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? > […] Best wishes, Wolfgang _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe