monads-tf-0.3.0.1: Monad classes, using type families
Copyright(c) Michael Weber <michael.weber@post.rwth-aachen.de> 2001
(c) Jeff Newbern 2003-2006
(c) Andriy Palamarchuk 2006
LicenseBSD-style (see the file LICENSE)
Maintainerross@soi.city.ac.uk
Stabilityexperimental
Portabilitynon-portable (type families)
Safe HaskellNone
LanguageGHC2021

Control.Monad.Except

Description

Computation type:
Computations which may fail or throw exceptions.
Binding strategy:
Failure records information about the cause/location of the failure. Failure values bypass the bound function, other values are used as inputs to the bound function.
Useful for:
Building computations from sequences of functions that may fail or using exception handling to structure error handling.
Zero and plus:
Zero is represented by an empty error and the plus operation executes its second argument if the first fails.
Example type:
Either String a

The Error monad (also called the Exception monad).

Synopsis

Monads with error handling

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

The strategy of combining computations that can throw exceptions by bypassing bound functions from the point an exception is thrown to the point that it is handled.

Is parameterized over the type of error information and the monad type constructor. It is common to use Either String as the monad type constructor for an error monad in which error descriptions take the form of strings. In that case and many other common cases the resulting monad is already defined as an instance of the MonadError class. You can also define your own a monad type constructor other than Either e, in which case you will have to explicitly define an instance of the MonadError class.

Associated Types

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

Methods

throwError :: ErrorType m -> m a Source #

Is used within a monadic computation to begin exception processing.

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

A handler function to handle previous errors and return to normal execution. A common idiom is:

do { action1; action2; action3 } `catchError` handler

where the action functions can call throwError. Note that handler and the do-block must have the same return type.

Instances

Instances details
MonadError IO Source # 
Instance details

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType IO 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType IO = IOError

Methods

throwError :: ErrorType IO -> IO a Source #

catchError :: IO a -> (ErrorType IO -> IO a) -> IO a Source #

MonadError (Either e) Source # 
Instance details

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (Either e) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (Either e) = e

Methods

throwError :: ErrorType (Either e) -> Either e a Source #

catchError :: Either e a -> (ErrorType (Either e) -> Either e a) -> Either e a Source #

MonadError m => MonadError (MaybeT m) Source # 
Instance details

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (MaybeT m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (MaybeT m) = ErrorType m

Methods

throwError :: ErrorType (MaybeT m) -> MaybeT m a Source #

catchError :: MaybeT m a -> (ErrorType (MaybeT m) -> MaybeT m a) -> MaybeT m a Source #

Monad m => MonadError (ExceptT e m) Source # 
Instance details

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (ExceptT e m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (ExceptT e m) = e

Methods

throwError :: ErrorType (ExceptT e m) -> ExceptT e m a Source #

catchError :: ExceptT e m a -> (ErrorType (ExceptT e m) -> ExceptT e m a) -> ExceptT e m a Source #

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

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (IdentityT m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (IdentityT m) = ErrorType m

Methods

throwError :: ErrorType (IdentityT m) -> IdentityT m a Source #

catchError :: IdentityT m a -> (ErrorType (IdentityT m) -> IdentityT m a) -> IdentityT 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 #

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

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (StateT s m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (StateT s m) = ErrorType m

Methods

throwError :: ErrorType (StateT s m) -> StateT s m a Source #

catchError :: StateT s m a -> (ErrorType (StateT s m) -> StateT s m a) -> StateT s m a Source #

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

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (StateT s m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (StateT s m) = ErrorType m

Methods

throwError :: ErrorType (StateT s m) -> StateT s m a Source #

catchError :: StateT s m a -> (ErrorType (StateT s m) -> StateT s m a) -> StateT s m a Source #

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

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (WriterT w m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (WriterT w m) = ErrorType m

Methods

throwError :: ErrorType (WriterT w m) -> WriterT w m a Source #

catchError :: WriterT w m a -> (ErrorType (WriterT w m) -> WriterT w m a) -> WriterT w m a Source #

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

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (WriterT w m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (WriterT w m) = ErrorType m

Methods

throwError :: ErrorType (WriterT w m) -> WriterT w m a Source #

catchError :: WriterT w m a -> (ErrorType (WriterT w m) -> WriterT w m a) -> WriterT w m a Source #

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

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (RWST r w s m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (RWST r w s m) = ErrorType m

Methods

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

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

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

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (RWST r w s m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (RWST r w s m) = ErrorType m

Methods

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

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

tryError :: MonadError m => m a -> m (Either (ErrorType m) a) Source #

MonadError analogue to the try function.

withError :: MonadError m => (ErrorType m -> ErrorType m) -> m a -> m a Source #

MonadError analogue to the withExceptT function. Modify the value (but not the type) of an error. The type is fixed because of the ErrorType type family.

