Guile Scheme Emacs-Lisp Compatibility Matures
In a posting to the Guile developers list
today, it was announced that the Emacs-Lisp
compiler for Guile has matured enough to run actual elisp
programs. The author included a screencast demoing
the new compiler running the Dunnet
dungeon crawler. It is still a bit hackish: you need a load file that fakes a few Emacs side functions. In theory, most batch mode programs that don't do buffer manipulation should now work. After a few previous attempts, things could be on track for GNU Emacs 25 based on Guile.
TeXmacs and Lilypond also embed Guile.
There are many other apps using it, like gnucash.
Having used it before I can tell you that the C API is very well made, and C and scheme can call each other with few limitations. Scheme is an elegant language too.
Lua has three main advantages over guile. It is trivial to package, has a smaller footprint, and works anywhere. Guile only really supports posix and windows.
But the main competitor to guile is not lua, it is python. And the battle is all but lost. The two offer about the same functionality. They can easily interface with the outside (unlike Lua) and the C API works similarly, but python wins due to its more traditional syntax and larger developer base.
As much as I like guile, the whole point of an extension language is to encourage third-party additions, so you want a language that attracts as many potential developers as possible (including beginners), and that language is not scheme. So unless your religion forbids it (i.e. it is a gnu program), python, or maybe javascript, is almost always a better choice.
Lilypond uses Guile extensively, and as time goes on, more and more of its code has been moving from C++ to Guile. For those not in the know, Lilypond is a typesetting program for music.
This is the kind of article I'm always glad to see on Slashdot; emacs is cool, Lisp is cool, an article on something that's genuinely hardcore nerdy is always good to see! With the Linux on 8-bit micro article also posted today it feels like the nerd coefficient is running high today! Good!
But don't let that discourage you too much, lisp might be worth learning in any case.