On Numbers

[Mike Meyer]

In the discussion of equality, the issue that decimal('3.0') == 3.0 is
False came up as a reason for changing the behavior of ==. The problem
with this is that the proposed change doesn't really fix anything, it
just gives different wrong behavior. The correct fix would seem to be
fixing python's handling of numbers.

It's not clear from the PEP why test for equality always fails. While
the PEP says that interactions with floats are disallowed as "to
tricky", comparisons seem to be an exception. In particular, equality
comparisons seem to always return false, whereas checking for
magnitude seems to work.

What appears to be missing in Python is a coherent model for all
numberic types. Other languages have this, so there's no obvious
reason that Python can't. Or maybe Python does, and I've overlooked
it. In that case, pointers to documentation would be appreciated.
If it doesn't exist, then I think this is something that should be
addressed for Py3K.

I'd like to work on that. The idea would be that all the numeric types
are representations of reals with different properties that make them
appropriate for different uses. The goal would be a model for a
numeric type that captures those properties in a way that allows them
to be combined to give sane behavior without being "to tricky".

To get started on that, I want to consider how other languages with
rich numeric type systems model them. I'm going to look at a couple of
languages in the LISP family. I'd like to solicit the community for
the names of languages (and pointers to references, if possible!) with
a coherent view of a rich set of numeric types.

      Thanks,
      <mike
-- 
Mike Meyer <mwm at mired.org>			http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.