The ExceptT monad transformer

newtype ExceptT e (m :: Type -> Type) a #

Constructors

ExceptT (m (Either e a)) 

Instances

Instances details
Functor m => Generic1 (ExceptT e m :: Type -> Type) 
Instance details

Defined in Control.Monad.Trans.Except

Associated Types

type Rep1 (ExceptT e m :: Type -> Type) 
Instance details

Defined in Control.Monad.Trans.Except

type Rep1 (ExceptT e m :: Type -> Type) = D1 ('MetaData "ExceptT" "Control.Monad.Trans.Except" "transformers-0.6.1.0-a97a" 'True) (C1 ('MetaCons "ExceptT" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (m :.: Rec1 (Either e))))

Methods

from1 :: ExceptT e m a -> Rep1 (ExceptT e m) a

to1 :: Rep1 (ExceptT e m) a -> ExceptT e m a

MonadTrans (ExceptT e) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

lift :: Monad m => m a -> ExceptT e m a #

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

Defined in Control.Monad.Trans.Except

Methods

fail :: String -> ExceptT e 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 #

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

Defined in Control.Monad.Trans.Except

Methods

liftIO :: IO a -> ExceptT e m a #

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

Defined in Control.Monad.Trans.Except

Methods

mzip :: ExceptT e m a -> ExceptT e m b -> ExceptT e m (a, b)

mzipWith :: (a -> b -> c) -> ExceptT e m a -> ExceptT e m b -> ExceptT e m c

munzip :: ExceptT e m (a, b) -> (ExceptT e m a, ExceptT e m b)

Foldable f => Foldable (ExceptT e f) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

fold :: Monoid m => ExceptT e f m -> m

foldMap :: Monoid m => (a -> m) -> ExceptT e f a -> m

foldMap' :: Monoid m => (a -> m) -> ExceptT e f a -> m

foldr :: (a -> b -> b) -> b -> ExceptT e f a -> b

foldr' :: (a -> b -> b) -> b -> ExceptT e f a -> b

foldl :: (b -> a -> b) -> b -> ExceptT e f a -> b

foldl' :: (b -> a -> b) -> b -> ExceptT e f a -> b

foldr1 :: (a -> a -> a) -> ExceptT e f a -> a

foldl1 :: (a -> a -> a) -> ExceptT e f a -> a

toList :: ExceptT e f a -> [a]

null :: ExceptT e f a -> Bool

length :: ExceptT e f a -> Int

elem :: Eq a => a -> ExceptT e f a -> Bool

maximum :: Ord a => ExceptT e f a -> a

minimum :: Ord a => ExceptT e f a -> a

sum :: Num a => ExceptT e f a -> a

product :: Num a => ExceptT e f a -> a

(Eq e, Eq1 m) => Eq1 (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

liftEq :: (a -> b -> Bool) -> ExceptT e m a -> ExceptT e m b -> Bool

(Ord e, Ord1 m) => Ord1 (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

liftCompare :: (a -> b -> Ordering) -> ExceptT e m a -> ExceptT e m b -> Ordering

(Read e, Read1 m) => Read1 (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (ExceptT e m a)

liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [ExceptT e m a]

liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (ExceptT e m a)

liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [ExceptT e m a]

(Show e, Show1 m) => Show1 (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> ExceptT e m a -> ShowS

liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [ExceptT e m a] -> ShowS

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

Defined in Control.Monad.Trans.Except

Methods

contramap :: (a' -> a) -> ExceptT e m a -> ExceptT e m a'

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

Traversable f => Traversable (ExceptT e f) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

traverse :: Applicative f0 => (a -> f0 b) -> ExceptT e f a -> f0 (ExceptT e f b)

sequenceA :: Applicative f0 => ExceptT e f (f0 a) -> f0 (ExceptT e f a)

