transformers-0.2.2.0: Concrete functor and monad transformersSource codeContentsIndex
Control.Monad.Trans.RWS.Strict
Portabilityportable
Stabilityexperimental
Maintainerross@soi.city.ac.uk
Contents
The RWS monad
The RWST monad transformer
Reader operations
Writer operations
State operations
Lifting other operations
Description
A monad transformer that combines ReaderT, WriterT and StateT. This version is strict; for a lazy version, see Control.Monad.Trans.RWS.Lazy, which has the same interface.
Synopsis
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
newtype RWST r w s m a = RWST {
runRWST :: r -> s -> m (a, s, w)
}
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
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
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)
listens :: (Monoid w, Monad m) => (w -> b) -> RWST r w s m a -> RWST r w s m (a, b)
pass :: (Monoid w, Monad m) => RWST r w s m (a, w -> w) -> RWST r w s m a
censor :: (Monoid w, Monad m) => (w -> w) -> RWST r w s m a -> RWST r w s m a
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 ()
gets :: (Monoid w, Monad m) => (s -> a) -> RWST r w s m a
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
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
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
The RWS monad
type RWS r w s = RWST r w s IdentitySource
A monad containing an environment of type r, output of type w and an updatable state of type s.
rws :: (r -> s -> (a, s, w)) -> RWS r w s aSource
Construct an RWS computation from a function. (The inverse of runRWS.)
runRWS :: RWS r w s a -> r -> s -> (a, s, w)Source
Unwrap an RWS computation as a function. (The inverse of rws.)
evalRWS :: RWS r w s a -> r -> s -> (a, w)Source
execRWS :: RWS r w s a -> r -> s -> (s, w)Source
mapRWS :: ((a, s, w) -> (b, s, w')) -> RWS r w s a -> RWS r w' s bSource
withRWS :: (r' -> s -> (r, s)) -> RWS r w s a -> RWS r' w s aSource
The RWST monad transformer
newtype RWST r w s m a Source
A monad transformer adding reading an environment of type r, collecting an output of type w and updating a state of type s to an inner monad m.
Constructors
RWST
runRWST :: r -> s -> m (a, s, w)
show/hide 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)Source
execRWST :: Monad m => RWST r w s m a -> r -> s -> m (s, w)Source
mapRWST :: (m (a, s, w) -> n (b, s, w')) -> RWST r w s m a -> RWST r w' s n bSource
withRWST :: (r' -> s -> (r, s)) -> RWST r w s m a -> RWST r' w s m aSource
Reader operations
ask :: (Monoid w, Monad m) => RWST r w s m rSource
Fetch the value of the environment.
local :: (Monoid w, Monad m) => (r -> r) -> RWST r w s m a -> RWST r w s m aSource
Execute a computation in a modified environment
asks :: (Monoid w, Monad m) => (r -> a) -> RWST r w s m aSource
Retrieve a function of the current environment.
Writer operations
tell :: (Monoid w, Monad m) => w -> RWST r w s m ()Source
tell w is an action that produces the output w.
listen :: (Monoid w, Monad m) => RWST r w s m a -> RWST r w s m (a, w)Source
listen m is an action that executes the action m and adds its output to the value of the computation.
listens :: (Monoid w, Monad m) => (w -> b) -> RWST r w s m a -> RWST r w s m (a, b)Source

listens f m is an action that executes the action m and adds the result of applying f to the output to the value of the computation.

pass :: (Monoid w, Monad m) => RWST r w s m (a, w -> w) -> RWST r w s m aSource
pass m is an action that executes the action m, which returns a value and a function, and returns the value, applying the function to the output.
censor :: (Monoid w, Monad m) => (w -> w) -> RWST r w s m a -> RWST r w s m aSource

censor f m is an action that executes the action m and applies the function f to its output, leaving the return value unchanged.

State operations
get :: (Monoid w, Monad m) => RWST r w s m sSource
Fetch the current value of the state within the monad.
put :: (Monoid w, Monad m) => s -> RWST r w s m ()Source
put s sets the state within the monad to s.
modify :: (Monoid w, Monad m) => (s -> s) -> RWST r w s m ()Source
modify f is an action that updates the state to the result of applying f to the current state.
gets :: (Monoid w, Monad m) => (s -> a) -> RWST r w s m aSource

Get a 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 aSource
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 aSource
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 aSource
Lift a catchError operation to the new monad.
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