Thanks.
Fusing the ws is trickier. Directly appealing to the fibonacci-number example is not recommended because this would mean to keep the last 16 ws in memory and shifting them right to left by hand. But as the
Are you saying this because we don't want a 16-tuple?
"Alternate method of computation" on the website suggests, you can delegate the shifting to an index that shifts around mod 16. Having a mutable array is helpful, then.
Are you saying that because haskell doesn't really have mutable arrays, this is ruled out?
Of course, you can also fill a large static (boxed!) array of 80 Word8s via
ws :: Data.Array.IArray.Array Int Word8 ws = accumArray 0 (0,80) (curry snd) $ zip [0..15] xs ++ [(i, xxor i) | i<-[16..80]] where xxor i = ws ! (i-16) `xor` ws ! (i-3) `xor` ws ! (i-8) `xor` ws ! (i-14)
or something like that (I didn't care about correct indices and bounds). GHC can fuse such array accumulations.
Why is an array better than a list? Is it because (!) is O(1) and (!!) is O(n)?
In general, keeping stuff in lists is not wrong, but ByteStrings are more adapted to current CPU and RAM architecture.
I'm not clear how ByteStrings help here. We need to put bits into 32 words and operate on these. Dominic.