Copyright	(c) Andy Gill 2001 (c) Oregon Graduate Institute of Science and Technology 2001 (c) Jeff Newbern 2003-2007 (c) Andriy Palamarchuk 2007
License	BSD-style (see the file LICENSE)
Maintainer	ross@soi.city.ac.uk
Stability	experimental
Portability	non-portable (type families)
Safe Haskell	None
Language	GHC2021

Control.Monad.Reader

Contents

MonadReader class
The Reader monad
The ReaderT monad transformer
Example 1: Simple Reader Usage
Example 2: Modifying Reader Content With local
Example 3: ReaderT Monad Transformer

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

class Monad m => MonadReader (m :: Type -> Type) where
- type EnvType (m :: Type -> Type)
- ask :: m (EnvType m)
- local :: (EnvType m -> EnvType m) -> m a -> m a
asks :: MonadReader m => (EnvType m -> a) -> m a
type Reader r = ReaderT r Identity
runReader :: Reader r a -> r -> a
mapReader :: (a -> b) -> Reader r a -> Reader r b
withReader :: (r' -> r) -> Reader r a -> Reader r' a
newtype ReaderT r (m :: Type -> Type) a = ReaderT {
- runReaderT :: 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
- (>>=) :: m a -> (a -> m b) -> m b
- (>>) :: m a -> m b -> m b
- return :: a -> m a
(=<<) :: Monad m => (a -> m b) -> m a -> m b
mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m ()
sequence_ :: (Foldable t, Monad m) => t (m a) -> m ()
class Functor (f :: Type -> Type) where
- fmap :: (a -> b) -> f a -> f b
- (<$) :: a -> f b -> f a
mapM :: (Traversable t, Monad m) => (a -> m b) -> t a -> m (t b)
sequence :: (Traversable t, Monad m) => t (m a) -> m (t a)
join :: Monad m => m (m a) -> m a
class (Alternative m, Monad m) => MonadPlus (m :: Type -> Type) where
- mzero :: m a
- mplus :: m a -> m a -> m a
class Monad m => MonadFail (m :: Type -> Type) where
- fail :: String -> m a
ap :: Monad m => m (a -> b) -> m a -> m b
liftM :: Monad m => (a1 -> r) -> m a1 -> m r
liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r
liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r
liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r
when :: Applicative f => Bool -> f () -> f ()
(<$!>) :: 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
filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a]
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 ()
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
replicateM :: Applicative m => Int -> m a -> m [a]
replicateM_ :: Applicative m => Int -> m a -> m ()
unless :: Applicative f => Bool -> f () -> f ()
zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c]
zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m ()
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)
guard :: Alternative f => Bool -> f ()
class Monad m => MonadFix (m :: Type -> Type) where
- mfix :: (a -> m a) -> m a
fix :: (a -> a) -> a
module Control.Monad.Trans

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

type Reader r = ReaderT r Identity #

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 runReaderT :: r -> m a

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-0.6.1.1-inplace" '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 #

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 #

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 #

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 type WriterType (ReaderT r m) = WriterType m

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-0.6.1.1-inplace" '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-0.6.1.1-inplace" '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 WriterType (ReaderT r m) = WriterType m

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-0.6.1.1-inplace" '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 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 NonEmpty
Instance details Defined in GHC.Internal.Base Methods (>>=) :: NonEmpty a -> (a -> NonEmpty b) -> NonEmpty b # (>>) :: NonEmpty a -> NonEmpty b -> NonEmpty b # return :: a -> NonEmpty a #
Monad Identity
Instance details Defined in GHC.Internal.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 GHC.Internal.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 GHC.Internal.Data.Monoid Methods (>>=) :: Last a -> (a -> Last b) -> Last b # (>>) :: Last a -> Last b -> Last b # return :: a -> Last a #
Monad Dual
Instance details Defined in GHC.Internal.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 GHC.Internal.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 GHC.Internal.Data.Semigroup.Internal Methods (>>=) :: Sum a -> (a -> Sum b) -> Sum b # (>>) :: Sum a -> Sum b -> Sum b # return :: a -> Sum a #
Monad Par1
Instance details Defined in GHC.Internal.Generics Methods (>>=) :: Par1 a -> (a -> Par1 b) -> Par1 b # (>>) :: Par1 a -> Par1 b -> Par1 b # return :: a -> Par1 a #
Monad IO
Instance details Defined in GHC.Internal.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.Internal.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.Internal.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.Internal.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 GHC.Internal.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 GHC.Internal.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 (U1 :: Type -> Type)
Instance details Defined in GHC.Internal.Generics Methods (>>=) :: U1 a -> (a -> U1 b) -> U1 b # (>>) :: U1 a -> U1 b -> U1 b # return :: a -> U1 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.Internal.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 GHC.Internal.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 GHC.Internal.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 GHC.Internal.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.Internal.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.Internal.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.Internal.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.Internal.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.Internal.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.Internal.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 #

