monads-tf-0.3.0.1: Monad classes, using type families
Copyright(c) Andy Gill 2001
(c) Oregon Graduate Institute of Science and Technology 2001
(c) Jeff Newbern 2003-2007
(c) Andriy Palamarchuk 2007
LicenseBSD-style (see the file LICENSE)
Maintainerross@soi.city.ac.uk
Stabilityexperimental
Portabilitynon-portable (type families)
Safe HaskellNone
LanguageGHC2021

Control.Monad.Reader

Description

Computation type:
Computations which read values from a shared environment.
Binding strategy:
Monad values are functions from the environment to a value. The bound function is applied to the bound value, and both have access to the shared environment.
Useful for:
Maintaining variable bindings, or other shared environment.
Zero and plus:
None.
Example type:
Reader [(String,Value)] a

The Reader monad (also called the Environment monad). Represents a computation, which can read values from a shared environment, pass values from function to function, and execute sub-computations in a modified environment. Using Reader monad for such computations is often clearer and easier than using the State 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.

Synopsis

MonadReader class

class Monad m => MonadReader (m :: Type -> Type) where Source #

See examples in Control.Monad.Reader. Note, the partially applied function type (->) r is a simple reader monad. See the instance declaration below.

Associated Types

type EnvType (m :: Type -> Type) Source #

Methods

ask :: m (EnvType m) Source #

Retrieves the monad environment.

local Source #

Arguments

:: (EnvType m -> EnvType m)

The function to modify the environment.

-> m a

Reader to run in the modified environment.

-> m a 

Executes a computation in a modified environment.

Instances

Instances details
MonadReader m => MonadReader (MaybeT m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (MaybeT m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (MaybeT m) = EnvType m

Methods

ask :: MaybeT m (EnvType (MaybeT m)) Source #

local :: (EnvType (MaybeT m) -> EnvType (MaybeT m)) -> MaybeT m a -> MaybeT m a Source #

MonadReader m => MonadReader (ExceptT e m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (ExceptT e m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (ExceptT e m) = EnvType m

Methods

ask :: ExceptT e m (EnvType (ExceptT e m)) Source #

local :: (EnvType (ExceptT e m) -> EnvType (ExceptT e m)) -> ExceptT e m a -> ExceptT e m a Source #

MonadReader m => MonadReader (IdentityT m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (IdentityT m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (IdentityT m) = EnvType m

Methods

ask :: IdentityT m (EnvType (IdentityT m)) Source #

local :: (EnvType (IdentityT m) -> EnvType (IdentityT m)) -> IdentityT m a -> IdentityT m a Source #

Monad m => MonadReader (ReaderT r m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (ReaderT r m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (ReaderT r m) = r

Methods

ask :: ReaderT r m (EnvType (ReaderT r m)) Source #

local :: (EnvType (ReaderT r m) -> EnvType (ReaderT r m)) -> ReaderT r m a -> ReaderT r m a Source #

MonadReader m => MonadReader (StateT s m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (StateT s m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (StateT s m) = EnvType m

Methods

ask :: StateT s m (EnvType (StateT s m)) Source #

local :: (EnvType (StateT s m) -> EnvType (StateT s m)) -> StateT s m a -> StateT s m a Source #

MonadReader m => MonadReader (StateT s m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (StateT s m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (StateT s m) = EnvType m

Methods

ask :: StateT s m (EnvType (StateT s m)) Source #

local :: (EnvType (StateT s m) -> EnvType (StateT s m)) -> StateT s m a -> StateT s m a Source #

(Monoid w, MonadReader m) => MonadReader (WriterT w m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (WriterT w m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (WriterT w m) = EnvType m

Methods

ask :: WriterT w m (EnvType (WriterT w m)) Source #

local :: (EnvType (WriterT w m) -> EnvType (WriterT w m)) -> WriterT w m a -> WriterT w m a Source #

(Monoid w, MonadReader m) => MonadReader (WriterT w m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (WriterT w m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (WriterT w m) = EnvType m

Methods

ask :: WriterT w m (EnvType (WriterT w m)) Source #

local :: (EnvType (WriterT w m) -> EnvType (WriterT w m)) -> WriterT w m a -> WriterT w m a Source #

MonadReader m => MonadReader (ContT r m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (ContT r m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (ContT r m) = EnvType m

Methods

ask :: ContT r m (EnvType (ContT r m)) Source #

local :: (EnvType (ContT r m) -> EnvType (ContT r m)) -> ContT r m a -> ContT r m a Source #

MonadReader ((->) r) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType ((->) r) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType ((->) r) = r

Methods

ask :: r -> EnvType ((->) r) Source #

local :: (EnvType ((->) r) -> EnvType ((->) r)) -> (r -> a) -> r -> a Source #

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

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (RWST r w s m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (RWST r w s m) = r

Methods

ask :: RWST r w s m (EnvType (RWST r w s m)) Source #

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

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

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (RWST r w s m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (RWST r w s m) = r

Methods

ask :: RWST r w s m (EnvType (RWST r w s m)) Source #

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

asks Source #

Arguments

:: MonadReader m 
=> (EnvType m -> a)

The selector function to apply to the environment.

-> m a 

Retrieves a function of the current environment.

The Reader monad

runReader :: Reader r a -> r -> a #

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

withReader :: (r' -> r) -> Reader r a -> Reader r' a #

The ReaderT monad transformer

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

Constructors

ReaderT 

Fields

Instances

Instances details
Generic1 (ReaderT r m :: Type -> Type) 
Instance details

Defined in Control.Monad.Trans.Reader

Associated Types

type Rep1 (ReaderT r m :: Type -> Type) 
Instance details

Defined in Control.Monad.Trans.Reader

type Rep1 (ReaderT r m :: Type -> Type) = D1 ('MetaData "ReaderT" "Control.Monad.Trans.Reader" "transformers-0.6.1.0-a97a" 'True) (C1 ('MetaCons "ReaderT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runReaderT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) ((FUN 'Many r :: Type -> Type) :.: Rec1 m)))

Methods

from1 :: ReaderT r m a -> Rep1 (ReaderT r m) a

to1 :: Rep1 (ReaderT r m) a -> ReaderT r m a

MonadTrans (ReaderT r) 
Instance details

Defined in Control.Monad.Trans.Reader

Methods

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

MonadFail m => MonadFail (ReaderT r m) 
Instance details

Defined in Control.Monad.Trans.Reader

Methods

fail :: String -> ReaderT r m a #

MonadFix m => MonadFix (ReaderT r m) 
Instance details

Defined in Control.Monad.Trans.Reader

Methods

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

MonadIO m => MonadIO (ReaderT r m) 
Instance details

Defined in Control.Monad.Trans.Reader

Methods

liftIO :: IO a -> ReaderT r m a #

MonadZip m => MonadZip (ReaderT r m) 
Instance details

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) 
Instance details

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) 
Instance details

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) 
Instance details

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) 
Instance details

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) 
Instance details

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) 
Instance details

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 #

MonadCont m => MonadCont (ReaderT r m) Source # 
Instance details

Defined in Control.Monad.Cont.Class

Methods

callCC :: ((a -> ReaderT r m b) -> ReaderT r m a) -> ReaderT r m a Source #

MonadError m => MonadError (ReaderT r m) Source # 
Instance details

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (ReaderT r m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (ReaderT r m) = ErrorType m

