At 11:24 PM 7/8/2007, zou lunkai wrote:
For swf>=5, The observed results here are:
trace(NaN == NaN); //true
trace(NaN >= NaN); //true
trace(NaN <= NaN); //true
trace(NaN > NaN); //undefined
trace(NaN < NaN); //undefined
trace(NaN != NaN); //false
I'm just whinging here, but all these should return "undefined" in the
mathematically-correct world. If the comparisons are on numbers, and you
have a meta-value that means not-a-number, but the comparisons between
numbers, as functions on the set "numbers union special-value" would be
partial functions defined only on pairs of numbers and be undefined if one
or both elements of the pair were not a number.
This is less purely academic that it sounds. Not-a-number means "I have no
information". It does not mean "I have a special new kind of number with
special axiomatic properties". To say that "a=b" when both are not a
number means asserting that "I have no information about a, and I have no
information about b, but I know they're the same." Put this in some
generic algorithm with wonky input data, and you'll get an unintended
(therefore incorrect) result.
This is all FYI. I am promoting no cause to fix AS.
Incidentally, this argument isn't the same for underflow and overflow
meta-values. Overflow creates a compact representation of infinity, and
underflow creates a non-Haussdorf point at 0, i.e. three topologically
inseparable values, but these are still well-defined spaces.
Eric
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