fork(3) download

import System.Random
 
shuffle :: Int -> [Int] -> IO [Int]
shuffle 0 xs = return xs
shuffle i xs = do
	n <- getStdRandom $ randomR (0, (length xs) - 1) :: IO Int
	let part1 = take n xs
	    part2 = drop (n + 1) xs
	    flipped = [xs !! n] ++ part1 ++ part2
	return (shuffle (i - 1) flipped)
 
main = do
	shuffle 10 [1..9] >>= print

[1 of 1] Compiling Main             ( prog.hs, prog.o )

prog.hs:10:9: error:
    • Couldn't match type ‘IO [Int]’ with ‘[Int]’
      Expected type: IO [Int]
        Actual type: IO (IO [Int])
    • In a stmt of a 'do' block: return (shuffle (i - 1) flipped)
      In the expression:
        do { n <- getStdRandom $ randomR (0, (length xs) - 1) :: IO Int;
             let part1 = take n xs
                 part2 = drop (n + 1) xs
                 ....;
             return (shuffle (i - 1) flipped) }
      In an equation for ‘shuffle’:
          shuffle i xs
            = do { n <- getStdRandom $ randomR (0, (length xs) - 1) :: IO Int;
                   let part1 = ...
                       ....;
                   return (shuffle (i - 1) flipped) }

Standard output is empty