I wrote a few variants for fun. Probably equally inefficient. I suggest you look at Data.Binary as Andrew suggested. -- Your original function, but with a more generic type signature. encodeBits :: Bits n => [Bool] -> n encodeBits bs = go 0 0 bs where go n r [] = r go n r (b:bs) = go (n+1) (if b then setBit r n else clearBit r n) bs -- Combine the flags with their index and then set bits when appropriate. encodeBits2 :: Bits n => [Bool] -> n encodeBits2 = foldr (\(n, b) x -> setBitIf b x n) 0 . zip [0..] where setBitIf False x _ = x setBitIf True x n = setBit x n -- Shift the result left while constructing and only toggle the first bit. encodeBits3 :: Bits n => [Bool] -> n encodeBits3 bs = foldr (\b x -> setBitIf b (x `shiftL` 1)) 0 bs where setBitIf False x = x setBitIf True x = setBit x 0

Thanks for the answers. I already had a look at Binary but, as said above, it doesn't support bit manipulation, only bytes. On Wed, Sep 30, 2009 at 11:18:03AM +0200, Paul.Brauner@loria.fr wrote:

Hello,

I haven't found a function in hackage or in the standard library that takes a list of booleans (or a list of 0s and 1s, or a tuple of booleans or 0s and 1s) and outputs a Word8 or Word32.

I have written one which seems very inefficient :

toWord8 :: [Bool] -> Word8 toWord8 bs = go 0 0 bs where go n r [] = r go n r (b:bs) = go (n+1) (if b then setBit r n else clearBit r n) bs

Is there a better way to do this out there ?

(If it helps, i'm writting a toy compression algorithm, which outputs binary as lists of booleans, and I'd like to output that in a file).

Cheers Paul _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe