transformers-0.5.5.0: Concrete functor and monad transformers

Copyright(c) Andy Gill 2001
(c) Oregon Graduate Institute of Science and Technology 2001
LicenseBSD-style (see the file LICENSE)
MaintainerR.Paterson@city.ac.uk
Stabilityexperimental
Portabilityportable
Safe HaskellSafe
LanguageHaskell98

Control.Monad.Trans.RWS.Lazy

Contents

Description

A monad transformer that combines ReaderT, WriterT and StateT. This version is lazy; for a strict version with the same interface, see Control.Monad.Trans.RWS.Strict.

Synopsis

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 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 

Fields

Instances

Monoid w => MonadTrans (RWST r w s) Source # 

Methods

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

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

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 #

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

Functor m => Functor (RWST r w s m) Source # 

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 #

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

Methods

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

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

Methods

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

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

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 #

(*>) :: 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 #

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

Methods

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

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

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] #

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

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 #

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.

Reader operations

reader :: (Monoid w, Monad m) => (r -> a) -> RWST r w s m a Source #

Constructor for computations in the reader monad (equivalent to asks).

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

Fetch the value of the environment.

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

Execute a computation in a modified environment

asks :: (Monoid w, Monad m) => (r -> a) -> RWST r w s m a Source #

Retrieve a function of the current environment.

Writer operations

writer :: Monad m => (a, w) -> RWST r w s m a Source #

Construct a writer computation from a (result, output) pair.

tell :: Monad m => w -> RWST r w s m () Source #

tell w is an action that produces the output w.

listen :: Monad m => RWST r w s m a -> RWST r w s m (a, w) Source #

listen m is an action that executes the action m and adds its output to the value of the computation.

listens :: Monad m => (w -> b) -> RWST r w s m a -> RWST r w s m (a, b) Source #

listens f m is an action that executes the action m and adds the result of applying f to the output to the value of the computation.

pass :: Monad m => RWST r w s m (a, w -> w) -> RWST r w s m a Source #

pass m is an action that executes the action m, which returns a value and a function, and returns the value, applying the function to the output.

censor :: Monad m => (w -> w) -> RWST r w s m a -> RWST r w s m a Source #

censor f m is an action that executes the action m and applies the function f to its output, leaving the return value unchanged.

State operations

state :: (Monoid w, Monad m) => (s -> (a, s)) -> RWST r w s m a Source #

Construct a state monad computation from a state transformer function.

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

Fetch the current value of the state within the monad.

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

put s sets the state within the monad to s.

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

modify f is an action that updates the state to the result of applying f to the current state.

gets :: (Monoid w, Monad m) => (s -> a) -> RWST r w s m a Source #

Get a specific component of the state, using a projection function supplied.

Lifting other operations

liftCallCC :: Monoid w => CallCC m (a, s, w) (b, s, w) -> CallCC (RWST r w s m) a b Source #

Uniform lifting of a callCC operation to the new monad. This version rolls back to the original state on entering the continuation.

liftCallCC' :: Monoid w => CallCC m (a, s, w) (b, s, w) -> CallCC (RWST r w s m) a b Source #

In-situ lifting of a callCC operation to the new monad. This version uses the current state on entering the continuation.

liftCatch :: Catch e m (a, s, w) -> Catch e (RWST r w s m) a Source #

Lift a catchE operation to the new monad.