Control.Monad.Constrained.Error

This module is a duplication of the Control.Monad.Error module from the mtl, for constrained monads.

Documentation

class Monad m => MonadError e m | m -> e where

A class for monads which can error out.

Minimal complete definition

throwError, catchError

Associated Types

type SuitableError m a :: Constraint

Methods

throwError :: SuitableError m a => e -> m a

Raise an error.

catchError :: SuitableError m a => m a -> (e -> m a) -> m a

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

(MonadError e m, Monad (Unconstrained m)) => MonadError e (MaybeT m)

Associated Types

type SuitableError (MaybeT m :: * -> *) a :: Constraint

Methods

throwError :: SuitableError (MaybeT m) a => e -> MaybeT m a

catchError :: SuitableError (MaybeT m) a => MaybeT m a -> (e -> MaybeT m a) -> MaybeT m a

MonadError e (Either e)

Associated Types

type SuitableError (Either e :: * -> *) a :: Constraint

Methods

throwError :: SuitableError (Either e) a => e -> Either e a

catchError :: SuitableError (Either e) a => Either e a -> (e -> Either e a) -> Either e a

(MonadError e m, Monad (Unconstrained m)) => MonadError e (StateT s m)

Associated Types

type SuitableError (StateT s m :: * -> *) a :: Constraint

Methods

throwError :: SuitableError (StateT s m) a => e -> StateT s m a

catchError :: SuitableError (StateT s m) a => StateT s m a -> (e -> StateT s m a) -> StateT s m a

(MonadError e m, Monad (Unconstrained m)) => MonadError e (StateT s m)

Associated Types

type SuitableError (StateT s m :: * -> *) a :: Constraint

Methods

throwError :: SuitableError (StateT s m) a => e -> StateT s m a

catchError :: SuitableError (StateT s m) a => StateT s m a -> (e -> StateT s m a) -> StateT s m a

MonadError e m => MonadError e (IdentityT * m)

Associated Types

type SuitableError (IdentityT * m :: * -> *) a :: Constraint

Methods

throwError :: SuitableError (IdentityT * m) a => e -> IdentityT * m a

catchError :: SuitableError (IdentityT * m) a => IdentityT * m a -> (e -> IdentityT * m a) -> IdentityT * m a

(Monad m, Monad (Unconstrained m)) => MonadError e (ExceptT e m)

Associated Types

type SuitableError (ExceptT e m :: * -> *) a :: Constraint

Methods

throwError :: SuitableError (ExceptT e m) a => e -> ExceptT e m a

catchError :: SuitableError (ExceptT e m) a => ExceptT e m a -> (e -> ExceptT e m a) -> ExceptT e m a

(MonadError e m, Monad (Unconstrained m)) => MonadError e (WriterT w m)

Associated Types

type SuitableError (WriterT w m :: * -> *) a :: Constraint

Methods

throwError :: SuitableError (WriterT w m) a => e -> WriterT w m a

catchError :: SuitableError (WriterT w m) a => WriterT w m a -> (e -> WriterT w m a) -> WriterT w m a

MonadError e m => MonadError e (ReaderT * r m)

Associated Types

type SuitableError (ReaderT * r m :: * -> *) a :: Constraint

Methods

throwError :: SuitableError (ReaderT * r m) a => e -> ReaderT * r m a

catchError :: SuitableError (ReaderT * r m) a => ReaderT * r m a -> (e -> ReaderT * r m a) -> ReaderT * r m a

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

A monad transformer that adds exceptions to other monads.

ExceptT constructs a monad parameterized over two things:

• e - The exception type.
• m - The inner monad.

The return function yields a computation that produces the given value, while >>= sequences two subcomputations, exiting on the first exception.

Constructors

ExceptT (m (Either e a))

Instances

(Monad m, Monad (Unconstrained m)) => MonadError e (ExceptT e m)

Associated Types

type SuitableError (ExceptT e m :: * -> *) a :: Constraint

Methods

throwError :: SuitableError (ExceptT e m) a => e -> ExceptT e m a

catchError :: SuitableError (ExceptT e m) a => ExceptT e m a -> (e -> ExceptT e m a) -> ExceptT e m a

(MonadReader r m, Monad (Unconstrained m)) => MonadReader r (ExceptT e m)

Associated Types

type ReaderSuitable (ExceptT e m :: * -> *) a :: Constraint

Methods

ask :: ExceptT e m r

local :: (ReaderSuitable (ExceptT e m) a, ReaderSuitable (ExceptT e m) r) => (r -> r) -> ExceptT e m a -> ExceptT e m a

reader :: (ReaderSuitable (ExceptT e m) r, ReaderSuitable (ExceptT e m) a) => (r -> a) -> ExceptT e m a

(MonadState s m, Monad (Unconstrained m)) => MonadState s (ExceptT e m)

Associated Types

type StateSuitable (ExceptT e m :: * -> *) a :: Constraint

Methods

get :: ExceptT e m s

put :: s -> ExceptT e m ()

state :: (StateSuitable (ExceptT e m) a, StateSuitable (ExceptT e m) s) => (s -> (a, s)) -> ExceptT e m a

(MonadWriter w m, Monad (Unconstrained m)) => MonadWriter w (ExceptT e m)

