Control.Monad.State.Class

MonadState class.

This module is inspired by the paper /Functional Programming with Overloading and Higher-Order Polymorphism/, Mark P Jones (http://www.cse.ogi.edu/~mpj/) Advanced School of Functional Programming, 1995.

MonadState class

class Monad m => MonadState m where

get returns the state from the internals of the monad.

put replaces the state inside the monad.

Minimal complete definition

get, put

Associated Types

type StateType m

Methods

get :: m (StateType m)

put :: StateType m -> m ()

Instances

(Monoid w, MonadState m) => MonadState (WriterT w m)

Associated Types

type StateType (WriterT w m :: * -> *) :: *

Methods

get :: WriterT w m (StateType (WriterT w m))

put :: StateType (WriterT w m) -> WriterT w m ()

(Monoid w, MonadState m) => MonadState (WriterT w m)

Associated Types

type StateType (WriterT w m :: * -> *) :: *

Methods

get :: WriterT w m (StateType (WriterT w m))

put :: StateType (WriterT w m) -> WriterT w m ()

Monad m => MonadState (StateT s m)

Associated Types

type StateType (StateT s m :: * -> *) :: *

Methods

get :: StateT s m (StateType (StateT s m))

put :: StateType (StateT s m) -> StateT s m ()

Monad m => MonadState (StateT s m)

Associated Types

type StateType (StateT s m :: * -> *) :: *

Methods

get :: StateT s m (StateType (StateT s m))

put :: StateType (StateT s m) -> StateT s m ()

MonadState m => MonadState (ExceptT e m)

Associated Types

type StateType (ExceptT e m :: * -> *) :: *

Methods

get :: ExceptT e m (StateType (ExceptT e m))

put :: StateType (ExceptT e m) -> ExceptT e m ()

MonadState m => MonadState (ReaderT * r m)

Associated Types

type StateType (ReaderT * r m :: * -> *) :: *

Methods

get :: ReaderT * r m (StateType (ReaderT * r m))

put :: StateType (ReaderT * r m) -> ReaderT * r m ()

MonadState m => MonadState (ContT * r m)

Associated Types

type StateType (ContT * r m :: * -> *) :: *

Methods

get :: ContT * r m (StateType (ContT * r m))

put :: StateType (ContT * r m) -> ContT * r m ()

(Monoid w, Monad m) => MonadState (RWST r w s m)

Associated Types

type StateType (RWST r w s m :: * -> *) :: *

Methods

get :: RWST r w s m (StateType (RWST r w s m))

put :: StateType (RWST r w s m) -> RWST r w s m ()

(Monoid w, Monad m) => MonadState (RWST r w s m)

Associated Types

type StateType (RWST r w s m :: * -> *) :: *

Methods

get :: RWST r w s m (StateType (RWST r w s m))

put :: StateType (RWST r w s m) -> RWST r w s m ()

modify :: MonadState m => (StateType m -> StateType m) -> m ()

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.

gets :: MonadState m => (StateType m -> a) -> m a

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