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Task/Sorting-algorithms-Bogosort/Haskell/sorting-algorithms-bogosort.hs

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+import System.Random
+import Data.Array.IO
+import Control.Monad
+
+isSorted :: (Ord a) => [a] -> Bool
+isSorted (e1:e2:r) = e1 <= e2 && isSorted (e2:r)
+isSorted _         = True
+
+-- from http://www.haskell.org/haskellwiki/Random_shuffle
+shuffle :: [a] -> IO [a]
+shuffle xs = do
+        ar <- newArray n xs
+        forM [1..n] $ \i -> do
+            j <- randomRIO (i,n)
+            vi <- readArray ar i
+            vj <- readArray ar j
+            writeArray ar j vi
+            return vj
+  where
+    n = length xs
+    newArray :: Int -> [a] -> IO (IOArray Int a)
+    newArray n xs =  newListArray (1,n) xs
+
+bogosort :: (Ord a) => [a] -> IO [a]
+bogosort li | isSorted li = return li
+            | otherwise   = shuffle li >>= bogosort