Fermin gave an interesting talk to the 2023 EmacsConf. The title of the talk was The Emacsen family, the design of an Emacs and the importance of Lisp. He starts with the premise that Lisp is the right language for Emacs implementation and extension.
That takes him to Elisp. It was, he says, a pretty nice language when Stallman designed it and today it’s still “good enough”. But that brings up the question, “Why not Common Lisp?” As we all know, RMS is not a fan but there’s more to it. When Emacs was being developed, a final specification was still 10 years away and there weren’t any (or at least any “free”) implementations available so RMS rolled his own.
But, Fermin says, we can do much better today with Common Lisp. In particular, the SBCL implementation is fast, compiles to native code, and is stable. That brings him to Lem. Lem is Emacs reimagined and implemented in Common Lisp.
The developers have made a conscious effort to make Lem familiar to Emacs users but also to make it more general and easier to extend. Take a look at the video or read to transcript for the details.
One thing I like about it is that it’s 100% Common Lisp. There’s no C core; just Lisp all the way down. That makes it easier to customize or extend any part of the editor.
It’s an interesting project but I doubt it will gain much traction among Emacsians. Using Common Lisp solves at lot of problems with Emacs but Emacs users are famously conservative about such things. Just consider the fury that a small change to how registers work provoked (see this reddit post and the Emacs-devel thread about it starting here).
In any event, it’s an interesting talk and worth watching. The video is 18 minutes 27 seconds so plan accordingly.