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.RWS.Lazy

Contents

The RWS monad
The RWST monad transformer
Lazy Reader-writer-state monads

Description

Lazy RWS monad.

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

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 :: Type -> Type) a = RWST (r -> s -> m (a, s, w))
runRWST :: RWST r w s m a -> 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 :: forall r' s r w (m :: Type -> Type) a. (r' -> s -> (r, s)) -> RWST r w s m a -> RWST r' w s m a
module Control.Monad.RWS.Class
module Control.Monad.Trans

The RWS monad

type RWS r w s = RWST r w s Identity Source #

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 a Source #

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 Source #

Arguments

:: RWS r w s a	RWS computation to execute
-> r	initial environment
-> s	initial value
-> (a, w)	final value and output

Evaluate a computation with the given initial state and environment, returning the final value and output, discarding the final state.

execRWS Source #

Arguments

:: RWS r w s a	RWS computation to execute
-> r	initial environment
-> s	initial value
-> (s, w)	final state and output

Evaluate a computation with the given initial state and environment, returning the final state and output, discarding the final value.

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

Map the return value, final state and output of a computation using the given function.

runRWS (mapRWS f m) r s = f (runRWS m r s)

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

withRWS f m executes action m with an initial environment and state modified by applying f.

runRWS (withRWS f m) r s = uncurry (runRWS m) (f r s)

The RWST monad transformer

newtype RWST r w s (m :: Type -> Type) 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 (r -> s -> m (a, s, w))

Instances

Instances details

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

Instance details

Defined in Control.Monad.RWS.Class

(MonadAccum w' m, Monoid w) => MonadAccum w' (RWST r w s m) Source #

Since: mtl-2.3

Instance details

Defined in Control.Monad.Accum

Methods

look :: RWST r w s m w' Source #

add :: w' -> RWST r w s m () Source #

accum :: (w' -> (a, w')) -> RWST r w s m a Source #

(Monoid w, MonadError e m) => MonadError e (RWST r w s m) Source #

Instance details

Defined in Control.Monad.Error.Class

Methods

throwError :: e -> RWST r w s m a Source #

catchError :: RWST r w s m a -> (e -> RWST r w s m a) -> RWST r w s m a Source #

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

Instance details

Defined in Control.Monad.Reader.Class

Methods

ask :: RWST r w s m r Source #

local :: (r -> r) -> RWST r w s m a -> RWST r w s m a Source #

reader :: (r -> a) -> RWST r w s m a Source #

(MonadSelect w' m, Monoid w) => MonadSelect w' (RWST r w s m) Source #

A combination of an 'outer' ReaderT, WriterT and StateT. In short, you get a value of type r which can influence what gets picked, but not how anything is ranked, and the 'ranking' function gets access to an s and a w, but can modify neither.

Since: mtl-2.3

Instance details

Defined in Control.Monad.Select

Methods

select :: ((a -> w') -> a) -> RWST r w s m a Source #

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

Instance details

Defined in Control.Monad.State.Class

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 #

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

Instance details

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> RWST r w s m a Source #

tell :: w -> RWST r w s m () Source #

listen :: RWST r w s m a -> RWST r w s m (a, w) Source #

pass :: RWST r w s m (a, w -> w) -> RWST r w s m a Source #

Monoid w => MonadTrans (RWST r w s)

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

lift :: Monad m => m a -> RWST r w s m a Source #

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

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

liftIO :: IO a -> RWST r w s m a Source #

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

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

contramap :: (a' -> a) -> RWST r w s m a -> RWST r w s m a' Source #

(>$) :: b -> RWST r w s m b -> RWST r w s m a Source #

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

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

empty :: RWST r w s m a #

(<|>) :: RWST r w s m a -> RWST r w s m a -> RWST r w s m a #

some :: RWST r w s m a -> RWST r w s m [a] #

many :: RWST r w s m a -> RWST r w s m [a] #

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

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

pure :: a -> RWST r w s m a #

(<*>) :: RWST r w s m (a -> b) -> RWST r w s m a -> RWST r w s m b #

liftA2 :: (a -> b -> c) -> RWST r w s m a -> RWST r w s m b -> RWST r w s m c #

(*>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b #

(<*) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m a #

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

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

fmap :: (a -> b) -> RWST r w s m a -> RWST r w s m b #

(<$) :: a -> RWST r w s m b -> RWST r w s m a #

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

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

(>>=) :: RWST r w s m a -> (a -> RWST r w s m b) -> RWST r w s m b #

(>>) :: RWST r w s m a -> RWST r w s m b -> RWST r w s m b #

return :: a -> RWST r w s m a #

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

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

mzero :: RWST r w s m a #

mplus :: RWST r w s m a -> RWST r w s m a -> RWST r w s m a #

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

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

fail :: String -> RWST r w s m a #

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

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

mfix :: (a -> RWST r w s m a) -> RWST r w s m a #

(Monoid w, MonadCont m) => MonadCont (RWST r w s m) Source #

Instance details

Defined in Control.Monad.Cont.Class

Methods

callCC :: ((a -> RWST r w s m b) -> RWST r w s m a) -> RWST r w s m a Source #

Generic (RWST r w s m a)

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Associated Types

type Rep (RWST r w s m a)
Instance details Defined in Control.Monad.Trans.RWS.Lazy type Rep (RWST r w s m a) = D1 ('MetaData "RWST" "Control.Monad.Trans.RWS.Lazy" "transformers-0.6.1.1-2aba" 'True) (C1 ('MetaCons "RWST" 'PrefixI 'True) (S1 ('MetaSel ('Just "runRWST") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (r -> s -> m (a, s, w)))))

Methods

from :: RWST r w s m a -> Rep (RWST r w s m a) x #

to :: Rep (RWST r w s m a) x -> RWST r w s m a #

type Rep (RWST r w s m a)

Instance details

Defined in Control.Monad.Trans.RWS.Lazy

type Rep (RWST r w s m a) = D1 ('MetaData "RWST" "Control.Monad.Trans.RWS.Lazy" "transformers-0.6.1.1-2aba" 'True) (C1 ('MetaCons "RWST" 'PrefixI 'True) (S1 ('MetaSel ('Just "runRWST") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (r -> s -> m (a, s, w)))))

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

evalRWST Source #

Arguments

:: Monad m
=> RWST r w s m a	computation to execute
-> r	initial environment
-> s	initial value
-> m (a, w)	computation yielding final value and output

Evaluate a computation with the given initial state and environment, returning the final value and output, discarding the final state.

execRWST Source #

Arguments

:: Monad m
=> RWST r w s m a	computation to execute
-> r	initial environment
-> s	initial value
-> m (s, w)	computation yielding final state and output

Evaluate a computation with the given initial state and environment, returning the final state and output, discarding the final value.

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

Map the inner computation using the given function.

runRWST (mapRWST f m) r s = f (runRWST m r s)

withRWST :: forall r' s r w (m :: Type -> Type) a. (r' -> s -> (r, s)) -> RWST r w s m a -> RWST r' w s m a Source #

withRWST f m executes action m with an initial environment and state modified by applying f.

runRWST (withRWST f m) r s = uncurry (runRWST m) (f r s)

Lazy Reader-writer-state monads

module Control.Monad.RWS.Class

module Control.Monad.Trans