Associated Types

type WriterSuitable (ExceptT e m :: * -> *) a :: Constraint

Methods

writer :: WriterSuitable (ExceptT e m) a => (a, w) -> ExceptT e m a

tell :: w -> ExceptT e m ()

listenC :: WriterSuitable (ExceptT e m) b => (a -> w -> b) -> ExceptT e m a -> ExceptT e m b

passC :: WriterSuitable (ExceptT e m) a => (a -> w -> w) -> ExceptT e m a -> ExceptT e m a

MonadTrans (ExceptT e)

Methods

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

MonadTrans (ExceptT e)

Associated Types

type SuitableLift (ExceptT e :: (* -> *) -> * -> *) (m :: * -> *) a :: Constraint

Methods

lift :: (Monad m, SuitableLift (ExceptT e) m a) => m a -> ExceptT e m a

Monad m => Monad (ExceptT e m)

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

fail :: String -> ExceptT e m a

Functor m => Functor (ExceptT e m)

Methods

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

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

MonadFix m => MonadFix (ExceptT e m)

Methods

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

MonadFail m => MonadFail (ExceptT e m)

Methods

fail :: String -> ExceptT e m a

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

Methods

pure :: a -> ExceptT e m a

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

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

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

Foldable f => Foldable (ExceptT e f)

Methods

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

Traversable f => Traversable (ExceptT e f)

Methods

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

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

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

Methods

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

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

Methods

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

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

Methods

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

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

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

Methods

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

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

MonadZip m => MonadZip (ExceptT e m)

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)

MonadIO m => MonadIO (ExceptT e m)

Methods

liftIO :: IO a -> ExceptT e m a

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

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]

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

Methods

mzero :: ExceptT e m a

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

(Monad m, Monoid e, Monad (Unconstrained m)) => Alternative (ExceptT e m)

Methods

empty :: Suitable (ExceptT e m) a => ExceptT e m a

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

some :: Suitable (ExceptT e m) [a] => ExceptT e m a -> ExceptT e m [a]

many :: Suitable (ExceptT e m) [a] => ExceptT e m a -> ExceptT e m [a]

(Monad m, IsString e, Monad (Unconstrained m)) => MonadFail (ExceptT e m)

Methods

fail :: Suitable (ExceptT e m) a => String -> ExceptT e m a

(Monad m, Monad (Unconstrained m)) => Monad (ExceptT e m)

Methods

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

(Monad m, Monad (Unconstrained m)) => Applicative (ExceptT e m)

Associated Types

type Unconstrained (ExceptT e m :: * -> *) :: * -> *

Methods

reflect :: ExceptT e m a -> Unconstrained (ExceptT e m) a

reify :: Suitable (ExceptT e m) a => Unconstrained (ExceptT e m) a -> ExceptT e m a

pure :: Suitable (ExceptT e m) a => a -> ExceptT e m a

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

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

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

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

liftA3 :: Suitable (ExceptT e m) d => (a -> b -> c -> d) -> ExceptT e m a -> ExceptT e m b -> ExceptT e m c -> ExceptT e m d

Functor m => Functor (ExceptT e m)

Associated Types

type Suitable (ExceptT e m :: * -> *) a :: Constraint

Methods

fmap :: Suitable (ExceptT e m) b => (a -> b) -> ExceptT e m a -> ExceptT e m b

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

(Monad m, IsString e) => MonadFail (ExceptT e m)

Methods

fail :: Suitable (ExceptT e m) a => String -> ExceptT e m a

Monad m => Monad (ExceptT e m)

Associated Types

type Suitable (ExceptT e m :: * -> *) a :: Constraint

Methods

(>>=) :: (Suitable (ExceptT e m) a, Suitable (ExceptT e m) b) => ExceptT e m a -> (a -> ExceptT e m b) -> ExceptT e m b

join :: Suitable (ExceptT e m) a => ExceptT e m (ExceptT e m a) -> ExceptT e m a

(MonadCont m, Monad (Unconstrained m)) => MonadCont (ExceptT e m)

Methods

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

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

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)

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

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

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)

Methods

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

show :: ExceptT e m a -> String

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

type SuitableLift (ExceptT e) m a

type SuitableLift (ExceptT e) m a = Suitable m (Either e a)

type Unconstrained (ExceptT e m)

type Unconstrained (ExceptT e m) = ExceptT e (Unconstrained m)

type Suitable (ExceptT e m) a

type Suitable (ExceptT e m) a = Suitable m (Either e a)

type Suitable (ExceptT e m) a

type Suitable (ExceptT e m) a = ()

type SuitableError (ExceptT e m) a

type SuitableError (ExceptT e m) a = Suitable m (Either e a)

type ReaderSuitable (ExceptT e m) a

type ReaderSuitable (ExceptT e m) a = (ReaderSuitable m a, Suitable m (Either e a), ReaderSuitable m (Either e a))

type StateSuitable (ExceptT e m) a

type StateSuitable (ExceptT e m) a = (Suitable m (Either e a), StateSuitable m a)

type WriterSuitable (ExceptT e m) a

type WriterSuitable (ExceptT e m) a = (WriterSuitable m a, WriterSuitable m (Either e a), Suitable m (Either e a))

type Except e = ExceptT e Identity

The parameterizable exception monad.

Computations are either exceptions or normal values.

The return function returns a normal value, while >>= exits on the first exception. For a variant that continues after an error and collects all the errors, see Errors.