bignums are bogus

[Masinter.pa@Xerox.COM]

The only practical way I know of dealing with storage limits and the
like in a programmatic way is to treat reaching them as well defined
exceptional situations which signal conditions. Programs that care, such
as those in embedded systems, can catch those exceptional situations and
do something reasonable with them, whether it is a bignum storage
overflow or running out of CONS space. 

This is addressed in part in the exceptional-situations-in-Lisp
proposal, which is still (apparently) in committee.