After reading Daniel Fischer's message about trying to use EnumSet in his Sudoku.hs and finding that it was slower when processing a large data set, I decided to do some profiling. I rewrote his solver to use EnumSets and profiled it. The culprit turns out to be the following function which is responsible for 22% of the allocating in the run. Is there a more efficient way to write this function? foldBits :: Bits c => (a -> Int -> a) -> a -> c -> a foldbits _ z 0 = z foldBits f z bs = foldBits' f 0 bs z foldBits' :: Bits c => (a -> Int -> a) -> Int -> c -> a -> a foldBits' f i bs z | bs == 0 = z | otherwise = z' `seq` foldBits' f i' bs' z' where z' | 1 == bs .&. 1 = f z i | otherwise = z i' = i + 1 bs' = bs `shiftR` 1 ps. I was impressed with how hairy DF's algorithm is and I am not really enough interested in Sudoku to spend the time needed to grok it. So, I decided to try an experiment to see if I could restructure it without understanding it very deeply. Step 1. comment out all the type signatures. Step 2. find the main place that I wanted to change from [Int] to (Set Int) Step 3. compile; make obvious edits; repeat until 0 errors I had it running in a few minutes. I can't imagine doing that in any other programming environment! Cheers, David -------------------------------- David F. Place mailto:d@vidplace.com