[Haskell-cafe] GHC optimisations

[Stefan O'Rear]

On Wed, Aug 22, 2007 at 06:36:15PM +0100, Neil Mitchell wrote:
> Hi
> 
> > If Num obeys ring axioms, fromInteger is a perfectly fine
> > ring-homomorphism. (It's also the first or second homomorphism taught.)
> 
> Does Int obey these axioms? I'm thinking that assuming properties
> about things such as numbers is very likely to go wrong very quickly.
> Monads you might be able to get away with, Numbers you probably can't.

Int does obey the axioms, it's the classical ring ℤ[4294967296].
Double, however, does not:

stefan at stefans:~$ ghci
GHCi, version 6.7.20070712: http://www.haskell.org/ghc/  :? for help
Loading package base ... linking ... done.
Prelude> let x = 10000000000000000000000 ; y = 1 - x
Prelude> fromInteger (x + y) :: Double
1.0
Prelude> fromInteger x + fromInteger y :: Double
0.0


Stefan
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