ekmett/lens — pull request #481 by sordina (2014-09-23 12:42:56+00:00)
Title: Added xorish operators to Data.Bits.Lens

Inspired by http://en.wikipedia.org/wiki/Rijndael_S-box#Implementations

```haskell
affineX :: Word8 -> Word8 -> Word8
affineX c b = b &~ forM_ [0..7] twiddle
where
twiddle j = do bitAt j .= getBit b 4
bitAt j .^.= getBit b 5
bitAt j .^.= getBit b 6
bitAt j .^.= getBit b 7
bitAt j .^.= getBit c 0
where
getBit n o = n ^. bitAt (mod (o + j) 8)
```