Methods

throwError :: ErrorType (ReaderT r m) -> ReaderT r m a Source #

catchError :: ReaderT r m a -> (ErrorType (ReaderT r m) -> ReaderT r m a) -> ReaderT r m a Source #

Monad m => MonadReader (ReaderT r m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

Associated Types

type EnvType (ReaderT r m) 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (ReaderT r m) = r

Methods

ask :: ReaderT r m (EnvType (ReaderT r m)) Source #

local :: (EnvType (ReaderT r m) -> EnvType (ReaderT r m)) -> ReaderT r m a -> ReaderT r m a Source #

MonadState m => MonadState (ReaderT r m) Source # 
Instance details

Defined in Control.Monad.State.Class

Associated Types

type StateType (ReaderT r m) 
Instance details

Defined in Control.Monad.State.Class

type StateType (ReaderT r m) = StateType m

Methods

get :: ReaderT r m (StateType (ReaderT r m)) Source #

put :: StateType (ReaderT r m) -> ReaderT r m () Source #

MonadWriter m => MonadWriter (ReaderT r m) Source # 
Instance details

Defined in Control.Monad.Writer.Class

Associated Types

type WriterType (ReaderT r m) 
Instance details

Defined in Control.Monad.Writer.Class

Methods

tell :: WriterType (ReaderT r m) -> ReaderT r m () Source #

listen :: ReaderT r m a -> ReaderT r m (a, WriterType (ReaderT r m)) Source #

pass :: ReaderT r m (a, WriterType (ReaderT r m) -> WriterType (ReaderT r m)) -> ReaderT r m a Source #

Generic (ReaderT r m a) 
Instance details

Defined in Control.Monad.Trans.Reader

Associated Types

type Rep (ReaderT r m a) 
Instance details

Defined in Control.Monad.Trans.Reader

type Rep (ReaderT r m a) = D1 ('MetaData "ReaderT" "Control.Monad.Trans.Reader" "transformers-0.6.1.0-a97a" 'True) (C1 ('MetaCons "ReaderT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runReaderT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (r -> m a))))

Methods

from :: ReaderT r m a -> Rep (ReaderT r m a) x

to :: Rep (ReaderT r m a) x -> ReaderT r m a

type Rep1 (ReaderT r m :: Type -> Type) 
Instance details

Defined in Control.Monad.Trans.Reader

type Rep1 (ReaderT r m :: Type -> Type) = D1 ('MetaData "ReaderT" "Control.Monad.Trans.Reader" "transformers-0.6.1.0-a97a" 'True) (C1 ('MetaCons "ReaderT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runReaderT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) ((FUN 'Many r :: Type -> Type) :.: Rec1 m)))
type ErrorType (ReaderT r m) Source # 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (ReaderT r m) = ErrorType m
type EnvType (ReaderT r m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (ReaderT r m) = r
type StateType (ReaderT r m) Source # 
Instance details

Defined in Control.Monad.State.Class

type StateType (ReaderT r m) = StateType m
type WriterType (ReaderT r m) Source # 
Instance details

Defined in Control.Monad.Writer.Class

type Rep (ReaderT r m a) 
Instance details

Defined in Control.Monad.Trans.Reader

type Rep (ReaderT r m a) = D1 ('MetaData "ReaderT" "Control.Monad.Trans.Reader" "transformers-0.6.1.0-a97a" 'True) (C1 ('MetaCons "ReaderT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runReaderT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (r -> m a))))

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

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

class Applicative m => Monad (m :: Type -> Type) where #

Minimal complete definition

(>>=)

