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.CPS

Contents

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

Description

Strict RWS monad that uses continuation-passing-style to achieve constant space usage.

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.

Since: mtl-2.3, transformers-0.5.6

Synopsis

type RWS r w s = RWST r w s Identity
rws :: Monoid w => (r -> s -> (a, s, w)) -> RWS r w s a
runRWS :: Monoid w => RWS r w s a -> r -> s -> (a, s, w)
evalRWS :: Monoid w => RWS r w s a -> r -> s -> (a, w)
execRWS :: Monoid w => RWS r w s a -> r -> s -> (s, w)
mapRWS :: (Monoid w, Monoid w') => ((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
data RWST r w s (m :: Type -> Type) a
runRWST :: Monoid w => RWST r w s m a -> r -> s -> m (a, s, w)
evalRWST :: (Monad m, Monoid w) => RWST r w s m a -> r -> s -> m (a, w)
execRWST :: (Monad m, Monoid w) => RWST r w s m a -> r -> s -> m (s, w)
mapRWST :: (Monad n, Monoid w, Monoid w') => (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 #

A monad containing an environment of type r, output of type w and an updatable state of type s.

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

Construct an RWS computation from a function. (The inverse of runRWS .)

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

Unwrap an RWS computation as a function. (The inverse of rws .)

evalRWS #

Arguments

:: Monoid w

=> 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 #

Arguments

:: Monoid w

=> 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 :: (Monoid w, Monoid w') => ((a, s, w) -> (b, s, w')) -> RWS r w s a -> RWS r w' s b #

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 #

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

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

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.

Instances

Instances details

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

Since: 2.3

Instance details

Defined in Control.Monad.RWS.Class

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

Since: 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 #

Since: 2.3

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 #

Since: 2.3

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 => 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: 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 #

Since: 2.3

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 #

Since: 2.3

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 #

MonadTrans (RWST r w s)

Instance details

Defined in Control.Monad.Trans.RWS.CPS

Methods

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

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

Instance details

Defined in Control.Monad.Trans.RWS.CPS

Methods

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

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

Instance details

Defined in Control.Monad.Trans.RWS.CPS

Methods

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

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

Instance details

Defined in Control.Monad.Trans.RWS.CPS

Methods

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

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

Instance details

Defined in Control.Monad.Trans.RWS.CPS

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] #

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

Instance details

Defined in Control.Monad.Trans.RWS.CPS

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.CPS

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 #

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

Instance details

Defined in Control.Monad.Trans.RWS.CPS

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 #

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

Instance details

Defined in Control.Monad.Trans.RWS.CPS

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

Since: 2.3

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 #

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

Unwrap an RWST computation as a function. (The inverse of rwsT .)

evalRWST #

Arguments

:: (Monad m, Monoid w)

=> 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 #

Arguments

:: (Monad m, Monoid w)

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

Map the inner computation using the given function.

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

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)

Strict Reader-writer-state monads

module Control.Monad.RWS.Class

module Control.Monad.Trans