On Mar 25, 2010, at 4:22 AM, Nick Coghlan wrote: > Mark Dickinson wrote: >> Here's an interesting recent blog post on this subject, from the >> creator of Eiffel: >> >> http://bertrandmeyer.com/2010/02/06/reflexivity-and-other-pillars-of-civilization/ > > Interesting. So the natural tweak that would arise from that perspective > is for us to restore reflexivity by declaring that any given NaN is > equal to *itself* but not to any other NaN (even one with the same payload). > > With NaN (in general) not being interned, that would actually fit the > idea of a NaN implicitly carrying the operation that created the NaN as > part of its definition of equivalence. > > So, I'm specifically putting that proposal on the table for both float > and Decimal NaNs in Python: > > "Not a Number" is not a single floating point value. Instead each > instance is a distinct value representing the precise conditions that > created it. Thus, two "NaN" values x and y will compare equal iff they > are the exact same NaN object (i.e. "if isnan(x) then x == y iff > x is y". > > As stated above, such a change would allow us to restore reflexivity > (eliminating a bunch of weirdness) while still honouring the idea of NaN > being a set of values rather than a single value. > +1 Raymond
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