I’m pretty new to Haskell although I did some ML many moons ago.

I’m trying to set up a deck of playing cards, shuffle them and then deal them. I have the deck and shuffle sorted (of a fashion) but I’m not sure what I’m doing after that.

This is what I have so far:

import System.Random
import Data.Array.IO
import Control.Monad

-- | Randomly shuffle a list
--   /O(N)/
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

ranks=[2..14]

suits=[1,2,3,4]

cards=[(r,s) | r <- ranks, s<- suits]

deck=shuffle cards


myAction :: IO [(Integer, Integer)]
myAction = shuffle cards

main :: IO ()
main = do
    xs <- myAction
    print xs

There was no particular reason I chose that list shuffler other than the reason I could interrogate (or at least display) the resulting list.

I’d like to be able to pull items off the returned IO [(Integer, Integer)] but I’m not entirely sure how to proceed. I understand that I can’t simply convert it to a vanilla list (this is covered sufficiently elsewhere) so presumably I either need to:

• extend the IO (monad?) somehow
• write a custom list of tuples shuffler
• write my own monad
• use some other method I haven’t learnt yet

Anecdotally, I believe this can be done “uncleanly” but I don’t want to go to programmer hell until I understand how hot the fires are…

Any idea how best to proceed?