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

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

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

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 Complex
Instance details Defined in Data.Complex Methods fmap :: (a -> b) -> Complex a -> Complex b # (<$) :: a -> Complex b -> Complex a #
Functor First
Instance details Defined in Data.Semigroup Methods fmap :: (a -> b) -> First a -> First b # (<$) :: 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 # (<$) :: a -> Min b -> Min a #
Functor ArgDescr
Instance details Defined in System.Console.GetOpt Methods fmap :: (a -> b) -> ArgDescr a -> ArgDescr b # (<$) :: 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 NonEmpty
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> NonEmpty a -> NonEmpty b # (<$) :: a -> NonEmpty b -> NonEmpty a #
Functor Identity
Instance details Defined in GHC.Internal.Data.Functor.Identity Methods fmap :: (a -> b) -> Identity a -> Identity b # (<$) :: a -> Identity b -> Identity a #
Functor First
Instance details Defined in GHC.Internal.Data.Monoid Methods fmap :: (a -> b) -> First a -> First b # (<$) :: a -> First b -> First a #
Functor Last
Instance details Defined in GHC.Internal.Data.Monoid Methods fmap :: (a -> b) -> Last a -> Last b # (<$) :: a -> Last b -> Last a #
Functor Dual
Instance details Defined in GHC.Internal.Data.Semigroup.Internal Methods fmap :: (a -> b) -> Dual a -> Dual b # (<$) :: a -> Dual b -> Dual a #
Functor Product
Instance details Defined in GHC.Internal.Data.Semigroup.Internal Methods fmap :: (a -> b) -> Product a -> Product b # (<$) :: a -> Product b -> Product a #
Functor Sum
Instance details Defined in GHC.Internal.Data.Semigroup.Internal Methods fmap :: (a -> b) -> Sum a -> Sum b # (<$) :: a -> Sum b -> Sum a #
Functor ZipList
Instance details Defined in GHC.Internal.Functor.ZipList Methods fmap :: (a -> b) -> ZipList a -> ZipList b # (<$) :: a -> ZipList b -> ZipList a #
Functor Par1
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> Par1 a -> Par1 b # (<$) :: a -> Par1 b -> Par1 a #
Functor IO
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> IO a -> IO b # (<$) :: a -> IO b -> IO a #
Functor Maybe
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> Maybe a -> Maybe b # (<$) :: a -> Maybe b -> Maybe a #
Functor Solo
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> Solo a -> Solo b # (<$) :: a -> Solo b -> Solo a #
Functor []
Instance details Defined in GHC.Internal.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 #
Functor (Arg a)
Instance details Defined in Data.Semigroup Methods fmap :: (a0 -> b) -> Arg a a0 -> Arg a b # (<$) :: a0 -> Arg a b -> Arg a a0 #
Arrow a => Functor (ArrowMonad a)
Instance details Defined in GHC.Internal.Control.Arrow Methods fmap :: (a0 -> b) -> ArrowMonad a a0 -> ArrowMonad a b # (<$) :: a0 -> ArrowMonad a b -> ArrowMonad a a0 #
Functor (Either a)
Instance details Defined in GHC.Internal.Data.Either Methods fmap :: (a0 -> b) -> Either a a0 -> Either a b # (<$) :: a0 -> Either a b -> Either a a0 #
Functor (U1 :: Type -> Type)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> U1 a -> U1 b # (<$) :: a -> U1 b -> U1 a #
Functor (V1 :: Type -> Type)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> V1 a -> V1 b # (<$) :: a -> V1 b -> V1 a #
Functor f => Functor (Lift f)
Instance details Defined in Control.Applicative.Lift Methods fmap :: (a -> b) -> Lift f a -> Lift f b # (<$) :: 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 # (<$) :: a -> MaybeT m b -> MaybeT m a #
Functor ((,) a)
Instance details Defined in GHC.Internal.Base Methods fmap :: (a0 -> b) -> (a, a0) -> (a, b) # (<$) :: 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 # (<$) :: a0 -> WrappedArrow a b b0 -> WrappedArrow a b a0 #
