-- MonadicRandomGenerator.hs (Learn You a Haskell for Great G |	-- DesugaredMonadicRandomGenerator.hs (Learn You a Haskell fo

import System.Random  						import System.Random  
import Control.Monad.State  					import Control.Monad.State  

randomSt :: (RandomGen g, Random a) => State g a  		randomSt :: (RandomGen g, Random a) => State g a  
-- The following line was wrong in the book:		      |	randomSt =
-- randomSt = State random				      |	 get >>=
randomSt = do						      |	 \gen -> 
 gen <- get						      |	  let (value,nextGen) = random gen
 let (value,nextGen) = random gen			      |	  in
 put nextGen						      |	   put nextGen >>
 return value						      |	   return value

randomSt1 = (runState randomSt (mkStdGen 1)) :: (Int,StdGen)	randomSt1 = (runState randomSt (mkStdGen 1)) :: (Int,StdGen)
randomSt2 = (runState randomSt (mkStdGen 2)) :: (Float,StdGen	randomSt2 = (runState randomSt (mkStdGen 2)) :: (Float,StdGen

threeCoins :: State StdGen (Bool,Bool,Bool)  		      |	threeCoins :: State StdGen (Bool,Bool,Bool)
threeCoins = do  					      |	threeCoins =
 a <- randomSt  					      |	 randomSt >>=
 b <- randomSt  					      |	 \a -> randomSt >>=
 c <- randomSt  					      |	 \b -> randomSt >>=
 return (a,b,c)  					      |	 \c -> return (a,b,c)

threeCoins1 = runState threeCoins (mkStdGen 33)			threeCoins1 = runState threeCoins (mkStdGen 33)
threeCoins2 = runState threeCoins (mkStdGen 2)			threeCoins2 = runState threeCoins (mkStdGen 2)

-- rollDie and rollNDice are not explained in the book LYAHFG	-- rollDie and rollNDice are not explained in the book LYAHFG
-- But these functions are interesting and complementary:	-- But these functions are interesting and complementary:

rollDie :: State StdGen Int					rollDie :: State StdGen Int
rollDie = do 						      |	rollDie =
 generator <- get					      |	 get >>=
 let (value, newGenerator) = randomR (1,6) generator	      |	 \generator -> 
 put newGenerator					      |	  let (value, newGenerator) = randomR (1,6) generator
 return value						      |	  in
							      >	   put newGenerator >>
							      >	   return value

rollDie1 = runState rollDie (mkStdGen 1)			rollDie1 = runState rollDie (mkStdGen 1)
rollDie2 = runState rollDie (mkStdGen 2)			rollDie2 = runState rollDie (mkStdGen 2)

rollNDice :: Int -> State StdGen [Int]				rollNDice :: Int -> State StdGen [Int]
rollNDice 0 = do					      |	rollNDice 0 = return []
 return []						      |	rollNDice n =
rollNDice n = do					      |	 rollDie >>=
 value <- rollDie					      |	 \value -> rollNDice (n-1) >>=
 list <- rollNDice (n-1)				      |	 \list -> return (value:list)
 return (value:list)					      <

rollNDice1 = runState (rollNDice 10) (mkStdGen 1)		rollNDice1 = runState (rollNDice 10) (mkStdGen 1)
rollNDice2 = runState (rollNDice 20) (mkStdGen 2)	      |	rollNDice2 = runState (rollNDice 20) (mkStdGen 2)