Methods

(>>=) :: m a -> (a -> m b) -> m b #

(>>) :: m a -> m b -> m b #

return :: a -> m a #

Instances

Instances details
Monad Complex 
Instance details

Defined in Data.Complex

Methods

(>>=) :: Complex a -> (a -> Complex b) -> Complex b #

(>>) :: Complex a -> Complex b -> Complex b #

return :: a -> Complex a #

Monad Identity 
Instance details

Defined in Data.Functor.Identity

Methods

(>>=) :: Identity a -> (a -> Identity b) -> Identity b #

(>>) :: Identity a -> Identity b -> Identity b #

return :: a -> Identity a #

Monad First 
Instance details

Defined in Data.Monoid

Methods

(>>=) :: First a -> (a -> First b) -> First b #

(>>) :: First a -> First b -> First b #

return :: a -> First a #

Monad Last 
Instance details

Defined in Data.Monoid

Methods

(>>=) :: Last a -> (a -> Last b) -> Last b #

(>>) :: Last a -> Last b -> Last b #

return :: a -> Last a #

Monad Down 
Instance details

Defined in Data.Ord

Methods

(>>=) :: Down a -> (a -> Down b) -> Down b #

(>>) :: Down a -> Down b -> Down b #

return :: a -> Down a #

Monad First 
Instance details

Defined in Data.Semigroup

Methods

(>>=) :: First a -> (a -> First b) -> First b #

(>>) :: First a -> First b -> First b #

return :: a -> First a #

Monad Last 
Instance details

Defined in Data.Semigroup

Methods

(>>=) :: Last a -> (a -> Last b) -> Last b #

(>>) :: Last a -> Last b -> Last b #

return :: a -> Last a #

Monad Max 
Instance details

Defined in Data.Semigroup

Methods

(>>=) :: Max a -> (a -> Max b) -> Max b #

(>>) :: Max a -> Max b -> Max b #

return :: a -> Max a #

Monad Min 
Instance details

Defined in Data.Semigroup

Methods

(>>=) :: Min a -> (a -> Min b) -> Min b #

(>>) :: Min a -> Min b -> Min b #

return :: a -> Min a #

Monad Dual 
Instance details

Defined in Data.Semigroup.Internal

Methods

(>>=) :: Dual a -> (a -> Dual b) -> Dual b #

(>>) :: Dual a -> Dual b -> Dual b #

return :: a -> Dual a #

Monad Product 
Instance details

Defined in Data.Semigroup.Internal

Methods

(>>=) :: Product a -> (a -> Product b) -> Product b #

(>>) :: Product a -> Product b -> Product b #

return :: a -> Product a #

Monad Sum 
Instance details

Defined in Data.Semigroup.Internal

Methods

(>>=) :: Sum a -> (a -> Sum b) -> Sum b #

(>>) :: Sum a -> Sum b -> Sum b #

return :: a -> Sum a #

Monad NonEmpty 
Instance details

Defined in GHC.Base

Methods

(>>=) :: NonEmpty a -> (a -> NonEmpty b) -> NonEmpty b #

(>>) :: NonEmpty a -> NonEmpty b -> NonEmpty b #

return :: a -> NonEmpty a #

Monad STM 
Instance details

Defined in GHC.Conc.Sync

Methods

(>>=) :: STM a -> (a -> STM b) -> STM b #

(>>) :: STM a -> STM b -> STM b #

return :: a -> STM a #

Monad NoIO 
Instance details

Defined in GHC.GHCi

Methods

(>>=) :: NoIO a -> (a -> NoIO b) -> NoIO b #

(>>) :: NoIO a -> NoIO b -> NoIO b #

return :: a -> NoIO a #

Monad Par1 
Instance details

Defined in GHC.Generics

Methods

(>>=) :: Par1 a -> (a -> Par1 b) -> Par1 b #

(>>) :: Par1 a -> Par1 b -> Par1 b #

return :: a -> Par1 a #

Monad P 
Instance details

Defined in Text.ParserCombinators.ReadP

Methods

(>>=) :: P a -> (a -> P b) -> P b #

(>>) :: P a -> P b -> P b #

return :: a -> P a #

Monad ReadP 
Instance details

Defined in Text.ParserCombinators.ReadP

Methods

(>>=) :: ReadP a -> (a -> ReadP b) -> ReadP b #

(>>) :: ReadP a -> ReadP b -> ReadP b #

return :: a -> ReadP a #

Monad ReadPrec 
Instance details

Defined in Text.ParserCombinators.ReadPrec

Methods

(>>=) :: ReadPrec a -> (a -> ReadPrec b) -> ReadPrec b #

(>>) :: ReadPrec a -> ReadPrec b -> ReadPrec b #

return :: a -> ReadPrec a #

Monad IO 
Instance details

Defined in GHC.Base

Methods

(>>=) :: IO a -> (a -> IO b) -> IO b #

(>>) :: IO a -> IO b -> IO b #

return :: a -> IO a #

Monad Maybe 
Instance details

Defined in GHC.Base

Methods

(>>=) :: Maybe a -> (a -> Maybe b) -> Maybe b #

(>>) :: Maybe a -> Maybe b -> Maybe b #

return :: a -> Maybe a #

Monad Solo 
Instance details

Defined in GHC.Base

Methods

(>>=) :: Solo a -> (a -> Solo b) -> Solo b #

(>>) :: Solo a -> Solo b -> Solo b #

return :: a -> Solo a #

Monad [] 
Instance details

Defined in GHC.Base

Methods

(>>=) :: [a] -> (a -> [b]) -> [b] #

(>>) :: [a] -> [b] -> [b] #

return :: a -> [a] #

Monad m => Monad (WrappedMonad m) 
Instance details

Defined in Control.Applicative

Methods

(>>=) :: WrappedMonad m a -> (a -> WrappedMonad m b) -> WrappedMonad m b #

(>>) :: WrappedMonad m a -> WrappedMonad m b -> WrappedMonad m b #

return :: a -> WrappedMonad m a #

ArrowApply a => Monad (ArrowMonad a) 
Instance details

Defined in Control.Arrow

Methods

(>>=) :: ArrowMonad a a0 -> (a0 -> ArrowMonad a b) -> ArrowMonad a b #

(>>) :: ArrowMonad a a0 -> ArrowMonad a b -> ArrowMonad a b #

return :: a0 -> ArrowMonad a a0 #

Monad (Either e) 
Instance details

Defined in Data.Either

Methods

(>>=) :: Either e a -> (a -> Either e b) -> Either e b #

(>>) :: Either e a -> Either e b -> Either e b #

return :: a -> Either e a #

Monad (Proxy :: Type -> Type) 
Instance details

Defined in Data.Proxy

Methods

(>>=) :: Proxy a -> (a -> Proxy b) -> Proxy b #

(>>) :: Proxy a -> Proxy b -> Proxy b #

return :: a -> Proxy a #

Monad (U1 :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

(>>=) :: U1 a -> (a -> U1 b) -> U1 b #

(>>) :: U1 a -> U1 b -> U1 b #

return :: a -> U1 a #

Monad (ST s) 
Instance details

Defined in GHC.ST

Methods

(>>=) :: ST s a -> (a -> ST s b) -> ST s b #

(>>) :: ST s a -> ST s b -> ST s b #

return :: a -> ST s a #

Monad m => Monad (MaybeT m) 
Instance details

Defined in Control.Monad.Trans.Maybe

Methods

(>>=) :: MaybeT m a -> (a -> MaybeT m b) -> MaybeT m b #

(>>) :: MaybeT m a -> MaybeT m b -> MaybeT m b #

return :: a -> MaybeT m a #

Monoid a => Monad ((,) a) 
Instance details

Defined in GHC.Base

Methods

(>>=) :: (a, a0) -> (a0 -> (a, b)) -> (a, b) #

(>>) :: (a, a0) -> (a, b) -> (a, b) #

return :: a0 -> (a, a0) #

Monad m => Monad (Kleisli m a) 
Instance details

Defined in Control.Arrow

Methods

(>>=) :: Kleisli m a a0 -> (a0 -> Kleisli m a b) -> Kleisli m a b #

(>>) :: Kleisli m a a0 -> Kleisli m a b -> Kleisli m a b #

return :: a0 -> Kleisli m a a0 #

Monad f => Monad (Ap f) 
Instance details

Defined in Data.Monoid

Methods

(>>=) :: Ap f a -> (a -> Ap f b) -> Ap f b #

(>>) :: Ap f a -> Ap f b -> Ap f b #

return :: a -> Ap f a #

Monad f => Monad (Alt f) 
Instance details

Defined in Data.Semigroup.Internal

Methods

(>>=) :: Alt f a -> (a -> Alt f b) -> Alt f b #

(>>) :: Alt f a -> Alt f b -> Alt f b #

return :: a -> Alt f a #

Monad f => Monad (Rec1 f) 
Instance details

Defined in GHC.Generics

Methods

(>>=) :: Rec1 f a -> (a -> Rec1 f b) -> Rec1 f b #

(>>) :: Rec1 f a -> Rec1 f b -> Rec1 f b #

return :: a -> Rec1 f a #

(Monoid w, Functor m, Monad m) => Monad (AccumT w m) 
Instance details

Defined in Control.Monad.Trans.Accum

Methods

(>>=) :: AccumT w m a -> (a -> AccumT w m b) -> AccumT w m b #

(>>) :: AccumT w m a -> AccumT w m b -> AccumT w m b #

return :: a -> AccumT w m a #

Monad m => Monad (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

(>>=) :: ExceptT e m a -> (a -> ExceptT e m b) -> ExceptT e m b #

(>>) :: ExceptT e m a -> ExceptT e m b -> ExceptT e m b #

return :: a -> ExceptT e m a #

Monad m => Monad (IdentityT m) 
Instance details

Defined in Control.Monad.Trans.Identity

Methods

(>>=) :: IdentityT m a -> (a -> IdentityT m b) -> IdentityT m b #

(>>) :: IdentityT m a -> IdentityT m b -> IdentityT m b #

return :: a -> IdentityT m a #

Monad m => Monad (ReaderT r m) 
Instance details

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 #

Monad m => Monad (SelectT r m) 
Instance details

Defined in Control.Monad.Trans.Select

Methods

(>>=) :: SelectT r m a -> (a -> SelectT r m b) -> SelectT r m b #

(>>) :: SelectT r m a -> SelectT r m b -> SelectT r m b #

return :: a -> SelectT r m a #

Monad m => Monad (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Lazy

Methods

(>>=) :: StateT s m a -> (a -> StateT s m b) -> StateT s m b #

(>>) :: StateT s m a -> StateT s m b -> StateT s m b #

return :: a -> StateT s m a #

Monad m => Monad (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Strict

Methods

(>>=) :: StateT s m a -> (a -> StateT s m b) -> StateT s m b #

(>>) :: StateT s m a -> StateT s m b -> StateT s m b #

return :: a -> StateT s m a #

Monad m => Monad (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.CPS

Methods

(>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b #

(>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b #

return :: a -> WriterT w m a #

(Monoid w, Monad m) => Monad (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.Lazy

Methods

(>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b #

(>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b #

return :: a -> WriterT w m a #

(Monoid w, Monad m) => Monad (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.Strict

