fooling around with the state monad

fooling_around.hs

import System.Random
import Control.Monad.State

-- given a [Int] add random numbers to it
a :: [Int]
a = [3, 1, 6, 7, 9]

myFunc :: Int -> State StdGen Int
myFunc x = do
             gen <- get
             let (y, gen2) = randomR (100,200) gen
             put gen2
             return $ y + x

myFunc2 :: Int -> State StdGen (Maybe Int)
myFunc2 0 = return Nothing
myFunc2 x = do
              gen <- get
              let (y, gen2) = randomR (100,200) gen
              put gen2
              return $ Just $ y*x

myFunc3 :: Int -> State StdGen (Maybe Int)
myFunc3 1000 = return Nothing
myFunc3 x = do
              gen <- get
              let (y, gen2) = randomR (100,200) gen
              put gen2
              return $ Just $ y*x + 2

myConnector :: Maybe Int ->  State StdGen (Maybe Int)
myConnector (Just 1000) = return Nothing
myConnector (Just x) = myFunc3 x

x :: State StdGen [Int]
x = mapM myFunc a

y :: [Int] -> State StdGen [Maybe Int]
y = mapM myFunc2  

z :: [Maybe Int] -> State StdGen ([Maybe Int])
z = mapM myConnector 

g = evalState (x >>= (z <=< y ))  (mkStdGen 4567)