module NumberPrint where

import Control.Monad         (when)
import Data.IORef            (newIORef)
import Data.StateVar         (($=), ($~), get)
import Foreign.Ptr           (Ptr (..))
import Foreign.Marshal.Alloc (alloca)
import System.IO.Unsafe      (unsafePerformIO)

whileM :: Monad m => m Bool -> m () -> m ()
whileM mb a = do
  b <- mb
  when b $ a >> whileM mb a

numberprint :: Int -> Integer
numberprint n = read . unsafePerformIO $ do 
  alloca $ \(i :: Ptr Int)-> do
    i $= 1
    s <- newIORef ""
    whileM ((<n) <$> get i) $ do
      c <- get i
      s $~ (show c++)
      i $~ (1+)
    whileM ((>= 1) <$> get i) $ do
      c <- get i
      s $~ (show c++)
      i $~ (-1+)
    get s
 

module AddNumbers where
import Data.Monoid( Sum(..) )

add_arr :: [Int] -> Int
add_arr = getSum . foldMap Sum