I'm confused. Does it mean that objects basing on bits have to be of Num because of an default implementation that they don't use? A List of Bits should be instance of Bits, too. Instead of default imlementations that use Num functions, there could be an instance of all Integrals. (Integer is instance of Bits too, so there should not be any problem with rotations.) class Bits a where ... instance (Integral a) => Bits a where ... Am Sonntag, 6. April 2003 15:35 schrieb Glynn Clements:
Dominic Steinitz wrote:
Can anyone explain this? Hugs doesn't complain.
Prelude> :set --version The Glorious Glasgow Haskell Compilation System, version 5.04.1
test.hs:5: No instance for (Num Bool) arising from the instance declaration at test.hs:5 In the instance declaration for `Bits Bool'
module Main(main) where
import Bits
instance Bits Bool where complement False = True complement True = False
GHC's definition of Bits requires that instances of Bits are also instances of Num.
This constraint is required for the default implementations of bit and testBit:
bit i = 1 `shift` i x `testBit` i = (x .&. bit i) /= 0