úÎÆ     byorgey@cis.upenn.edu=Class of monads which support a state along with a stack for  saving and restoring states. $Save the current state on the stack %Restore the top state from the stack %A monad transformer which adds a save/restorable state to an  existing monad. Run a  StateStackT. computation from an initial state, resulting D in a computation of the underlying monad which yields the return  value and final state. Like , but discard the final state. Like ), but discard the return value and yield  only the final state. Run a  StateStack. computation from an initial state, resulting 8 in a pair of the final return value and final state. Like  , but discard the final state. Like  ), but discard the return value and yield  only the final state. StateT& computations can always be lifted to  StateStackT 9 computations which do not manipulate the state stack.         statestack-0.1Control.Monad.StateStack StateStackMonadStateStacksaverestore StateStackT unStateStackTrunStateStackTevalStateStackTexecStateStackT runStateStackevalStateStackexecStateStack liftState