Steve Haflich wrote:
> See *print-circle* in your favorite copy of the ANSI CL specification,
> or in CLtL2.
Thanks. This allowed me to find the more explicit (for me) explanation in
http://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node191.html
#n=
The syntax #n=object reads as whatever Lisp object has object as its
printed representation. However, that object is labelled by n, a required
unsigned decimal integer, for possible reference by the syntax #n# (below).
The scope of the label is the expression being read by the outermost call to
read. Within this expression the same label may not appear twice.
#n#
The syntax #n#, where n is a required unsigned decimal integer, serves
as a reference to some object labelled by #n=; that is, #n# represents a
pointer to the same identical (eq) object labelled by #n=. This permits
notation of structures with shared or circular substructure.
--
Michel Talon