This is a wonderful exploration further into the original spirit of that comment and very much reflects the experience that I have had as well. The only other

This is a wonderful exploration further into the original spirit of that comment and very much reflects the experience that I have had as well. The only other runtime I have found that has a similar absence of pain is Emacs (though Emacs has its own separate warts unrelated to friction at the repl). I think there is a deeper disconnect between having something that looks like a repl and a real repl which is that for decades Emacs didn't even have a command line style repl, because the repl was everywhere, hidden behind C-x C-e or M-:. A point of confusion I think is that repl in the lisp world has come to imply much more than that somewhere there is some code that looks like (loop (print (eval (read)))). That level of sophistication of the repl concept was archaic well before common lisp, but the term continued to be used and evolved to signify a runtime that could support interactive development. For many of the other languages the issue isn't with the form of the interface (almost any language can have a prompt, come up with printed representations that can round trip through their printed representation, etc.) it is that their underlying runtime can't support the kind of redefinition that is needed to avoid the creeping insanity that can arise when code becomes subtly out of sync with data e.g. in Python classes and instances. Computers are faster now, so the workaround is "restart the runtime" and users hardly notice. Therefore no one bothered to implement what common lisp has. Given how long a cold boot took back in the 70s and 80s, avoiding the restart at all cost was a top engineering priority. Lisps evolved in a significantly different and harsher selective environment than many of the runtimes that came after, and as a result had to solve certain fundamental problems that are practically invisible for users today. In the time since I wrote the referenced comment on reddit I have also discovered the amazing power of save-lisp-or-die. At the time it hadn't quite clicked for me. I'm guessing that the author has had a similar experience given the title of the series so I'm looking forward to reading more in the future! In the mean time I also learned a bit of docker, and what I find amusing/sad about it is that slad is basically docker without all the fuss. Sure it can't bring a whole unix system with it, but it is a couple of orders of magnitude smaller and significantly less complex.