type DeltaLog     = Writer [String]
type DeltaWithLog = DeltaM DeltaLog

returnW :: (Show a) => a -> DeltaLog a
returnW x = do tell ([show x])
               return x

deltaAppend :: Delta a -> Delta a -> Delta a
deltaAppend (Mono x) d     = Delta x d
deltaAppend (Delta x d) ds = Delta x (deltaAppend d ds)

deltaFromList :: [a] -> Delta a
deltaFromList = (foldl1 deltaAppend) . (fmap return)



generatorM :: Int -> DeltaWithLog [Int]
generatorM x = let intList = [1..x] in
    DeltaM (deltaFromList (fmap returnW (replicate 2 intList)))

numberFilterM :: [Int] -> DeltaWithLog [Int]
numberFilterM xs = let primeList = filter isPrime xs
                       evenList  = filter even xs    in
    DeltaM (deltaFromList (fmap returnW [primeList, evenList]))


countM :: [Int] -> DeltaWithLog Int
countM xs = let numberCount = length xs in
    DeltaM (deltaFromList (fmap returnW (replicate 2 numberCount)))

numberCountM :: Int -> DeltaWithLog Int
numberCountM x = generatorM x >>= numberFilterM >>= countM