags so you don't have to redefine them all that much. However, being able to redefine your functions and other code on the fly is amazing (i.e. make a request to a REST endpoint, get an exception in the debugger, modify and reload just a couple functions and then restart the request handler without ever going back to the browser/Postman and re-issuing the request)

[fiddlerwoaroof]

Also, little story: once I had to migrate a large database between an old, schemaless, version of a product to a new one that enforced schemas. Because the old version was schemaless, there was a whole host of minor schema issues. For various reasons the migration process already involved a Python script spawning an older version of Python and communicating with it over a pipe. I started running the migration and it failed 20 minutes in, so I fixed the issue and restarted the migration only for it to fail differently 20 minutes in. At this point I wrote some code to catch the exception, spawn a prompt that let me input the appropriate conversion code that got evaled and added to a dictionary of translators, along with a function to determine if the conversion applied. This way, every 20 minutes or so I’d come across a new form of corruption and add a translator to fix it without restarting the whole process.

When I learned CL, the condition/restart system and pervasive hot code reloading reminded me of my Python hack and how much easier it would have been in a language designed for this sort of programming.