haskell - 如何洗牌？

Question

如何在不替换的情况下从一组数字( [1, 2, 3] )中采样，直到我点击 x ?
我的计划是洗牌[1, 2, 3]并在 x 处截取:

-- chopAt 3 [2, 3, 1] == [2, 3]
-- chopAt 3 [2, 1, 3] == [2, 1, 3]
-- chopAt 3 [3, 1, 2] == [3]
chopAt _ [] = []
chopAt x (y:ys)
  | x /= y    = y : chopAt x ys
  | otherwise = [y]

但是我不知道如何洗牌(或理解 Monads)。

-- sample without replacement from [1, 2, 3] until one hits a 3
-- x <- shuffle [1, 2, 3]
-- print (chopAt 3 x)
main = do
-- shuffle [1, 2, 3]
  print (chopAt 3 [1, 3, 2])

Answer 1

要对列表进行洗牌，请使用 random-shuffle图书馆:

import System.Random (newStdGen)
import System.Random.Shuffle (shuffle')

main = do
  rng <- newStdGen

  let xs = [1,2,3,4,5]

  print $ shuffle' xs (length xs) rng