Methods

(>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b #

(>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b #

return :: a -> WriterT w m a #

Monad m => Monad (Reverse m) 
Instance details

Defined in Data.Functor.Reverse

Methods

(>>=) :: Reverse m a -> (a -> Reverse m b) -> Reverse m b #

(>>) :: Reverse m a -> Reverse m b -> Reverse m b #

return :: a -> Reverse m a #

(Monoid a, Monoid b) => Monad ((,,) a b) 
Instance details

Defined in GHC.Base

Methods

(>>=) :: (a, b, a0) -> (a0 -> (a, b, b0)) -> (a, b, b0) #

(>>) :: (a, b, a0) -> (a, b, b0) -> (a, b, b0) #

return :: a0 -> (a, b, a0) #

(Monad f, Monad g) => Monad (Product f g) 
Instance details

Defined in Data.Functor.Product

Methods

(>>=) :: Product f g a -> (a -> Product f g b) -> Product f g b #

(>>) :: Product f g a -> Product f g b -> Product f g b #

return :: a -> Product f g a #

(Monad f, Monad g) => Monad (f :*: g) 
Instance details

Defined in GHC.Generics

Methods

(>>=) :: (f :*: g) a -> (a -> (f :*: g) b) -> (f :*: g) b #

(>>) :: (f :*: g) a -> (f :*: g) b -> (f :*: g) b #

return :: a -> (f :*: g) a #

Monad (ContT r m) 
Instance details

Defined in Control.Monad.Trans.Cont

Methods

(>>=) :: ContT r m a -> (a -> ContT r m b) -> ContT r m b #

(>>) :: ContT r m a -> ContT r m b -> ContT r m b #

return :: a -> ContT r m a #

(Monoid a, Monoid b, Monoid c) => Monad ((,,,) a b c) 
Instance details

Defined in GHC.Base

Methods

(>>=) :: (a, b, c, a0) -> (a0 -> (a, b, c, b0)) -> (a, b, c, b0) #

(>>) :: (a, b, c, a0) -> (a, b, c, b0) -> (a, b, c, b0) #

return :: a0 -> (a, b, c, a0) #

Monad ((->) r) 
Instance details

Defined in GHC.Base

Methods

(>>=) :: (r -> a) -> (a -> r -> b) -> r -> b #

(>>) :: (r -> a) -> (r -> b) -> r -> b #

return :: a -> r -> a #

Monad f => Monad (M1 i c f) 
Instance details

Defined in GHC.Generics

Methods

(>>=) :: M1 i c f a -> (a -> M1 i c f b) -> M1 i c f b #

(>>) :: M1 i c f a -> M1 i c f b -> M1 i c f b #

return :: a -> M1 i c f a #

Monad m => Monad (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.CPS

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 #

(Monoid w, Monad m) => Monad (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.Lazy

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 #

(Monoid w, Monad m) => Monad (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.Strict

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 #

class Monad m => MonadFail (m :: Type -> Type) where #

Methods

fail :: String -> m a #

Instances

Instances details
MonadFail P 
Instance details

Defined in Text.ParserCombinators.ReadP

Methods

fail :: String -> P a #

MonadFail ReadP 
Instance details

Defined in Text.ParserCombinators.ReadP

Methods

fail :: String -> ReadP a #

MonadFail ReadPrec 
Instance details

Defined in Text.ParserCombinators.ReadPrec

Methods

fail :: String -> ReadPrec a #

MonadFail IO 
Instance details

Defined in Control.Monad.Fail

Methods

fail :: String -> IO a #

MonadFail Maybe 
Instance details

Defined in Control.Monad.Fail

Methods

fail :: String -> Maybe a #

MonadFail [] 
Instance details

Defined in Control.Monad.Fail

Methods

fail :: String -> [a] #

Monad m => MonadFail (MaybeT m) 
Instance details

Defined in Control.Monad.Trans.Maybe

Methods

fail :: String -> MaybeT m a #

MonadFail f => MonadFail (Ap f) 
Instance details

Defined in Data.Monoid

Methods

fail :: String -> Ap f a #

(Monoid w, MonadFail m) => MonadFail (AccumT w m) 
Instance details

Defined in Control.Monad.Trans.Accum

Methods

fail :: String -> AccumT w m a #

MonadFail m => MonadFail (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

fail :: String -> ExceptT e m a #

MonadFail m => MonadFail (IdentityT m) 
Instance details

Defined in Control.Monad.Trans.Identity

Methods

fail :: String -> IdentityT m a #

MonadFail m => MonadFail (ReaderT r m) 
Instance details

Defined in Control.Monad.Trans.Reader

Methods

fail :: String -> ReaderT r m a #

MonadFail m => MonadFail (SelectT r m) 
Instance details

Defined in Control.Monad.Trans.Select

Methods

fail :: String -> SelectT r m a #

MonadFail m => MonadFail (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Lazy

Methods

fail :: String -> StateT s m a #

MonadFail m => MonadFail (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Strict

Methods

fail :: String -> StateT s m a #

MonadFail m => MonadFail (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.CPS

Methods

fail :: String -> WriterT w m a #

(Monoid w, MonadFail m) => MonadFail (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.Lazy

Methods

fail :: String -> WriterT w m a #

(Monoid w, MonadFail m) => MonadFail (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.Strict

Methods

fail :: String -> WriterT w m a #

MonadFail m => MonadFail (Reverse m) 
Instance details

Defined in Data.Functor.Reverse

Methods

fail :: String -> Reverse m a #

MonadFail m => MonadFail (ContT r m) 
Instance details

Defined in Control.Monad.Trans.Cont

Methods

fail :: String -> ContT r m a #

MonadFail m => MonadFail (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.CPS

Methods

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

(Monoid w, MonadFail m) => MonadFail (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

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

(Monoid w, MonadFail m) => MonadFail (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.Strict

