writer-cps-transformers-0.1.1.2: WriteT and RWST monad transformers

Copyright (c) Daniel Mendler 2016(c) Andy Gill 2001(c) Oregon Graduate Institute of Science and Technology 2001 BSD-style (see the file LICENSE) mail@daniel-mendler.de experimental portable Safe Haskell2010

Control.Monad.Trans.RWS.CPS.Internal

Description

A monad transformer that combines ReaderT, WriterT and StateT. This version uses continuation-passing-style for the writer part to achieve constant space usage. This transformer can be used as a drop-in replacement for 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 :: Monoid w => (r -> s -> (a, s, w)) -> RWS r w s a Source #

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

runRWS :: Monoid w => RWS r w s a -> r -> s -> (a, s, w) Source #

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

Arguments

 :: Monoid w => 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.

Arguments

 :: Monoid w => 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 :: (Monoid w, Monoid w') => ((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.

• runRWS (mapRWS f m) r s = f (runRWS m r s)

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.

• runRWS (withRWS f m) r s = uncurry (runRWS m) (f r s)

# 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 FieldsunRWST :: r -> s -> w -> m (a, s, w)

Instances

 MonadTrans (RWST r w s) Source # Methodslift :: Monad m => m a -> RWST r w s m a # 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 # Methodsfmap :: (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 # MonadFix m => MonadFix (RWST r w s m) Source # Methodsmfix :: (a -> RWST r w s m a) -> RWST r w s m a # MonadFail m => MonadFail (RWST r w s m) Source # Methodsfail :: String -> RWST r w s m a # (Functor m, Monad m) => Applicative (RWST r w s m) Source # Methodspure :: 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 # MonadIO m => MonadIO (RWST r w s m) Source # MethodsliftIO :: IO a -> RWST r w s m a # (Functor m, MonadPlus m) => Alternative (RWST r w s m) Source # Methodsempty :: 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] # (Functor m, MonadPlus m) => MonadPlus (RWST r w s m) Source # Methodsmzero :: 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 #

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

The RWST constructor is deliberately not exported in the CPS module to avoid exposing the hidden state w. rwsT provides a safe way to construct a RWST with the same api as the original RWST.

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

Unwrap an RWST computation as a function.

Arguments

 :: (Monad m, Monoid w) => 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.

Arguments

 :: (Monad m, Monoid w) => 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 :: (Monad n, Monoid w, Monoid w') => (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.

• runRWST (mapRWST f m) r s = f (runRWST m r s) 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 Source #

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

• runRWST (withRWST f m) r s = uncurry (runRWST m) (f r s)

# Reader operations

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

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

ask :: 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

• runRWST (local f m) r s = runRWST m (f r) s

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

Retrieve a function of the current environment.

• asks f = liftM f ask

# Writer operations

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

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

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

tell w is an action that produces the output w.

listen :: (Monoid w, 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.

• runRWST (listen m) r s = liftM (\ (a, w) -> ((a, w), w)) (runRWST m r s)

listens :: (Monoid w, 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.

• listens f m = liftM (id *** f) (listen m)
• runRWST (listens f m) r s = liftM (\ (a, w) -> ((a, f w), w)) (runRWST m r s)

pass :: (Monoid w, Monoid w', 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.

• runRWST (pass m) r s = liftM (\ ((a, f), w) -> (a, f w)) (runRWST m r s)

censor :: (Monoid w, 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.

• censor f m = pass (liftM (\ x -> (x,f)) m)
• runRWST (censor f m) r s = liftM (\ (a, w) -> (a, f w)) (runRWST m r s)

# State operations

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

Construct a state monad computation from a state transformer function.

get :: Monad m => RWST r w s m s Source #

Fetch the current value of the state within the monad.

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

put s sets the state within the monad to s.

modify :: 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.

• modify f = get >>= (put . f)

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

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

• gets f = liftM f get

# Lifting other operations

liftCallCC :: 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' :: 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.