On Wed, 6 Jul 2005, Aubrey Jaffer wrote:

> | Thereby hypothetically: (presuming sufficient numerical precision)
> |
> | (tan pi/2) => 0
>
>An exact zero?  That is just wrong.

No, actually it's more right than we expect computation to
get.  If pi/2 can be an exact number in the representation
used by the scheme system, an exact zero is precisely the
correct response to (tan pi/2).  That said, tan isn't one
of the functions that is required to return an exact result
given exact arguments, so even if pi/2 is exact in the number
representation, we still aren't *required* to return the
exact zero, even though it's true.

In the usual case, where the numeric representation does
not allow pi/2 to be expressed as an exact number, then we
have an operation on an inexact number and we *must* return
an inexact result.

				Bear