Greetings All, I am writing code using a BankersDequeue from Data.Dequeue. I’d like to wrap the push and pop operations in a state monad for the standard reason, to avoid passing the dequeue around between function calls, and regard it as state instead, which it is. Wishing to avoid throwing a runtime error if the queue is empty (for the general case of queues) I have written a reduction of the concept using a crude stack to experiment, which uses State and Maybe. I notice that there are very few examples of using State and Maybe together. My questions are: Is this a faulty design pattern? Should this be done with monad transformers? Are there examples to be found of using State with Maybe as a monad transformer combination? Why is this pattern relatively rare, it seems? Is this program on the right track? Andrew — snip module Main where import Control.Monad.State type Stack = [Int] popIt :: Stack -> (Maybe Int, Stack) popIt [] = (Nothing, []) popIt (x:xs) = (Just x, xs) pop :: State Stack (Maybe Int) pop = state popIt push :: Int -> State Stack (Maybe ()) push a = state $ \xs -> (Just (), a:xs) main = do let a = evalState (do push 3 push 2 push 1 pop pop a <- pop return a ) [] print a — snip