Date: Mon, 24 Oct 2005 04:27:08 +0200
   From: Marcin 'Qrczak' Kowalczyk <xxxxxx@knm.org.pl>

   Taylor Campbell <xxxxxx@mumble.net> writes:

   > this is typically what is done with exact arithmetic, such as in
   > Scheme48:
   >
   > (/ 0 0)     => Error: rational division by zero

   Of course; because in the case of exact arithmetic the problem
   definitely means that the function is undefined at this point.
   With inexact arithmetic it might just result from rounding errors,
   so a computation can't expect it in advance, thus it's not generally
   a symptom of a bug.

Conditions do not imply bugs.  They are just that: conditions.  How
they are detected is a matter unrelated to their fundamental purpose.
NaN is a condition, just like the end of an input stream; it's not an
actual numerical value, though it is produced as a result of IEEE 754
numerical operations, just as an EOF object is not any element of an
input stream but is produced by procedures that read from them; and
neither necessarily implies a bug in a program.