Implementation of shuffle for smallcheck

gistfile1.hs

import Test.SmallCheck
import Test.SmallCheck.Series
import Data.Bifunctor
import Control.Monad

-- Based on the implementation in quickcheck: http://hackage.haskell.org/package/QuickCheck-2.8.1/docs/src/Test-QuickCheck-Gen.html#shuffle
shuffle [] = return []
shuffle xs = do
  (y, ys) <- uncurry mplus $ bimap msum msum $ bimap (map return) (map $ decDepth . return) $ splitAt 1 $ selectOne xs
  (y:) <$> decDepthChecked (return ys) (shuffle ys)
  where selectOne [] = []
        selectOne (y:ys) = (y,ys) : map (second (y:)) (selectOne ys)