On Jan 11, 2008 7:47 AM, Miguel Mitrofanov
However, the fact that (0 / 0) == (0 / 0) yields False is quite shocking.
Just for the record: the following is from Firebug (JavaScript debugger for Firefox) session:
a = 0/0 NaN a == a false a === a false
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. However you can always define something like newtype NotADouble = N Double ... instance Eq NotADouble where N x == N y = (isNaN x && isNaN y) || (x == y) ... -- Felipe.