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copied!<p>Here's a version, just to prove you can convert code from Wikipedia almost exactly into Haskell ;)</p> <pre><code>import Control.Monad.ST import Data.Array.ST import Data.Foldable import Control.Monad -- wiki-copied code starts here partition arr left right pivotIndex = do pivotValue <- readArray arr pivotIndex swap arr pivotIndex right storeIndex <- foreachWith [left..right-1] left (\i storeIndex -> do val <- readArray arr i if (val <= pivotValue) then do swap arr i storeIndex return (storeIndex + 1) else do return storeIndex ) swap arr storeIndex right return storeIndex qsort arr left right = when (right > left) $ do let pivotIndex = left + ((right-left) `div` 2) newPivot <- partition arr left right pivotIndex qsort arr left (newPivot - 1) qsort arr (newPivot + 1) right -- wrapper to sort a list as an array sortList xs = runST $ do let lastIndex = length xs - 1 arr <- newListArray (0,lastIndex) xs :: ST s (STUArray s Int Int) qsort arr 0 lastIndex newXs <- getElems arr return newXs -- test example main = print $ sortList [212498,127,5981,2749812,74879,126,4,51,2412] -- helpers swap arr left right = do leftVal <- readArray arr left rightVal <- readArray arr right writeArray arr left rightVal writeArray arr right leftVal -- foreachWith takes a list, and a value that can be modified by the function, and -- it returns the modified value after mapping the function over the list. foreachWith xs v f = foldlM (flip f) v xs </code></pre>

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