Re: Bits Problem

6 Apr 2003

      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

-- 
Glynn Clements <glynn.clements@virgin.net>