Comparison of exceptional IEEE floating point numbers, like Nan, seems
to have some bugs in ghci (version 6.12.1).
These are correct, according to the IEEE floating point standards:
Prelude> 0 < (0/0)
False
Prelude> 0 > (0/0)
False
Prelude> 0 == (0/0)
False
But these are inconsistent with the above, and arguably incorrect:
Prelude> compare (0/0) (0/0)
GT
Prelude> compare (0/0) 0
GT
Prelude> compare 0 (0/0)
GT
Prelude> compare (0/0) (1/0)
GT
Prelude> compare (1/0) (0/0)
GT
I'd suggest that compare involving a NaN should yield
error "violation of the law of the excluded middle"
The min and max functions have strange behaviour with regard to NaN,
especially when mixed with Infinity:
Prelude> max (0/0) (1/0)
NaN
Prelude> max (1/0) (0/0)
Infinity
Prelude> min (0/0) (1/0)
Infinity
Prelude> max (0/0) 0
NaN
Prelude> max 0 (0/0)
0.0
Hugs (Version: September 2006) has similar issues:
Hugs> compare (0/0) (0/0)
EQ
Hugs> compare (0/0) 1
EQ
Hugs> (0/0) == (0/0)
False
Hugs> min (0/0) 1
nan
Hugs> min 1 (0/0)
1.0
Hugs> max (0/0) 1
1.0
Discuss?
--
Barak A. Pearlmutter