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

sequence :: Monad m => ExceptT e f (m a) -> m (ExceptT e f a) #

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

Defined in Control.Monad.Trans.Except

Methods

empty :: ExceptT e m a

(<|>) :: ExceptT e m a -> ExceptT e m a -> ExceptT e m a

some :: ExceptT e m a -> ExceptT e m [a]

many :: ExceptT e m a -> ExceptT e m [a]

(Functor m, Monad m) => Applicative (ExceptT e m) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

pure :: a -> ExceptT e m a

(<*>) :: ExceptT e m (a -> b) -> ExceptT e m a -> ExceptT e m b

liftA2 :: (a -> b -> c) -> ExceptT e m a -> ExceptT e m b -> ExceptT e m c

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

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

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, 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 #

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

Defined in Control.Monad.Cont.Class

Methods

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

Monad m => MonadError (ExceptT e m) Source # 
Instance details

Defined in Control.Monad.Except.Class

Associated Types

type ErrorType (ExceptT e m) 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (ExceptT e m) = e

Methods

throwError :: ErrorType (ExceptT e m) -> ExceptT e m a Source #

catchError :: ExceptT e m a -> (ErrorType (ExceptT e m) -> ExceptT e m a) -> ExceptT e m a Source #

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

Defined in Control.Monad.RWS.Class

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 #

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

Defined in Control.Monad.State.Class

Associated Types

type StateType (ExceptT e m) 
Instance details

Defined in Control.Monad.State.Class

type StateType (ExceptT e m) = StateType m

Methods

get :: ExceptT e m (StateType (ExceptT e m)) Source #

put :: StateType (ExceptT e m) -> ExceptT e m () Source #

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

Defined in Control.Monad.Writer.Class

Associated Types

type WriterType (ExceptT e m) 
Instance details

Defined in Control.Monad.Writer.Class

Methods

tell :: WriterType (ExceptT e m) -> ExceptT e m () Source #

listen :: ExceptT e m a -> ExceptT e m (a, WriterType (ExceptT e m)) Source #

pass :: ExceptT e m (a, WriterType (ExceptT e m) -> WriterType (ExceptT e m)) -> ExceptT e m a Source #

Generic (ExceptT e m a) 
Instance details

Defined in Control.Monad.Trans.Except

Associated Types

type Rep (ExceptT e m a) 
Instance details

Defined in Control.Monad.Trans.Except

type Rep (ExceptT e m a) = D1 ('MetaData "ExceptT" "Control.Monad.Trans.Except" "transformers-0.6.1.0-a97a" 'True) (C1 ('MetaCons "ExceptT" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (m (Either e a)))))

Methods

from :: ExceptT e m a -> Rep (ExceptT e m a) x

to :: Rep (ExceptT e m a) x -> ExceptT e m a

(Read e, Read1 m, Read a) => Read (ExceptT e m a) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

readsPrec :: Int -> ReadS (ExceptT e m a)

readList :: ReadS [ExceptT e m a]

readPrec :: ReadPrec (ExceptT e m a)

readListPrec :: ReadPrec [ExceptT e m a]

(Show e, Show1 m, Show a) => Show (ExceptT e m a) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

showsPrec :: Int -> ExceptT e m a -> ShowS

show :: ExceptT e m a -> String

showList :: [ExceptT e m a] -> ShowS

(Eq e, Eq1 m, Eq a) => Eq (ExceptT e m a) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

(==) :: ExceptT e m a -> ExceptT e m a -> Bool

(/=) :: ExceptT e m a -> ExceptT e m a -> Bool

(Ord e, Ord1 m, Ord a) => Ord (ExceptT e m a) 
Instance details

Defined in Control.Monad.Trans.Except

Methods

compare :: ExceptT e m a -> ExceptT e m a -> Ordering

(<) :: ExceptT e m a -> ExceptT e m a -> Bool

(<=) :: ExceptT e m a -> ExceptT e m a -> Bool

(>) :: ExceptT e m a -> ExceptT e m a -> Bool

(>=) :: ExceptT e m a -> ExceptT e m a -> Bool

max :: ExceptT e m a -> ExceptT e m a -> ExceptT e m a

min :: ExceptT e m a -> ExceptT e m a -> ExceptT e m a

type Rep1 (ExceptT e m :: Type -> Type) 
Instance details

Defined in Control.Monad.Trans.Except

type Rep1 (ExceptT e m :: Type -> Type) = D1 ('MetaData "ExceptT" "Control.Monad.Trans.Except" "transformers-0.6.1.0-a97a" 'True) (C1 ('MetaCons "ExceptT" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (m :.: Rec1 (Either e))))
type ErrorType (ExceptT e m) Source # 
Instance details

