Control.Monad.RWS.Lazy

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

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 :: 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

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, 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)

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

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

Lazy Reader-writer-state monads

module Control.Monad.RWS.Class

module Control.Monad

module Control.Monad.Fix

module Control.Monad.Trans

module Data.Monoid