Functor m => Functor (Kleisli m a)
Instance details Defined in GHC.Internal.Control.Arrow Methods fmap :: (a0 -> b) -> Kleisli m a a0 -> Kleisli m a b # (<$) :: a0 -> Kleisli m a b -> Kleisli m a a0 #
Functor f => Functor (Ap f)
Instance details Defined in GHC.Internal.Data.Monoid Methods fmap :: (a -> b) -> Ap f a -> Ap f b # (<$) :: a -> Ap f b -> Ap f a #
Functor f => Functor (Alt f)
Instance details Defined in GHC.Internal.Data.Semigroup.Internal Methods fmap :: (a -> b) -> Alt f a -> Alt f b # (<$) :: a -> Alt f b -> Alt f a #
(Generic1 f, Functor (Rep1 f)) => Functor (Generically1 f)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> Generically1 f a -> Generically1 f b # (<$) :: a -> Generically1 f b -> Generically1 f a #
Functor f => Functor (Rec1 f)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> Rec1 f a -> Rec1 f b # (<$) :: a -> Rec1 f b -> Rec1 f a #
Functor (URec (Ptr ()) :: Type -> Type)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec (Ptr ()) a -> URec (Ptr ()) b # (<$) :: a -> URec (Ptr ()) b -> URec (Ptr ()) a #
Functor (URec Char :: Type -> Type)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec Char a -> URec Char b # (<$) :: a -> URec Char b -> URec Char a #
Functor (URec Double :: Type -> Type)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec Double a -> URec Double b # (<$) :: a -> URec Double b -> URec Double a #
Functor (URec Float :: Type -> Type)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec Float a -> URec Float b # (<$) :: a -> URec Float b -> URec Float a #
Functor (URec Int :: Type -> Type)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec Int a -> URec Int b # (<$) :: a -> URec Int b -> URec Int a #
Functor (URec Word :: Type -> Type)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> URec Word a -> URec Word b # (<$) :: 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 # (<$) :: a -> Reverse f b -> Reverse f a #
Functor ((,,) a b)
Instance details Defined in GHC.Internal.Base Methods fmap :: (a0 -> b0) -> (a, b, a0) -> (a, b, b0) # (<$) :: 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.Internal.Generics Methods fmap :: (a -> b) -> (f :: g) a -> (f :: g) b # (<$) :: a -> (f :: g) b -> (f :: g) a #
(Functor f, Functor g) => Functor (f :+: g)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> (f :+: g) a -> (f :+: g) b # (<$) :: a -> (f :+: g) b -> (f :+: g) a #
Functor (K1 i c :: Type -> Type)
Instance details Defined in GHC.Internal.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.Internal.Base Methods fmap :: (a0 -> b0) -> (a, b, c, a0) -> (a, b, c, b0) # (<$) :: a0 -> (a, b, c, b0) -> (a, b, c, a0) #
Functor ((->) r)
Instance details Defined in GHC.Internal.Base Methods fmap :: (a -> b) -> (r -> a) -> r -> b # (<$) :: 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 # (<$) :: a -> Compose f g b -> Compose f g a #
(Functor f, Functor g) => Functor (f :.: g)
Instance details Defined in GHC.Internal.Generics Methods fmap :: (a -> b) -> (f :.: g) a -> (f :.: g) b # (<$) :: a -> (f :.: g) b -> (f :.: g) a #
Functor f => Functor (M1 i c f)
Instance details Defined in GHC.Internal.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.Internal.Base Methods fmap :: (a0 -> b0) -> (a, b, c, d, a0) -> (a, b, c, d, b0) # (<$) :: a0 -> (a, b, c, d, b0) -> (a, b, c, d, a0) #
Functor ((,,,,,) a b c d e)
Instance details Defined in GHC.Internal.Base Methods fmap :: (a0 -> b0) -> (a, b, c, d, e, a0) -> (a, b, c, d, e, b0) # (<$) :: 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.Internal.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) #