Methods

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

mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m () #

sequence_ :: (Foldable t, Monad m) => t (m a) -> m () #

mapM :: (Traversable t, Monad m) => (a -> m b) -> t a -> m (t b) #

sequence :: (Traversable t, Monad m) => t (m a) -> m (t a) #

class Functor (f :: Type -> Type) where #

Minimal complete definition

fmap

Methods

fmap :: (a -> b) -> f a -> f b #

(<$) :: a -> f b -> f a #

Instances

Instances details
Functor ZipList 
Instance details

Defined in Control.Applicative

Methods

fmap :: (a -> b) -> ZipList a -> ZipList b #

(<$) :: a -> ZipList b -> ZipList a #

Functor Handler 
Instance details

Defined in Control.Exception

Methods

fmap :: (a -> b) -> Handler a -> Handler b #

(<$) :: a -> Handler b -> Handler a #

Functor Complex 
Instance details

Defined in Data.Complex

Methods

fmap :: (a -> b) -> Complex a -> Complex b #

(<$) :: a -> Complex b -> Complex a #

Functor Identity 
Instance details

Defined in Data.Functor.Identity

Methods

fmap :: (a -> b) -> Identity a -> Identity b #

(<$) :: a -> Identity b -> Identity a #

Functor First 
Instance details

Defined in Data.Monoid

Methods

fmap :: (a -> b) -> First a -> First b #

(<$) :: a -> First b -> First a #

Functor Last 
Instance details

Defined in Data.Monoid

Methods

fmap :: (a -> b) -> Last a -> Last b #

(<$) :: a -> Last b -> Last a #

Functor Down 
Instance details

Defined in Data.Ord

Methods

fmap :: (a -> b) -> Down a -> Down b #

(<$) :: a -> Down b -> Down a #

Functor First 
Instance details

Defined in Data.Semigroup

Methods

fmap :: (a -> b) -> First a -> First b #

(<$) :: a -> First b -> First a #

Functor Last 
Instance details

Defined in Data.Semigroup

Methods

fmap :: (a -> b) -> Last a -> Last b #

(<$) :: a -> Last b -> Last a #

Functor Max 
Instance details

Defined in Data.Semigroup

Methods

fmap :: (a -> b) -> Max a -> Max b #

(<$) :: a -> Max b -> Max a #

Functor Min 
Instance details

Defined in Data.Semigroup

Methods

fmap :: (a -> b) -> Min a -> Min b #

(<$) :: a -> Min b -> Min a #

Functor Dual 
Instance details

Defined in Data.Semigroup.Internal

Methods

fmap :: (a -> b) -> Dual a -> Dual b #

(<$) :: a -> Dual b -> Dual a #

Functor Product 
Instance details

Defined in Data.Semigroup.Internal

Methods

fmap :: (a -> b) -> Product a -> Product b #

(<$) :: a -> Product b -> Product a #

Functor Sum 
Instance details

Defined in Data.Semigroup.Internal

Methods

fmap :: (a -> b) -> Sum a -> Sum b #

(<$) :: a -> Sum b -> Sum a #

Functor NonEmpty 
Instance details

Defined in GHC.Base

Methods

fmap :: (a -> b) -> NonEmpty a -> NonEmpty b #

(<$) :: a -> NonEmpty b -> NonEmpty a #

Functor STM 
Instance details

Defined in GHC.Conc.Sync

Methods

fmap :: (a -> b) -> STM a -> STM b #

(<$) :: a -> STM b -> STM a #

Functor NoIO 
Instance details

Defined in GHC.GHCi

Methods

fmap :: (a -> b) -> NoIO a -> NoIO b #

(<$) :: a -> NoIO b -> NoIO a #

Functor Par1 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> Par1 a -> Par1 b #

(<$) :: a -> Par1 b -> Par1 a #

Functor ArgDescr 
Instance details

Defined in System.Console.GetOpt

Methods

fmap :: (a -> b) -> ArgDescr a -> ArgDescr b #

(<$) :: a -> ArgDescr b -> ArgDescr a #

Functor ArgOrder 
Instance details

Defined in System.Console.GetOpt

Methods

fmap :: (a -> b) -> ArgOrder a -> ArgOrder b #

(<$) :: a -> ArgOrder b -> ArgOrder a #

Functor OptDescr 
Instance details

Defined in System.Console.GetOpt

Methods

fmap :: (a -> b) -> OptDescr a -> OptDescr b #

(<$) :: a -> OptDescr b -> OptDescr a #

Functor P 
Instance details

Defined in Text.ParserCombinators.ReadP

Methods

fmap :: (a -> b) -> P a -> P b #

(<$) :: a -> P b -> P a #

Functor ReadP 
Instance details

Defined in Text.ParserCombinators.ReadP

Methods

fmap :: (a -> b) -> ReadP a -> ReadP b #

(<$) :: a -> ReadP b -> ReadP a #

Functor ReadPrec 
Instance details

Defined in Text.ParserCombinators.ReadPrec

Methods

fmap :: (a -> b) -> ReadPrec a -> ReadPrec b #

(<$) :: a -> ReadPrec b -> ReadPrec a #

Functor IO 
Instance details

Defined in GHC.Base

Methods

fmap :: (a -> b) -> IO a -> IO b #

(<$) :: a -> IO b -> IO a #

Functor Maybe 
Instance details

Defined in GHC.Base

Methods

fmap :: (a -> b) -> Maybe a -> Maybe b #

(<$) :: a -> Maybe b -> Maybe a #

Functor Solo 
Instance details

Defined in GHC.Base

Methods

fmap :: (a -> b) -> Solo a -> Solo b #

(<$) :: a -> Solo b -> Solo a #

Functor [] 
Instance details

Defined in GHC.Base

Methods

fmap :: (a -> b) -> [a] -> [b] #

(<$) :: a -> [b] -> [a] #

Monad m => Functor (WrappedMonad m) 
Instance details

Defined in Control.Applicative

Methods

fmap :: (a -> b) -> WrappedMonad m a -> WrappedMonad m b #

(<$) :: a -> WrappedMonad m b -> WrappedMonad m a #

Arrow a => Functor (ArrowMonad a) 
Instance details

Defined in Control.Arrow

Methods

fmap :: (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b #

(<$) :: a0 -> ArrowMonad a b -> ArrowMonad a a0 #

Functor (Either a) 
Instance details

Defined in Data.Either

Methods

fmap :: (a0 -> b) -> Either a a0 -> Either a b #

(<$) :: a0 -> Either a b -> Either a a0 #

Functor (Proxy :: Type -> Type) 
Instance details

Defined in Data.Proxy

Methods

fmap :: (a -> b) -> Proxy a -> Proxy b #

(<$) :: a -> Proxy b -> Proxy a #

Functor (Arg a) 
Instance details

Defined in Data.Semigroup

Methods

fmap :: (a0 -> b) -> Arg a a0 -> Arg a b #

(<$) :: a0 -> Arg a b -> Arg a a0 #

Functor (Array i) 
Instance details

Defined in GHC.Arr

Methods

fmap :: (a -> b) -> Array i a -> Array i b #

(<$) :: a -> Array i b -> Array i a #

Functor (U1 :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> U1 a -> U1 b #

(<$) :: a -> U1 b -> U1 a #

Functor (V1 :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> V1 a -> V1 b #

(<$) :: a -> V1 b -> V1 a #

Functor (ST s) 
Instance details

Defined in GHC.ST

Methods

fmap :: (a -> b) -> ST s a -> ST s b #

(<$) :: a -> ST s b -> ST s a #

Functor f => Functor (Lift f) 
Instance details

Defined in Control.Applicative.Lift

Methods

fmap :: (a -> b) -> Lift f a -> Lift f b #

(<$) :: a -> Lift f b -> Lift f a #

Functor m => Functor (MaybeT m) 
Instance details

Defined in Control.Monad.Trans.Maybe

Methods

fmap :: (a -> b) -> MaybeT m a -> MaybeT m b #

(<$) :: a -> MaybeT m b -> MaybeT m a #

Functor ((,) a) 
Instance details

Defined in GHC.Base

Methods

fmap :: (a0 -> b) -> (a, a0) -> (a, b) #

(<$) :: a0 -> (a, b) -> (a, a0) #

Arrow a => Functor (WrappedArrow a b) 
Instance details

Defined in Control.Applicative

Methods

fmap :: (a0 -> b0) -> WrappedArrow a b a0 -> WrappedArrow a b b0 #

(<$) :: a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 #

Functor m => Functor (Kleisli m a) 
Instance details

Defined in Control.Arrow

Methods

fmap :: (a0 -> b) -> Kleisli m a a0 -> Kleisli m a b #

(<$) :: a0 -> Kleisli m a b -> Kleisli m a a0 #

Functor (Const m :: Type -> Type) 
Instance details

Defined in Data.Functor.Const

Methods

fmap :: (a -> b) -> Const m a -> Const m b #

(<$) :: a -> Const m b -> Const m a #

Functor f => Functor (Ap f) 
Instance details

Defined in Data.Monoid

Methods

fmap :: (a -> b) -> Ap f a -> Ap f b #

(<$) :: a -> Ap f b -> Ap f a #

Functor f => Functor (Alt f) 
Instance details

Defined in Data.Semigroup.Internal

Methods

fmap :: (a -> b) -> Alt f a -> Alt f b #

(<$) :: a -> Alt f b -> Alt f a #

(Generic1 f, Functor (Rep1 f)) => Functor (Generically1 f) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> Generically1 f a -> Generically1 f b #

