Date: Sat, 29 Oct 2005 22:58:12 -0700
   From: Alan Watson <xxxxxx@astrosmo.unam.mx>

   Perhaps we need to defined a general invalid object which has (a) no
   read syntax and (b) is returned by read whenever it has a problem with
   the input (numbers too big, objects to big, bad syntax, etc.)

Why not *signal* a condition?