Am Freitag, 11. Januar 2008 11:03 schrieb Felipe Lessa:
Another thing for the record: Goldberg says
"The introduction of NaNs can be confusing, because a NaN is never equal to any other number (including another NaN), so x = x is no longer always true. In fact, the expression x /= x is the simplest way to test for a NaN if the IEEE recommended function Isnan is not provided. Furthermore, NaNs are unordered with respect to all other numbers, so x <= y cannot be defined as not x > y. Since the introduction of NaNs causes floating-point numbers to become partially ordered, a compare function that returns one of <, =, >, or unordered can make it easier for the programmer to deal with comparisons."
Goldberg, David. What Every Computer Scientist Should Know About Floating-Point Arithmetic. http://docs.sun.com/source/806-3568/ncg_goldberg.html .
As GNU is not Unix, NaN is not a number, so what is standard about numbers doesn't work for them. I don't think there's a compeling reason about changing this behavior, specially because it's what's specified in the IEEE 754.
There is a really compelling reason: If the order on floating point numbers is partial then there is no meaningful Ord instance for them. And what do Hugs and GHCi say? Their answers are plain horror: Hugs, version 20050308: compare (0 / 0) (0 / 0) => EQ 0 / 0 == 0 / 0 => False GHCi 6.8.2: compare (0 / 0) (0 / 0) => GT 0 / 0 > 0 / 0 => False Anyone interested in filing bug reports?
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Best wishes, Wolfgang