Defined in Control.Monad.Except.Class

type ErrorType (ExceptT e m) = e
type EnvType (ExceptT e m) Source # 
Instance details

Defined in Control.Monad.Reader.Class

type EnvType (ExceptT e m) = EnvType m
type StateType (ExceptT e m) Source # 
Instance details

Defined in Control.Monad.State.Class

type StateType (ExceptT e m) = StateType m
type WriterType (ExceptT e m) Source # 
Instance details

Defined in Control.Monad.Writer.Class

type Rep (ExceptT e m a) 
Instance details

Defined in Control.Monad.Trans.Except

type Rep (ExceptT e m a) = D1 ('MetaData "ExceptT" "Control.Monad.Trans.Except" "transformers-0.6.1.0-a97a" 'True) (C1 ('MetaCons "ExceptT" 'PrefixI 'False) (S1 ('MetaSel ('Nothing :: Maybe Symbol) 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (m (Either e a)))))

runExceptT :: ExceptT e m a -> m (Either e a) #

mapExceptT :: (m (Either e a) -> n (Either e' b)) -> ExceptT e m a -> ExceptT e' n b #

withExceptT :: forall (m :: Type -> Type) e e' a. Functor m => (e -> e') -> ExceptT e m a -> ExceptT e' 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: Custom Error Data Type

Here is an example that demonstrates the use of a custom Error data type with the throwError and catchError exception mechanism from MonadError. The example throws an exception if the user enters an empty string or a string longer than 5 characters. Otherwise it prints length of the string.

import Control.Monad.Except

-- This is the type to represent length calculation error.
data LengthError = EmptyString  -- Entered string was empty.
          | StringTooLong Int   -- A string is longer than 5 characters.
                                -- Records a length of the string.
          | OtherError String   -- Other error, stores the problem description.

-- Converts LengthError to a readable message.
instance Show LengthError where
  show EmptyString = "The string was empty!"
  show (StringTooLong len) =
      "The length of the string (" ++ (show len) ++ ") is bigger than 5!"
  show (OtherError msg) = msg

-- For our monad type constructor, we use Either LengthError
-- which represents failure using Left LengthError
-- or a successful result of type a using Right a.
type LengthMonad = Either LengthError

main = do
  putStrLn "Please enter a string:"
  s <- getLine
  reportResult (calculateLengthOrFail s)

-- Attempts to calculate length and throws an error if the provided string is
-- empty or longer than 5 characters.
-- The processing is done in Either monad.
calculateLengthOrFail :: String -> LengthMonad Int
calculateLengthOrFail [] = throwError EmptyString
calculateLengthOrFail s | len > 5 = throwError (StringTooLong len)
                        | otherwise = return len
  where len = length s

-- Prints result of the string length calculation.
reportResult :: LengthMonad Int -> IO ()
reportResult (Right len) = putStrLn ("The length of the string is " ++ (show len))
reportResult (Left e) = putStrLn ("Length calculation failed with error: " ++ (show e))

Example 2: Using ExceptT Monad Transformer

ErrorT monad transformer can be used to add error handling to another monad. Here is an example how to combine it with an IO monad:

import Control.Monad.Except

-- An IO monad which can return String failure.
-- It is convenient to define the monad type of the combined monad,
-- especially if we combine more monad transformers.
type LengthMonad = ExceptT String IO

main = do
  -- runExceptT removes the ExceptT wrapper
  r <- runExceptT calculateLength
  reportResult r

-- Asks user for a non-empty string and returns its length.
-- Throws an error if user enters an empty string.
calculateLength :: LengthMonad Int
calculateLength = do
  -- all the IO operations have to be lifted to the IO monad in the monad stack
  liftIO $ putStrLn "Please enter a non-empty string: "
  s <- liftIO getLine
  if null s
    then throwError "The string was empty!"
    else return $ length s

-- Prints result of the string length calculation.
reportResult :: Either String Int -> IO ()
reportResult (Right len) = putStrLn ("The length of the string is " ++ (show len))
reportResult (Left e) = putStrLn ("Length calculation failed with error: " ++ (show e))