(<$) :: a -> Generically1 f b -> Generically1 f a #

Functor f => Functor (Rec1 f) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> Rec1 f a -> Rec1 f b #

(<$) :: a -> Rec1 f b -> Rec1 f a #

Functor (URec (Ptr ()) :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec (Ptr ()) a -> URec (Ptr ()) b #

(<$) :: a -> URec (Ptr ()) b -> URec (Ptr ()) a #

Functor (URec Char :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec Char a -> URec Char b #

(<$) :: a -> URec Char b -> URec Char a #

Functor (URec Double :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec Double a -> URec Double b #

(<$) :: a -> URec Double b -> URec Double a #

Functor (URec Float :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec Float a -> URec Float b #

(<$) :: a -> URec Float b -> URec Float a #

Functor (URec Int :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec Int a -> URec Int b #

(<$) :: a -> URec Int b -> URec Int a #

Functor (URec Word :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> URec Word a -> URec Word b #

(<$) :: a -> URec Word b -> URec Word a #

Functor f => Functor (Backwards f) 
Instance details

Defined in Control.Applicative.Backwards

Methods

fmap :: (a -> b) -> Backwards f a -> Backwards f b #

(<$) :: a -> Backwards f b -> Backwards f a #

Functor m => Functor (AccumT w m) 
Instance details

Defined in Control.Monad.Trans.Accum

Methods

fmap :: (a -> b) -> AccumT w m a -> AccumT w m b #

(<$) :: a -> AccumT w m b -> AccumT w m a #

Functor m => Functor (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

fmap :: (a -> b) -> ExceptT e m a -> ExceptT e m b #

(<$) :: a -> ExceptT e m b -> ExceptT e m a #

Functor m => Functor (IdentityT m) 
Instance details

Defined in Control.Monad.Trans.Identity

Methods

fmap :: (a -> b) -> IdentityT m a -> IdentityT m b #

(<$) :: a -> IdentityT m b -> IdentityT m a #

Functor m => Functor (ReaderT r m) 
Instance details

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 #

Functor m => Functor (SelectT r m) 
Instance details

Defined in Control.Monad.Trans.Select

Methods

fmap :: (a -> b) -> SelectT r m a -> SelectT r m b #

(<$) :: a -> SelectT r m b -> SelectT r m a #

Functor m => Functor (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Lazy

Methods

fmap :: (a -> b) -> StateT s m a -> StateT s m b #

(<$) :: a -> StateT s m b -> StateT s m a #

Functor m => Functor (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Strict

Methods

fmap :: (a -> b) -> StateT s m a -> StateT s m b #

(<$) :: a -> StateT s m b -> StateT s m a #

Functor m => Functor (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.CPS

Methods

fmap :: (a -> b) -> WriterT w m a -> WriterT w m b #

(<$) :: a -> WriterT w m b -> WriterT w m a #

Functor m => Functor (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.Lazy

Methods

fmap :: (a -> b) -> WriterT w m a -> WriterT w m b #

(<$) :: a -> WriterT w m b -> WriterT w m a #

Functor m => Functor (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.Strict

Methods

fmap :: (a -> b) -> WriterT w m a -> WriterT w m b #

(<$) :: a -> WriterT w m b -> WriterT w m a #

Functor (Constant a :: Type -> Type) 
Instance details

Defined in Data.Functor.Constant

Methods

fmap :: (a0 -> b) -> Constant a a0 -> Constant a b #

(<$) :: a0 -> Constant a b -> Constant a a0 #

Functor f => Functor (Reverse f) 
Instance details

Defined in Data.Functor.Reverse

Methods

fmap :: (a -> b) -> Reverse f a -> Reverse f b #

(<$) :: a -> Reverse f b -> Reverse f a #

Functor ((,,) a b) 
Instance details

Defined in GHC.Base

Methods

fmap :: (a0 -> b0) -> (a, b, a0) -> (a, b, b0) #

(<$) :: a0 -> (a, b, b0) -> (a, b, a0) #

(Functor f, Functor g) => Functor (Product f g) 
Instance details

Defined in Data.Functor.Product

Methods

fmap :: (a -> b) -> Product f g a -> Product f g b #

(<$) :: a -> Product f g b -> Product f g a #

(Functor f, Functor g) => Functor (Sum f g) 
Instance details

Defined in Data.Functor.Sum

Methods

fmap :: (a -> b) -> Sum f g a -> Sum f g b #

(<$) :: a -> Sum f g b -> Sum f g a #

(Functor f, Functor g) => Functor (f :*: g) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> (f :*: g) a -> (f :*: g) b #

(<$) :: a -> (f :*: g) b -> (f :*: g) a #

(Functor f, Functor g) => Functor (f :+: g) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> (f :+: g) a -> (f :+: g) b #

(<$) :: a -> (f :+: g) b -> (f :+: g) a #

Functor (K1 i c :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> K1 i c a -> K1 i c b #

(<$) :: a -> K1 i c b -> K1 i c a #

Functor (ContT r m) 
Instance details

Defined in Control.Monad.Trans.Cont

Methods

fmap :: (a -> b) -> ContT r m a -> ContT r m b #

(<$) :: a -> ContT r m b -> ContT r m a #

Functor ((,,,) a b c) 
Instance details

Defined in GHC.Base

Methods

fmap :: (a0 -> b0) -> (a, b, c, a0) -> (a, b, c, b0) #

(<$) :: a0 -> (a, b, c, b0) -> (a, b, c, a0) #

Functor ((->) r) 
Instance details

Defined in GHC.Base

Methods

fmap :: (a -> b) -> (r -> a) -> r -> b #

(<$) :: a -> (r -> b) -> r -> a #

(Functor f, Functor g) => Functor (Compose f g) 
Instance details

Defined in Data.Functor.Compose

Methods

fmap :: (a -> b) -> Compose f g a -> Compose f g b #

(<$) :: a -> Compose f g b -> Compose f g a #

(Functor f, Functor g) => Functor (f :.: g) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> (f :.: g) a -> (f :.: g) b #

(<$) :: a -> (f :.: g) b -> (f :.: g) a #

Functor f => Functor (M1 i c f) 
Instance details

Defined in GHC.Generics

Methods

fmap :: (a -> b) -> M1 i c f a -> M1 i c f b #

(<$) :: a -> M1 i c f b -> M1 i c f a #

Functor m => Functor (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.CPS

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 #

Functor m => Functor (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.Lazy

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 #

Functor m => Functor (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.Strict