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

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

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 IO
Instance details Defined in GHC.Internal.Base Methods mzero :: IO a # mplus :: IO a -> IO a -> IO a #
MonadPlus Maybe
Instance details Defined in GHC.Internal.Base Methods mzero :: Maybe a # mplus :: Maybe a -> Maybe a -> Maybe a #
MonadPlus []
Instance details Defined in GHC.Internal.Base Methods mzero :: [a] # mplus :: [a] -> [a] -> [a] #
(ArrowApply a, ArrowPlus a) => MonadPlus (ArrowMonad a)
Instance details Defined in GHC.Internal.Control.Arrow Methods mzero :: ArrowMonad a a0 # mplus :: ArrowMonad a a0 -> ArrowMonad a a0 -> ArrowMonad a a0 #
MonadPlus (U1 :: Type -> Type)
Instance details Defined in GHC.Internal.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 GHC.Internal.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 GHC.Internal.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 GHC.Internal.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.Internal.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.Internal.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.Internal.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 #

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

Methods

fail :: String -> m a #

Instances

Instances details

MonadFail IO
Instance details Defined in GHC.Internal.Control.Monad.Fail Methods fail :: String -> IO a #
MonadFail Maybe
Instance details Defined in GHC.Internal.Control.Monad.Fail Methods fail :: String -> Maybe a #
MonadFail []
Instance details Defined in GHC.Internal.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 GHC.Internal.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 #

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 () #

(<$!>) :: 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 #

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

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 () #

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 #

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

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

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

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

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

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) #

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 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 NonEmpty
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> NonEmpty a) -> NonEmpty a #
MonadFix Identity
Instance details Defined in GHC.Internal.Data.Functor.Identity Methods mfix :: (a -> Identity a) -> Identity a #
MonadFix First
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> First a) -> First a #
MonadFix Last
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Last a) -> Last a #
MonadFix Down
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Down a) -> Down a #
MonadFix Dual
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Dual a) -> Dual a #
MonadFix Product
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Product a) -> Product a #
MonadFix Sum
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Sum a) -> Sum a #
MonadFix Par1
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Par1 a) -> Par1 a #
MonadFix IO
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> IO a) -> IO a #
MonadFix Maybe
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Maybe a) -> Maybe a #
MonadFix Solo
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Solo a) -> Solo a #
MonadFix []
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> [a]) -> [a] #
MonadFix (Either e)
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Either e a) -> Either e a #
MonadFix (ST s)
Instance details Defined in GHC.Internal.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 GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Ap f a) -> Ap f a #
MonadFix f => MonadFix (Alt f)
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> Alt f a) -> Alt f a #
MonadFix f => MonadFix (Rec1 f)
Instance details Defined in GHC.Internal.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 GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> (f :: g) a) -> (f :: g) a #
MonadFix ((->) r)
Instance details Defined in GHC.Internal.Control.Monad.Fix Methods mfix :: (a -> r -> a) -> r -> a #
MonadFix f => MonadFix (M1 i c f)
Instance details Defined in GHC.Internal.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 #

module Control.Monad.Trans

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"

MonadReader class

Instances

The Reader monad

The ReaderT monad transformer

Instances

Instances

Instances

Instances

Instances

Instances

Example 1: Simple Reader Usage

Example 2: Modifying Reader Content With local

Example 3: ReaderT Monad Transformer

Example 2: Modifying Reader Content With `local`

Example 3: `ReaderT` Monad Transformer