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Control.Monad.RWS.Lazy

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

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.

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.

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.

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

Defined in Control.Monad.RWS.Class

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

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

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

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

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

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 Source

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

(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 Source

(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 Source

(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 Source

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

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

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

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

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

(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 Source

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

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

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

(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 Source

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

(Monoid w, MonadCont m) => MonadCont (RWST r w s m)
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 :: 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.

withRWST :: (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.

Lazy Reader-writer-state monads

module Control.Monad.RWS.Class

module Control.Monad

module Control.Monad.Fix

module Control.Monad.Trans

module Data.Monoid

© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.6.1/docs/html/libraries/mtl-2.2.2/Control-Monad-RWS-Lazy.html