Control.Monad.RSS.Lazy

Lazy RSS monad.

This is a variant of the classic "Control.Monad..RWS.Lazy" transformer, where the Writer part rides with the State part.

The RSS monad

type RSS r w s = RSST r w s Identity

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

rss :: Monoid w => (r -> s -> (a, s, w)) -> RSS r w s a

Construct an RSS computation from a function. (The inverse of runRSS.)

runRSS :: Monoid w => RSS r w s a -> r -> s -> (a, s, w)

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

evalRSS

Arguments

:: Monoid w

=> RSS 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.

execRSS

Arguments

:: Monoid w

=> RSS 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.

withRSS :: (r' -> s -> (r, s)) -> RSS r w s a -> RSS r' w s a

The RSST monad transformer

data RSST 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.

Instances

(Monoid w, Monad m) => MonadRWS r w s (RSST r w s m)

Monad m => MonadState s (RSST r w s m)

Monad m => MonadReader r (RSST r w s m)

(Monoid w, Monad m) => MonadWriter w (RSST r w s m)

MonadTrans (RSST r w s)

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

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

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

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

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

MonadPlus m => MonadPlus (RSST r w s m)

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

evalRSST

Arguments

:: (Monad m, Monoid w)

=> RSST 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.

execRSST

Arguments

:: (Monad m, Monoid w)

=> RSST 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.

withRSST :: (r' -> s -> (r, s)) -> RSST r w s m a -> RSST r' w s m a

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

• runRSST (withRSST f m) r s = uncurry (runRSST m) (f r s)

Lazy Reader-writer-state monads

module Control.Monad

module Control.Monad.Fix

module Data.Monoid