> If you're doing 100% agentic development, that advantage disappears<p>I beg to differ. Turns out, Lisp REPL - an actual, "true" REPL, not something like Python's (which is not the same), is an enormous multiplier for agentic workflows.<p>a) Lisp code can be very terse yet retain its readability - it never becomes cryptic like APL. Therefore, it's more token efficient. It was actually proven that Clojure is one of the most token-efficient "mainstreamish" PLs. <a href="https://martinalderson.com/posts/which-programming-languages-are-most-token-efficient/" rel="nofollow">https://martinalderson.com/posts/which-programming-languages...</a><p>b) When you give an LLM a closed loop system where it can evaluate code in a live REPL and observe the results, it stops guessing and starts reasoning empirically. Instead of predicting what code will do, it can run it, read the output, adjust, and iterate - the same way a skilled human developer works. Incremental evaluation of forms maps naturally to how an LLM generates tokens.<p>This isn't some theoretical hand-waving - I experience it every day - my WM on Mac is yabai that gets controlled via Hammerspoon, which uses Lua, which means I can use Fennel, which means I can use Lisp REPL. I would give the LLM a task, something to do with my app windows - it connects to the live REPL and starts analyzing, prototyping and poking into things interactively.<p>All my custom MCPs are written in babashka (Clojure) <a href="https://github.com/agzam/death-contraptions" rel="nofollow">https://github.com/agzam/death-contraptions</a> - whenever there's a problem or I need to improve my AI harness, LLM just does it from "inside out" and it takes less time and fewer tokens.<p>My main editor is Emacs - LLM can fully control it. I can make it change virtually any aspect of it. To load-test the MCP that does that, I made it play Tetris in Emacs. And not just to run it, but to play it for real - without losing. It was insane.<p>And of course, day-to-day I have to deal with non-Lispy, non-homoiconic languages more. And to be honest (even though of course I'm biased in this) static type systems is the exact thing in practice where their advantages feel like stop making any big difference. While Lisp REPL feels far more useful.