bogosort haskell

Haskell/bogosort.hs

@@ -0,0 +1,30 @@
+import System.Random
+import Data.Array.IO
+import Control.Monad
+
+isSortedBy :: (a -> a -> Bool) -> [a] -> Bool
+isSortedBy _ [] = True
+isSortedBy f xs = all (uncurry f) . (zip <*> tail) $ xs
+
+
+-- 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
+
+bogosortBy :: (a -> a -> Bool) -> [a] -> IO [a]
+bogosortBy f xs | isSortedBy f xs = return xs
+                | otherwise       = shuffle xs >>= bogosortBy f
+
+bogosort :: Ord a => [a] -> IO [a]
+bogosort = bogosortBy (<)