Modulestatestack-0.3.1.1Haskell2010

Control.Monad.StateStack

A state monad which allows the state to be saved and restored on a stack.

Computation type:: Computations with implicit access to a read/write state, with additional operations for pushing the current state on a stack and later restoring the state from the top of the stack.
Binding strategy:: Same as for the usual state monad; the state and accompanying stack of saved states are threaded through computations.
Useful for:: Remembering state while emitting commands for some system which itself has saveable/restorable state, such as OpenGL or Cairo.

Simple example:

ghci> let p = get >>= liftIO . print
ghci> evalStateStackT (put 2 >> p >> save >> put 3 >> p >> restore >> p) 0
2
3
2

2 types
1 class
7 values

Packagestatestack-0.3.1.1
Exports10
LanguageHaskell2010
LicenceBSD-3-Clause
SourceStateStack.hs

The `MonadStateStack` class

1 declaration

classclass MonadState s m => MonadStateStack s (m :: Type -> Type) where

Class of monads which support a state along with a stack for saving and restoring states.

Methods

save :: m ()
restore :: m ()

Instances10MonadStateStack, …

MonadStateStack s m => MonadStateStack s (MaybeT m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
Monad m => MonadStateStack s (StateStackT s m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
MonadStateStack s m => MonadStateStack s (ExceptT e m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
MonadStateStack s m => MonadStateStack s (IdentityT m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
MonadStateStack s m => MonadStateStack s (ReaderT r m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
MonadStateStack s m => MonadStateStack s (StateT s m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
MonadStateStack s m => MonadStateStack s (StateT s m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
(Monoid w, MonadStateStack s m) => MonadStateStack s (WriterT w m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
(Monoid w, MonadStateStack s m) => MonadStateStack s (WriterT w m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
MonadStateStack s m => MonadStateStack s (ContT r m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack

The `StateStackT` transformer

2 declarations

newtypenewtype StateStackT s (m :: Type -> Type) a

A monad transformer which adds a save/restorable state to an existing monad.

Constructors

StateStackT
- unStateStackT :: StateT (s, [s]) m a

Instances8MonadState, MonadStateStack, MonadTrans, Monad, Functor, Applicative, …

Monad m => MonadState s (StateStackT s m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
Monad m => MonadStateStack s (StateStackT s m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
MonadTrans (StateStackT s)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
Monad m => Monad (StateStackT s m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
Functor m => Functor (StateStackT s m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
Monad m => Applicative (StateStackT s m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
MonadIO m => MonadIO (StateStackT s m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack
MonadCont m => MonadCont (StateStackT s m)Defined in statestack-0.3.1.1 · Control.Monad.StateStack

typetype StateStack s a = StateStackT s Identity a

Running `StateStackT` and `StateStack` computations

7 declarations

valuerunStateStackT :: Monad m => StateStackT s m a -> s -> m (a, s)

Run a StateStackT computation from an initial state, resulting in a computation of the underlying monad which yields the return value and final state.

valueevalStateStackT :: Monad m => StateStackT s m a -> s -> m a

Like runStateStackT, but discard the final state.

valueexecStateStackT :: Monad m => StateStackT s m a -> s -> m s

Like runStateStackT, but discard the return value and yield only the final state.

valuerunStateStack :: StateStack s a -> s -> (a, s)

Run a StateStack computation from an initial state, resulting in a pair of the final return value and final state.

valueevalStateStack :: StateStack s a -> s -> a

Like runStateStack, but discard the final state.

valueexecStateStack :: StateStack s a -> s -> s

Like runStateStack, but discard the return value and yield only the final state.

valueliftState :: Monad m => StateT s m a -> StateStackT s m a

StateT computations can always be lifted to StateStackT computations which do not manipulate the state stack.