He mentioned he liked Common Lisp but they didn't let him use it in production, so he created a Lisp that runs on an industrial runtime.
He'll argue, of course, that the time & effort are worth it for immutable data structures. I'm unconvinced, but that's the great thing: we don't all have to agree! I'm glad he's having fun.
"But Lisp had a bunch of things that needed to be fixed in my opinion. It was built on concretions, you know, a lot of the design of more abstractions and CLOS and stuff like that came after the underpinnings. The underpinnings didn't take advantage of them so if you want polymorphism at the bottom, you have to retrofit it. If you want immutability at the core, you just need to, you need something different to, you know, from the ground up. And that's why Clojure was worth doing as opposed to trying to do Clojure as a library for Common Lisp. The Lisps were functional kind of, mostly by convention. But the other data structures were not, you had to switch gears to go from, you know, assoc with lists to, you know, a proper hash table. And lists are crappy data structures, sorry, they just are. They're very weak, and there's no reason to use them as a fundamental primitive for programming. Also packages and interning were very complex there."
The hierarchy Rich refers to[0] puts domain complexity and misconception as 10× more important than anything that's language specific. I believe this is the basis of the quote I pulled. I think this is compatible with thinking that language features are important, but domain complexity and misconception are more important issues when tackling a problem with code.
[0]: https://github.com/matthiasn/talk-transcripts/blob/master/Hi...