mtl-2.2.1: Monad classes, using functional dependencies

Copyright(c) Andy Gill 2001, (c) Oregon Graduate Institute of Science and Technology, 2001
LicenseBSD-style (see the file LICENSE)
Maintainerlibraries@haskell.org
Stabilityexperimental
Portabilitynon-portable (multi-param classes, functional dependencies)
Safe HaskellSafe-Inferred
LanguageHaskell98

Control.Monad.RWS.Strict

Contents

Description

Strict 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

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

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

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

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

evalRWS

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

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

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

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 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.

Constructors

RWST 

Fields

runRWST :: r -> s -> m (a, s, w)
 

Instances

(Monoid w, Monad m) => MonadRWS r w s (RWST r w s m) 
(Monoid w, Monad m) => MonadWriter w (RWST r w s m) 
(Monad m, Monoid w) => MonadState s (RWST r w s m) 
(Monad m, Monoid w) => MonadReader r (RWST r w s m) 
(Monoid w, MonadError e m) => MonadError e (RWST r w s m) 
Monoid w => MonadTrans (RWST r w s) 
(Monoid w, Functor m, MonadPlus m) => Alternative (RWST r w s m) 
(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, MonadIO m) => MonadIO (RWST r w s m) 
(Monoid w, MonadCont m) => MonadCont (RWST r w s m) 

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

evalRWST

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

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

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

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

Strict Reader-writer-state monads