Circular structure printing

[Daniel L. Weinreb <dlw at SCRC-TENEX at MIT-MC>]

I have become a bit concerned about the Common Lisp feature that
says that the printer should be able to deal with circular list
structure in the manner specified.  One thing that is particularly
worrisome is that the first occurence of a shared cons cell has
to be prefixed with a marker, which means that you have to do
complete lookahead at the entire Lisp object you are printing before
you can output the first character.  Is this really intentional?
Does anybody have a printer that does this?  May I examine the
code, please?  Are the requirements in runtime and storage
really acceptable?  It's quite possible that there's nothing
to worry about and somebody has a great solution, but I'd like
to see it.  Thanks.