new files

Task/Knuth-shuffle/Haskell/knuth-shuffle-1.hs

@@ -0,0 +1,17 @@
+import System.Random
+import Data.List
+import Control.Monad
+import Control.Arrow
+
+mkRands = mapM (randomRIO.(,)0 ). enumFromTo 1. pred
+
+replaceAt :: Int -> a -> [a] -> [a]
+replaceAt i c = let (a,b) = splitAt i l in a++x:(drop 1 b)
+
+swapElems :: (Int, Int) -> [a] -> [a]
+swapElems (i,j) xs | i==j = xs
+                   | otherwise = replaceAt j (xs!!i) $ replaceAt i (xs!!j) xs
+
+knuthShuffle :: [a] -> IO [a]
+knuthShuffle xs =
+  liftM (foldr swapElems xs. zip [1..]) (mkRands (length xs))

Task/Knuth-shuffle/Haskell/knuth-shuffle-2.hs

@@ -0,0 +1,3 @@
+knuthShuffleProcess :: (Show a) => [a] -> IO ()
+knuthShuffleProcess =
+   (mapM_ print. reverse =<<). ap (fmap. (. zip [1..]). scanr swapElems) (mkRands. length)

Task/Knuth-shuffle/Haskell/knuth-shuffle-3.hs

@@ -0,0 +1,21 @@
+import Data.Array.ST
+import Data.STRef
+import Control.Monad
+import Control.Monad.ST
+import Control.Arrow
+import System.Random
+
+shuffle :: RandomGen g => [a] -> g -> ([a], g)
+shuffle list g = runST $ do
+    r <- newSTRef g
+    let rand range = liftM (randomR range) (readSTRef r) >>=
+            runKleisli (second (Kleisli $ writeSTRef r) >>> arr fst)
+    a <- newAry (1, len) list
+    forM_ [len, len - 1 .. 2] $ \n -> do
+        k <- rand (1, n)
+        liftM2 (,) (readArray a k) (readArray a n) >>=
+           runKleisli (Kleisli (writeArray a n) *** Kleisli (writeArray a k))
+    liftM2 (,) (getElems a) (readSTRef r)
+  where len = length list
+        newAry :: (Int, Int) -> [a] -> ST s (STArray s Int a)
+        newAry = newListArray