[no subject]

[GLS at MIT-AI (Guy L. Steele, Jr.)]

CC: GLS at MIT-AI, GJS at MIT-AI

Just as it is useful for (CAR ()) = (CDR ()) = (), so it would
be very useful for any DEFSTRUCT selector to return () when
applied to ().  I'm writing a piece of code for which that would
be INFINITELY convenient.  On the other hand, I'm not sure I
would want the AR-n primitives as such to change (but maybe so?).
Anyway, (SETF (FOOBAR ()) 43) would still barf, just as
(RPLACA () 43) should.  Anyway, it would seem simple to add
something like CAR-SYM-MODE called AR-SYM-MODE or something,
with only two values (error, and error-except-nil).