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 #

Functor ((,,,,) a b c d) 
Instance details

Defined in GHC.Base

Methods

fmap :: (a0 -> b0) -> (a, b, c, d, a0) -> (a, b, c, d, b0) #

(<$) :: a0 -> (a, b, c, d, b0) -> (a, b, c, d, a0) #

Functor ((,,,,,) a b c d e) 
Instance details

Defined in GHC.Base

Methods

fmap :: (a0 -> b0) -> (a, b, c, d, e, a0) -> (a, b, c, d, e, b0) #

(<$) :: a0 -> (a, b, c, d, e, b0) -> (a, b, c, d, e, a0) #

Functor ((,,,,,,) a b c d e f) 
Instance details

Defined in GHC.Base

Methods

fmap :: (a0 -> b0) -> (a, b, c, d, e, f, a0) -> (a, b, c, d, e, f, b0) #

(<$) :: a0 -> (a, b, c, d, e, f, b0) -> (a, b, c, d, e, f, a0) #

(=<<) :: Monad m => (a -> m b) -> m a -> m b #

join :: Monad m => m (m a) -> m a #

class (Alternative m, Monad m) => MonadPlus (m :: Type -> Type) where #

Minimal complete definition

Nothing

Methods

mzero :: m a #

mplus :: m a -> m a -> m a #

Instances

Instances details
MonadPlus STM 
Instance details

Defined in GHC.Conc.Sync

Methods

mzero :: STM a #

mplus :: STM a -> STM a -> STM a #

MonadPlus P 
Instance details

Defined in Text.ParserCombinators.ReadP

Methods

mzero :: P a #

mplus :: P a -> P a -> P a #

MonadPlus ReadP 
Instance details

Defined in Text.ParserCombinators.ReadP

Methods

mzero :: ReadP a #

mplus :: ReadP a -> ReadP a -> ReadP a #

MonadPlus ReadPrec 
Instance details

Defined in Text.ParserCombinators.ReadPrec

Methods

mzero :: ReadPrec a #

mplus :: ReadPrec a -> ReadPrec a -> ReadPrec a #

MonadPlus IO 
Instance details

Defined in GHC.Base

Methods

mzero :: IO a #

mplus :: IO a -> IO a -> IO a #

MonadPlus Maybe 
Instance details

Defined in GHC.Base

Methods

mzero :: Maybe a #

mplus :: Maybe a -> Maybe a -> Maybe a #

MonadPlus [] 
Instance details

Defined in GHC.Base

Methods

mzero :: [a] #

mplus :: [a] -> [a] -> [a] #

(ArrowApply a, ArrowPlus a) => MonadPlus (ArrowMonad a) 
Instance details

Defined in Control.Arrow

Methods

mzero :: ArrowMonad a a0 #

mplus :: ArrowMonad a a0 -> ArrowMonad a a0 -> ArrowMonad a a0 #

MonadPlus (Proxy :: Type -> Type) 
Instance details

Defined in Data.Proxy

Methods

mzero :: Proxy a #

mplus :: Proxy a -> Proxy a -> Proxy a #

MonadPlus (U1 :: Type -> Type) 
Instance details

Defined in GHC.Generics

Methods

mzero :: U1 a #

mplus :: U1 a -> U1 a -> U1 a #

Monad m => MonadPlus (MaybeT m) 
Instance details

Defined in Control.Monad.Trans.Maybe

Methods

mzero :: MaybeT m a #

mplus :: MaybeT m a -> MaybeT m a -> MaybeT m a #

MonadPlus m => MonadPlus (Kleisli m a) 
Instance details

Defined in Control.Arrow

Methods

mzero :: Kleisli m a a0 #

mplus :: Kleisli m a a0 -> Kleisli m a a0 -> Kleisli m a a0 #

MonadPlus f => MonadPlus (Ap f) 
Instance details

Defined in Data.Monoid

Methods

mzero :: Ap f a #

mplus :: Ap f a -> Ap f a -> Ap f a #

MonadPlus f => MonadPlus (Alt f) 
Instance details

Defined in Data.Semigroup.Internal

Methods

mzero :: Alt f a #

mplus :: Alt f a -> Alt f a -> Alt f a #

MonadPlus f => MonadPlus (Rec1 f) 
Instance details

Defined in GHC.Generics

Methods

mzero :: Rec1 f a #

mplus :: Rec1 f a -> Rec1 f a -> Rec1 f a #

(Monoid w, Functor m, MonadPlus m) => MonadPlus (AccumT w m) 
Instance details

Defined in Control.Monad.Trans.Accum

Methods

mzero :: AccumT w m a #

mplus :: AccumT w m a -> AccumT w m a -> AccumT w m a #

(Monad m, Monoid e) => MonadPlus (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

mzero :: ExceptT e m a #

mplus :: ExceptT e m a -> ExceptT e m a -> ExceptT e m a #

MonadPlus m => MonadPlus (IdentityT m) 
Instance details

Defined in Control.Monad.Trans.Identity

Methods

mzero :: IdentityT m a #

mplus :: IdentityT m a -> IdentityT m a -> IdentityT m a #

MonadPlus m => MonadPlus (ReaderT r m) 
Instance details

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 #

MonadPlus m => MonadPlus (SelectT r m) 
Instance details

Defined in Control.Monad.Trans.Select

Methods

mzero :: SelectT r m a #

mplus :: SelectT r m a -> SelectT r m a -> SelectT r m a #

MonadPlus m => MonadPlus (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Lazy

Methods

mzero :: StateT s m a #

mplus :: StateT s m a -> StateT s m a -> StateT s m a #

MonadPlus m => MonadPlus (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Strict

Methods

mzero :: StateT s m a #

mplus :: StateT s m a -> StateT s m a -> StateT s m a #

(Functor m, MonadPlus m) => MonadPlus (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.CPS

Methods

mzero :: WriterT w m a #

mplus :: WriterT w m a -> WriterT w m a -> WriterT w m a #

(Monoid w, MonadPlus m) => MonadPlus (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.Lazy

Methods

mzero :: WriterT w m a #

mplus :: WriterT w m a -> WriterT w m a -> WriterT w m a #

(Monoid w, MonadPlus m) => MonadPlus (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.Strict

Methods

mzero :: WriterT w m a #

mplus :: WriterT w m a -> WriterT w m a -> WriterT w m a #

MonadPlus m => MonadPlus (Reverse m) 
Instance details

Defined in Data.Functor.Reverse

Methods

mzero :: Reverse m a #

mplus :: Reverse m a -> Reverse m a -> Reverse m a #

(MonadPlus f, MonadPlus g) => MonadPlus (Product f g) 
Instance details

Defined in Data.Functor.Product

Methods

mzero :: Product f g a #

mplus :: Product f g a -> Product f g a -> Product f g a #

(MonadPlus f, MonadPlus g) => MonadPlus (f :*: g) 
Instance details

Defined in GHC.Generics

Methods

mzero :: (f :*: g) a #

mplus :: (f :*: g) a -> (f :*: g) a -> (f :*: g) a #

MonadPlus f => MonadPlus (M1 i c f) 
Instance details

Defined in GHC.Generics

Methods

mzero :: M1 i c f a #

mplus :: M1 i c f a -> M1 i c f a -> M1 i c f a #

(Functor m, MonadPlus m) => MonadPlus (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.CPS

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 #

(Monoid w, MonadPlus m) => MonadPlus (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.Lazy

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 #

(Monoid w, MonadPlus m) => MonadPlus (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.Strict

