úΟ8     (c) 2011 Brent YorgeyBSD-style (see LICENSE)byorgey@cis.upenn.eduNone246B \Class of monads which support a state along with a stack for saving and restoring states.OA monad transformer which adds a save/restorable state to an existing monad.Run a  StateStackT‹ computation from an initial state, resulting in a computation of the underlying monad which yields the return value and final state.Like , but discard the final state. Like A, but discard the return value and yield only the final state. Run a  StateStacke computation from an initial state, resulting in a pair of the final return value and final state. Like  , but discard the final state. Like  A, but discard the return value and yield only the final state. StateT& computations can always be lifted to  StateStackT9 computations which do not manipulate the state stack.#Save the current state on the stack$Restore the top state from the stack         statestack-0.2.0.4Control.Monad.StateStack StateStackMonadStateStacksaverestore StateStackT unStateStackTrunStateStackTevalStateStackTexecStateStackT runStateStackevalStateStackexecStateStack liftState$fMonadContStateStackT$fMonadStateStacksWriterT$fMonadStateStacksWriterT0$fMonadStateStacksStateT$fMonadStateStacksStateT0$fMonadStateStacksReaderT$fMonadStateStacksMaybeT$fMonadStateStacksListT$fMonadStateStacksIdentityT$fMonadStateStacksExceptT$fMonadStateStacksContT$fMonadStateStacksStateStackT$fMonadStatesStateStackT