I recently had a chat with Eben Moglen and rms that suggested that requiring such modules to state in some code-enforced way "I am GPLed" could legally be enough (unlike Eben, I am not a lawyer, and my understanding of what Eben told me could be incorrect). Linux does something like this, by requiring a LICENSE_MODULE macro to be defined for some interfaces. Linux will refuse to load that module if the license isn't GPL, or declares that this Linux is "tainted", and the devs will refuse to support it. I forget. Anyways, Emacs could do this for all of its interfaces and be even stricter than Linux: look for an explicit declaration of GPLness or refuse to load the module. If a module makes the declaration but is lying, they're in legal hot water.

Eben is just about the only legal advice that rms will really listen to. If something like this could be done and Eben convinces rms about this, this may ease his (in my opinion) well-founded fears against proprietary Emacs extensions.

> I think it would be a tremendous waste of effort to rewrite Emacs libraries in any language other than Emacs Lisp. Thus, what interests me is the idea of supporting other languages in addition to Emacs Lisp.

https://lists.gnu.org/archive/html/emacs-devel/2010-04/msg00...

> Common Lisp is extremely complicated and ugly. When I wrote GNU Emacs I had just finished implementing Common Lisp, and I did not like it much. It would bloat Emacs terribly, and documenting it would be hard too.

> Scheme is elegant, and it is a better direction to move in.

> Since we have our own Scheme implementation, we should use that one. If it has a serious disadvantage, we should do something about that. There are various things that might be right to do, but simply disregarding it in the case of Emacs cannot be right.

https://lists.gnu.org/archive/html/emacs-devel/2010-04/msg00...