Control.Monad.Trans.RWS.Lazy

Lazy RWS monad.

The RWS monad

type RWS r w s = RWST r w s Identity

rws :: (r -> s -> (a, s, w)) -> RWS r w s a

runRWS :: RWS r w s a -> r -> s -> (a, s, w)

evalRWS :: RWS r w s a -> r -> s -> (a, w)

execRWS :: RWS r w s a -> r -> s -> (s, w)

mapRWS :: ((a, s, w) -> (b, s, w')) -> RWS r w s a -> RWS r w' s b

withRWS :: (r' -> s -> (r, s)) -> RWS r w s a -> RWS r' w s a

The RWST monad transformer

newtype RWST r w s m a

Constructors

RWST

Fields

runRWST :: r -> s -> m (a, s, w)

Instances

Monoid w => MonadTrans (RWST r w s)

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

Functor m => Functor (RWST r w s m)

(Monoid w, MonadFix m) => MonadFix (RWST r w s m)

(Monoid w, MonadPlus m) => MonadPlus (RWST r w s m)

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

(Monoid w, Functor m, MonadPlus m) => Alternative (RWST r w s m)

(Monoid w, MonadIO m) => MonadIO (RWST r w s m)

evalRWST :: Monad m => RWST r w s m a -> r -> s -> m (a, w)

execRWST :: Monad m => RWST r w s m a -> r -> s -> m (s, w)

mapRWST :: (m (a, s, w) -> n (b, s, w')) -> RWST r w s m a -> RWST r w' s n b

withRWST :: (r' -> s -> (r, s)) -> RWST r w s m a -> RWST r' w s m a

Reader operations

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

local :: (Monoid w, Monad m) => (r -> r) -> RWST r w s m a -> RWST r w s m a

asks :: (Monoid w, Monad m) => (r -> a) -> RWST r w s m a

Writer operations

tell :: (Monoid w, Monad m) => w -> RWST r w s m ()

listen :: (Monoid w, Monad m) => RWST r w s m a -> RWST r w s m (a, w)

pass :: (Monoid w, Monad m) => RWST r w s m (a, w -> w) -> RWST r w s m a

listens :: (Monoid w, Monad m) => (w -> b) -> RWST r w s m a -> RWST r w s m (a, b)

censor :: (Monoid w, Monad m) => (w -> w) -> RWST r w s m a -> RWST r w s m a

State operations

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

put :: (Monoid w, Monad m) => s -> RWST r w s m ()

modify :: (Monoid w, Monad m) => (s -> s) -> RWST r w s m ()

Monadic state transformer.

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

gets :: (Monoid w, Monad m) => (s -> a) -> RWST r w s m a

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

Lifting other operations

liftCallCC :: Monoid w => ((((a, s, w) -> m (b, s, w)) -> m (a, s, w)) -> m (a, s, w)) -> ((a -> RWST r w s m b) -> RWST r w s m a) -> RWST r w s m a

Uniform lifting of a callCC operation to the new monad. This version rolls back to the original state on entering the continuation.

liftCallCC' :: Monoid w => ((((a, s, w) -> m (b, s, w)) -> m (a, s, w)) -> m (a, s, w)) -> ((a -> RWST r w s m b) -> RWST r w s m a) -> RWST r w s m a

In-situ lifting of a callCC operation to the new monad. This version uses the current state on entering the continuation.

liftCatch :: (m (a, s, w) -> (e -> m (a, s, w)) -> m (a, s, w)) -> RWST l w s m a -> (e -> RWST l w s m a) -> RWST l w s m a

Lift a catchError operation to the new monad.