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 #

ap :: Monad m => m (a -> b) -> m a -> m b #

liftM :: Monad m => (a1 -> r) -> m a1 -> m r #

liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r #

liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r #

liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r #

liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r #

when :: Applicative f => Bool -> f () -> f () #

forM_ :: (Foldable t, Monad m) => t a -> (a -> m b) -> m () #

msum :: (Foldable t, MonadPlus m) => t (m a) -> m a #

void :: Functor f => f a -> f () #

forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b) #

(<$!>) :: Monad m => (a -> b) -> m a -> m b #

(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c #

(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c #

foldM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b #

foldM_ :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m () #

replicateM :: Applicative m => Int -> m a -> m [a] #

replicateM_ :: Applicative m => Int -> m a -> m () #

unless :: Applicative f => Bool -> f () -> f () #

filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a] #

forever :: Applicative f => f a -> f b #

mapAndUnzipM :: Applicative m => (a -> m (b, c)) -> [a] -> m ([b], [c]) #

mfilter :: MonadPlus m => (a -> Bool) -> m a -> m a #

zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c] #

zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m () #

guard :: Alternative f => Bool -> f () #

class Monad m => MonadFix (m :: Type -> Type) where #

Methods

mfix :: (a -> m a) -> m a #

Instances

Instances details
MonadFix Complex 
Instance details

Defined in Data.Complex

Methods

mfix :: (a -> Complex a) -> Complex a #

MonadFix Identity 
Instance details

Defined in Data.Functor.Identity

Methods

mfix :: (a -> Identity a) -> Identity a #

MonadFix First 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> First a) -> First a #

MonadFix Last 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Last a) -> Last a #

MonadFix Down 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Down a) -> Down a #

MonadFix First 
Instance details

Defined in Data.Semigroup

Methods

mfix :: (a -> First a) -> First a #

MonadFix Last 
Instance details

Defined in Data.Semigroup

Methods

mfix :: (a -> Last a) -> Last a #

MonadFix Max 
Instance details

Defined in Data.Semigroup

Methods

mfix :: (a -> Max a) -> Max a #

MonadFix Min 
Instance details

Defined in Data.Semigroup

Methods

mfix :: (a -> Min a) -> Min a #

MonadFix Dual 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Dual a) -> Dual a #

MonadFix Product 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Product a) -> Product a #

MonadFix Sum 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Sum a) -> Sum a #

MonadFix NonEmpty 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> NonEmpty a) -> NonEmpty a #

MonadFix Par1 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Par1 a) -> Par1 a #

MonadFix IO 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> IO a) -> IO a #

MonadFix Maybe 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Maybe a) -> Maybe a #

MonadFix Solo 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Solo a) -> Solo a #

MonadFix [] 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> [a]) -> [a] #

MonadFix (Either e) 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Either e a) -> Either e a #

MonadFix (ST s) 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> ST s a) -> ST s a #

MonadFix m => MonadFix (MaybeT m) 
Instance details

Defined in Control.Monad.Trans.Maybe

Methods

mfix :: (a -> MaybeT m a) -> MaybeT m a #

MonadFix f => MonadFix (Ap f) 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Ap f a) -> Ap f a #

MonadFix f => MonadFix (Alt f) 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Alt f a) -> Alt f a #

MonadFix f => MonadFix (Rec1 f) 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> Rec1 f a) -> Rec1 f a #

(Monoid w, Functor m, MonadFix m) => MonadFix (AccumT w m) 
Instance details

Defined in Control.Monad.Trans.Accum

Methods

mfix :: (a -> AccumT w m a) -> AccumT w m a #

MonadFix m => MonadFix (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

mfix :: (a -> ExceptT e m a) -> ExceptT e m a #

MonadFix m => MonadFix (IdentityT m) 
Instance details

Defined in Control.Monad.Trans.Identity

Methods

mfix :: (a -> IdentityT m a) -> IdentityT m a #

MonadFix m => MonadFix (ReaderT r m) 
Instance details

Defined in Control.Monad.Trans.Reader

Methods

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

MonadFix m => MonadFix (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Lazy

Methods

mfix :: (a -> StateT s m a) -> StateT s m a #

MonadFix m => MonadFix (StateT s m) 
Instance details

Defined in Control.Monad.Trans.State.Strict

Methods

mfix :: (a -> StateT s m a) -> StateT s m a #

MonadFix m => MonadFix (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.CPS

Methods

mfix :: (a -> WriterT w m a) -> WriterT w m a #

(Monoid w, MonadFix m) => MonadFix (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.Lazy

Methods

mfix :: (a -> WriterT w m a) -> WriterT w m a #

(Monoid w, MonadFix m) => MonadFix (WriterT w m) 
Instance details

Defined in Control.Monad.Trans.Writer.Strict

Methods

mfix :: (a -> WriterT w m a) -> WriterT w m a #

(MonadFix f, MonadFix g) => MonadFix (Product f g) 
Instance details

Defined in Data.Functor.Product

Methods

mfix :: (a -> Product f g a) -> Product f g a #

(MonadFix f, MonadFix g) => MonadFix (f :*: g) 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> (f :*: g) a) -> (f :*: g) a #

MonadFix ((->) r) 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> r -> a) -> r -> a #

MonadFix f => MonadFix (M1 i c f) 
Instance details

Defined in Control.Monad.Fix

Methods

mfix :: (a -> M1 i c f a) -> M1 i c f a #

MonadFix m => MonadFix (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.CPS

Methods

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

(Monoid w, MonadFix m) => MonadFix (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.Lazy

Methods

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

(Monoid w, MonadFix m) => MonadFix (RWST r w s m) 
Instance details

Defined in Control.Monad.Trans.RWS.Strict

Methods

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

fix :: (a -> a) -> a #

Example 1: Simple Reader Usage

In this example the Reader monad provides access to variable bindings. Bindings are a Map of integer variables. The variable count contains number of variables in the bindings. You can see how to run a Reader monad and retrieve data from it with runReader, how to access the Reader data with ask and asks.

 type Bindings = Map String Int;

-- Returns True if the "count" variable contains correct bindings size.
isCountCorrect :: Bindings -> Bool
isCountCorrect bindings = runReader calc_isCountCorrect bindings

-- The Reader monad, which implements this complicated check.
calc_isCountCorrect :: Reader Bindings Bool
calc_isCountCorrect = do
    count <- asks (lookupVar "count")
    bindings <- ask
    return (count == (Map.size bindings))

-- The selector function to  use with 'asks'.
-- Returns value of the variable with specified name.
lookupVar :: String -> Bindings -> Int
lookupVar name bindings = fromJust (Map.lookup name bindings)

sampleBindings = Map.fromList [("count",3), ("1",1), ("b",2)]

main = do
    putStr $ "Count is correct for bindings " ++ (show sampleBindings) ++ ": ";
    putStrLn $ show (isCountCorrect sampleBindings);

Example 2: Modifying Reader Content With local

Shows how to modify Reader content with local.

calculateContentLen :: Reader String Int
calculateContentLen = do
    content <- ask
    return (length content);

-- Calls calculateContentLen after adding a prefix to the Reader content.
calculateModifiedContentLen :: Reader String Int
calculateModifiedContentLen = local ("Prefix " ++) calculateContentLen

main = do
    let s = "12345";
    let modifiedLen = runReader calculateModifiedContentLen s
    let len = runReader calculateContentLen s
    putStrLn $ "Modified 's' length: " ++ (show modifiedLen)
    putStrLn $ "Original 's' length: " ++ (show len)

Example 3: ReaderT Monad Transformer

Now you are thinking: 'Wow, what a great monad! I wish I could use Reader functionality in MyFavoriteComplexMonad!'. Don't worry. This can be easy done with the ReaderT monad transformer. This example shows how to combine ReaderT with the IO monad.

-- The Reader/IO combined monad, where Reader stores a string.
printReaderContent :: ReaderT String IO ()
printReaderContent = do
    content <- ask
    liftIO $ putStrLn ("The Reader Content: " ++ content)

main = do
    runReaderT printReaderContent "Some Content"