Copyright	(c) Andy Gill 2001 (c) Oregon Graduate Institute of Science and Technology 2001
License	BSD-style (see the file LICENSE)
Maintainer	libraries@haskell.org
Stability	experimental
Portability	non-portable (multi-param classes, functional dependencies)
Safe Haskell	Safe
Language	Haskell2010

Control.Monad.State.Class

Description

MonadState class.

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

Synopsis

class Monad m => MonadState s m | m -> s where
modify :: MonadState s m => (s -> s) -> m ()
modify' :: MonadState s m => (s -> s) -> m ()
gets :: MonadState s m => (s -> a) -> m a

Documentation

class Monad m => MonadState s m | m -> s where Source #

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

Minimal complete definition

state | get, put

Methods

get :: m s Source #

Return the state from the internals of the monad.

put :: s -> m () Source #

Replace the state inside the monad.

state :: (s -> (a, s)) -> m a Source #

Embed a simple state action into the monad.

Instances

MonadState s m => MonadState s (MaybeT m) Source #
Instance details Methods get :: MaybeT m s Source # put :: s -> MaybeT m () Source # state :: (s -> (a, s)) -> MaybeT m a Source #
MonadState s m => MonadState s (ListT m) Source #
Instance details Methods get :: ListT m s Source # put :: s -> ListT m () Source # state :: (s -> (a, s)) -> ListT m a Source #
(Monoid w, MonadState s m) => MonadState s (WriterT w m) Source #
Instance details Methods get :: WriterT w m s Source # put :: s -> WriterT w m () Source # state :: (s -> (a, s)) -> WriterT w m a Source #
(Monoid w, MonadState s m) => MonadState s (WriterT w m) Source #
Instance details Methods get :: WriterT w m s Source # put :: s -> WriterT w m () Source # state :: (s -> (a, s)) -> WriterT w m a Source #
MonadState s m => MonadState s (IdentityT m) Source #
Instance details Methods get :: IdentityT m s Source # put :: s -> IdentityT m () Source # state :: (s -> (a, s)) -> IdentityT m a Source #
MonadState s m => MonadState s (ExceptT e m) Source #
Instance details Methods get :: ExceptT e m s Source # put :: s -> ExceptT e m () Source # state :: (s -> (a, s)) -> ExceptT e m a Source #
(Error e, MonadState s m) => MonadState s (ErrorT e m) Source #
Instance details Methods get :: ErrorT e m s Source # put :: s -> ErrorT e m () Source # state :: (s -> (a, s)) -> ErrorT e m a Source #
Monad m => MonadState s (StateT s m) Source #
Instance details Methods get :: StateT s m s Source # put :: s -> StateT s m () Source # state :: (s -> (a, s)) -> StateT s m a Source #
Monad m => MonadState s (StateT s m) Source #
Instance details Methods get :: StateT s m s Source # put :: s -> StateT s m () Source # state :: (s -> (a, s)) -> StateT s m a Source #
MonadState s m => MonadState s (ReaderT r m) Source #
Instance details Methods get :: ReaderT r m s Source # put :: s -> ReaderT r m () Source # state :: (s -> (a, s)) -> ReaderT r m a Source #
MonadState s m => MonadState s (ContT r m) Source #
Instance details Methods get :: ContT r m s Source # put :: s -> ContT r m () Source # state :: (s -> (a, s)) -> ContT r m a Source #
(Monad m, Monoid w) => MonadState s (RWST r w s m) Source #
Instance details Methods get :: RWST r w s m s Source # put :: s -> RWST r w s m () Source # state :: (s -> (a, s)) -> RWST r w s m a Source #
(Monad m, Monoid w) => MonadState s (RWST r w s m) Source #
Instance details Methods get :: RWST r w s m s Source # put :: s -> RWST r w s m () Source # state :: (s -> (a, s)) -> RWST r w s m a Source #

modify :: MonadState s m => (s -> s) -> m () Source #

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.

modify' :: MonadState s m => (s -> s) -> m () Source #

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

gets :: MonadState s m => (s -> a) -> m a Source #

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