Numbers and Pork Rinds

[Guy Steele <gls@think.com>]

   Date: Sun, 27 Aug 89 14:30 PDT
   From: Alan Bawden <bawden@arisia.xerox.com>

   Floating point numbers can be used as a representation for exact (rational)
   numbers as well, if an implementation chooses.  But since the set of
   rationals represented exactly by floating point is not even approximately
   closed under even the most common operations (consider (/ 1 3) or 
   (+ 1 1000000000000000000000000000000)), this doesn't seem to be a viable
   choice.

Actually, an implementation using IEEE arithmetic might find it completely
convenient to have both exact and inexact floats; a result float would be
exact if all inputs are exact AND the IEEE operation(s) reported no inexact
exception.  (This is a minor point.)
--Guy