Date: Mon, 24 Oct 2005 03:45:41 +0200
   From: Marcin 'Qrczak' Kowalczyk <xxxxxx@knm.org.pl>

   Could you show an object which does not have read syntax in Lisp
   *because* it's an error object?

   Common Lisp condition objects, if you mean them. are not comparable to
   NaN. A condition is caught out of band; a NaN is returned instead of
   a more exact result and gets printed along with the normal way of
   printing results.

CL conditions *are* comparable to NaN.  Nothing states that CL
conditions can exist *only* if they are immediately passed to a
condition handler, and NaN could just as well be a CL-style condition
(or a Scheme equivalent thereof, like MIT Scheme's condition system);
NaN could also just as well be signalled by the operation instead of
being returned by it.

EOF objects are another example of condition objects (in the general
sense, which has been erroneously referred to as 'error object') with
no printed representation.

   When one part of the program prints numeric results to a file, and
   another part later reads them, what is the point in breaking this
   communication channel for NaNs?

NaN is *not* a numeric result; it's not a number!  It represents the
condition of a computation whose meaning is undefined; it's not a
defined result.