Proposal: Remove Num superclass of Bits

[basvandijk]

This ticket summarizes the  discussion on the proposal to remove the Num superclass of the Bits type class.

The proposal is to:

• Remove the Num superclass of the Bits type class.

• Remove the default implementations of bit, testBit and popCount since they use methods of Num.

• Export the following convenience functions from Data.Bits:

bitDefault :: (Bits a, Num a) => Int -> a
bitDefault i = 1 `shiftL` i

testBitDefault ::  (Bits a, Num a) => a -> Int -> Bool
testBitDefault x i = (x .&. bit i) /= 0

popCountDefault :: (Bits a, Num a) => a -> Int
popCountDefault = go 0
 where
   go !c 0 = c
   go c w = go (c+1) (w .&. w - 1) -- clear the least significant

Attached are tickets for base and ghc.

[basvandijk]

Patch for base

[basvandijk]

Patch for ghc

[igloo]

Thanks, applied:

commit f99cee0118c6bbcd0283ea795a3bb6ff6090b5b5
Author: Bas van Dijk <v.dijk.bas@gmail.com>
Date:   Sat Oct 29 03:33:08 2011 +0200

    Remove Num superclass of Bits Add and export bitDefault, testBitDefault and
popCountDefault from Data.Bits.

commit 804108f0c0fbc2c5f926e4cb4d30b3891443a079

Author: Bas van Dijk <v.dijk.bas@gmail.com>
Date:   Sat Oct 29 03:38:07 2011 +0200

    Add extra Num constraints since the Num superclass of Bits is removed