Re: GC: marking traversal and pure symbols

[Ken Raeburn <raeburn@raeburn.org>]

On Jul 6, 2007, at 00:38, Richard Stallman wrote:
> We can't make Qnil pure, because its plist can be written.
> (It can also be defined as a function, though that would be an
> ugly thing to do.)

I've seen that done, many years ago -- and the person who did it ran  
into interesting problems.  I think there was some Emacs code shipped  
that had a loop over a list testing to see if the car of the list was  
a function, or something like that -- depending on the fact that nil  
doesn't (normally) have a function binding to break the loop.  I have  
no idea if the problem is still present.

It wouldn't strike me as a bad thing to make the function slot of  
Qnil unsettable this way...

Ken