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

Contents

The MonadStateStack class
The StateStackT transformer
Running StateStackT and StateStack computations

Synopsis

class MonadStateStack
newtype StateStackT
type StateStack
value runStateStackT
value evalStateStackT
value execStateStackT
value runStateStack
value evalStateStack
value execStateStack
value liftState

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

The `MonadStateStack` class

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

Source#

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

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

Source#

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

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

Source#

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