Control.Monad.Trans.MSF.Reader

MSFs with a Reader monadic layer.

This module contains functions to work with MSFs that include a Reader monadic layer. This includes functions to create new MSFs that include an additional layer, and functions to flatten that layer out of the MSF's transformer stack.

Documentation

mapReader :: (a -> b) -> Reader r a -> Reader r b

Transform the value returned by a Reader.

• runReader (mapReader f m) = f . runReader m

mapReaderT :: (m a -> n b) -> ReaderT r m a -> ReaderT r n b

Transform the computation inside a ReaderT.

• runReaderT (mapReaderT f m) = f . runReaderT m

runReader

Arguments

:: Reader r a

A Reader to run.

-> r

An initial environment.

-> a

Runs a Reader and extracts the final value from it. (The inverse of reader.)

withReader

Arguments

:: (r' -> r)

The function to modify the environment.

-> Reader r a

Computation to run in the modified environment.

-> Reader r' a

Execute a computation in a modified environment (a specialization of withReaderT).

• runReader (withReader f m) = runReader m . f

withReaderT

Arguments

:: forall r' r (m :: Type -> Type) a. (r' -> r)

The function to modify the environment.

-> ReaderT r m a

Computation to run in the modified environment.

-> ReaderT r' m a

Execute a computation in a modified environment (a more general version of local).

• runReaderT (withReaderT f m) = runReaderT m . f

type Reader r = ReaderT r Identity

The parameterizable reader monad.

Computations are functions of a shared environment.

The return function ignores the environment, while >>= passes the inherited environment to both subcomputations.

newtype ReaderT r (m :: Type -> Type) a

The reader monad transformer, which adds a read-only environment to the given monad.

The return function ignores the environment, while >>= passes the inherited environment to both subcomputations.

Constructors

ReaderT

Fields

• runReaderT :: r -> m a

Instances

MonadSplit g m => MonadSplit g (ReaderT r m)

Defined in Control.Monad.Random.Class

Methods

getSplit :: ReaderT r m g

MonadBase b m => MonadBase b (ReaderT r m)

Defined in Control.Monad.Base

Methods

liftBase :: b α -> ReaderT r m α

MonadTrans (ReaderT r)

Defined in Control.Monad.Trans.Reader

Methods

lift :: Monad m => m a -> ReaderT r m a

MonadInterleave m => MonadInterleave (ReaderT r m)

Defined in Control.Monad.Random.Class

Methods

interleave :: ReaderT r m a -> ReaderT r m a

MonadRandom m => MonadRandom (ReaderT r m)

Defined in Control.Monad.Random.Class

Methods

getRandomR :: Random a => (a, a) -> ReaderT r m a

getRandom :: Random a => ReaderT r m a

getRandomRs :: Random a => (a, a) -> ReaderT r m [a]

getRandoms :: Random a => ReaderT r m [a]

MonadFail m => MonadFail (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

fail :: String -> ReaderT r m a

MonadFix m => MonadFix (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

mfix :: (a -> ReaderT r m a) -> ReaderT r m a

MonadIO m => MonadIO (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

liftIO :: IO a -> ReaderT r m a

MonadZip m => MonadZip (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

mzip :: ReaderT r m a -> ReaderT r m b -> ReaderT r m (a, b)

mzipWith :: (a -> b -> c) -> ReaderT r m a -> ReaderT r m b -> ReaderT r m c

munzip :: ReaderT r m (a, b) -> (ReaderT r m a, ReaderT r m b)

Contravariant m => Contravariant (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

contramap :: (a' -> a) -> ReaderT r m a -> ReaderT r m a'

(>$) :: b -> ReaderT r m b -> ReaderT r m a

Alternative m => Alternative (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

empty :: ReaderT r m a

(<|>) :: ReaderT r m a -> ReaderT r m a -> ReaderT r m a

some :: ReaderT r m a -> ReaderT r m [a]

many :: ReaderT r m a -> ReaderT r m [a]

Applicative m => Applicative (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

pure :: a -> ReaderT r m a

(<*>) :: ReaderT r m (a -> b) -> ReaderT r m a -> ReaderT r m b

liftA2 :: (a -> b -> c) -> ReaderT r m a -> ReaderT r m b -> ReaderT r m c

(*>) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m b

(<*) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m a

Functor m => Functor (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

fmap :: (a -> b) -> ReaderT r m a -> ReaderT r m b

(<$) :: a -> ReaderT r m b -> ReaderT r m a

Monad m => Monad (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

(>>=) :: ReaderT r m a -> (a -> ReaderT r m b) -> ReaderT r m b

(>>) :: ReaderT r m a -> ReaderT r m b -> ReaderT r m b

return :: a -> ReaderT r m a

MonadPlus m => MonadPlus (ReaderT r m)

Defined in Control.Monad.Trans.Reader

Methods

mzero :: ReaderT r m a

mplus :: ReaderT r m a -> ReaderT r m a -> ReaderT r m a

reader :: forall (m :: Type -> Type) r a. Monad m => (r -> a) -> ReaderT r m a

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

local

Arguments

:: forall r (m :: Type -> Type) a. (r -> r)

The function to modify the environment.

-> ReaderT r m a

Computation to run in the modified environment.

-> ReaderT r m a

Execute a computation in a modified environment (a specialization of withReaderT).

• runReaderT (local f m) = runReaderT m . f

asks

Arguments

:: forall (m :: Type -> Type) r a. Monad m

=> (r -> a)

The selector function to apply to the environment.

-> ReaderT r m a

Retrieve a function of the current environment.

• asks f = liftM f ask

ask :: forall (m :: Type -> Type) r. Monad m => ReaderT r m r

Fetch the value of the environment.

Reader MSF running and wrapping.

readerS :: Monad m => MSF m (r, a) b -> MSF (ReaderT r m) a b

Build an MSF in the Reader monad from one that takes the reader environment as an extra input. This is the opposite of runReaderS.

runReaderS :: Monad m => MSF (ReaderT r m) a b -> MSF m (r, a) b

Build an MSF that takes an environment as an extra input from one on the Reader monad. This is the opposite of readerS.

runReaderS_ :: Monad m => MSF (ReaderT s m) a b -> s -> MSF m a b

Build an MSF function that takes a fixed environment as additional input, from an MSF in the Reader monad.