15 Apr
2010
15 Apr
'10
3:22 p.m.
On 2010-04-15 06:18, Nick Bowler wrote:
Your definitions seem very strange, because according to this, the functions
f :: Double -> Double f x = 1/x
and
g :: Double -> Double g x = 1/x
are not equal, since (-0.0 == 0.0) yet f (-0.0) /= g (0.0).
There's an impedance mismatch between the IEEE notion of equality (under which -0.0 == 0.0), and the Haskell notion of equality (where we'd want x == y to imply f x == f y). A Haskellish solution would be to implement Eq so that it compares the bits of the representations of Float and Double, thus -0.0 /= 0.0, NaN == NaN (if it's the same NaN). But this might surprise people expecting IEEE equality, which is probably almost everyone using Float or Double. -- Ashley Yakeley