Control.Monad.State.Class · mtl-2.3.2

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

Source#

Minimal definition is either both of get and put or just state

Methods

get :: m s
Return the state from the internals of the monad.
put :: s -> m ()
Replace the state inside the monad.
state :: (s -> (a, s)) -> m a
Embed a simple state action into the monad.

Instances16MonadState, …

MonadState s m => MonadState s (MaybeT m)Defined in mtl-2.3.2 · Control.Monad.State.Class
Monad m => MonadState s (StateT s m)Defined in mtl-2.3.2 · Control.Monad.State.Class
Monad m => MonadState s (StateT s m)Defined in mtl-2.3.2 · Control.Monad.State.Class
MonadState s m => MonadState s (ExceptT e m)Defined in mtl-2.3.2 · Control.Monad.State.Class
MonadState s m => MonadState s (IdentityT m)Defined in mtl-2.3.2 · Control.Monad.State.Class
MonadState s m => MonadState s (ReaderT r m)Defined in mtl-2.3.2 · Control.Monad.State.Class
MonadState s m => MonadState s (SelectT r m)Defined in mtl-2.3.2 · Control.Monad.State.Class
(Monoid w, MonadState s m) => MonadState s (AccumT w m)Defined in mtl-2.3.2 · Control.Monad.State.Class
(Monoid w, MonadState s m) => MonadState s (WriterT w m)Defined in mtl-2.3.2 · Control.Monad.State.Class
(Monoid w, MonadState s m) => MonadState s (WriterT w m)Defined in mtl-2.3.2 · Control.Monad.State.Class
(Monoid w, MonadState s m) => MonadState s (WriterT w m)Defined in mtl-2.3.2 · Control.Monad.State.Class
MonadState s m => MonadState s (ContT r m)Defined in mtl-2.3.2 · Control.Monad.State.Class
(MonadState s m, MonadState s n) => MonadState s (Product m n)Defined in mtl-2.3.2 · Control.Monad.State.Class
(Monad m, Monoid w) => MonadState s (RWST r w s m)Defined in mtl-2.3.2 · Control.Monad.State.Class
(Monad m, Monoid w) => MonadState s (RWST r w s m)Defined in mtl-2.3.2 · Control.Monad.State.Class
(Monad m, Monoid w) => MonadState s (RWST r w s m)Defined in mtl-2.3.2 · Control.Monad.State.Class

valuemodify :: MonadState s m => (s -> s) -> m ()

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Monadic state transformer.

Maps an old state to a new state inside a state monad. The old state is thrown away.

     Main> :t modify ((+1) :: Int -> Int)
     modify (...) :: (MonadState Int a) => a ()

This says that modify (+1) acts over any Monad that is a member of the MonadState class, with an Int state.

valuemodify' :: MonadState s m => (s -> s) -> m ()

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A variant of modify in which the computation is strict in the new state.

valuegets :: MonadState s m => (s -> a) -> m a

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Gets specific component of the state, using a projection function supplied.