It's very common for me to revisit Common Lisp code I wrote 20 years ago because it still works and I've forgotten what algorithm I used. Within a couple of min

It's very common for me to revisit Common Lisp code I wrote 20 years ago because it still works and I've forgotten what algorithm I used. Within a couple of minutes I have one of two reactions: "Hey that was pretty clever" or "I get how this works but this coding style is idiotic." Usually the latter. So yeah, I can glance at a Common Lisp program and tell pretty quickly what it's doing. That comes from studying 10,000 Common Lisp programs. It's pattern recognition.