Safe Haskell	Safe
Language	Haskell98

Network.Gitit.Compat.Except

Synopsis

data ExceptT e (m :: * -> *) a
type Except e = ExceptT e Identity
class Error a where
runExceptT :: ExceptT e m a -> m (Either e a)
runExcept :: Except e a -> Either e a
class Monad m => MonadError e (m :: * -> *) | m -> e
throwError :: MonadError e m => e -> m a
catchError :: MonadError e m => m a -> (e -> m a) -> m a

Documentation

data 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.

Instances

MonadReader r m => MonadReader r (ExceptT e m)	Since: mtl-2.2
Instance details Defined in Control.Monad.Reader.Class Methods ask :: ExceptT e m r # local :: (r -> r) -> ExceptT e m a -> ExceptT e m a # reader :: (r -> a) -> ExceptT e m a #
FilterMonad a m => FilterMonad a (ExceptT e m)
Instance details Defined in Happstack.Server.Internal.Monads Methods setFilter :: (a -> a) -> ExceptT e m () # composeFilter :: (a -> a) -> ExceptT e m () # getFilter :: ExceptT e m b -> ExceptT e m (b, a -> a) #
WebMonad a m => WebMonad a (ExceptT e m)
Instance details Defined in Happstack.Server.Internal.Monads Methods finishWith :: a -> ExceptT e m b #
MonadBaseControl b m => MonadBaseControl b (ExceptT e m)
Instance details Defined in Control.Monad.Trans.Control Associated Types type StM (ExceptT e m) a :: * # Methods liftBaseWith :: (RunInBase (ExceptT e m) b -> b a) -> ExceptT e m a # restoreM :: StM (ExceptT e m) a -> ExceptT e m a #
MonadState s m => MonadState s (ExceptT e m)	Since: mtl-2.2
Instance details Defined in Control.Monad.State.Class Methods get :: ExceptT e m s # put :: s -> ExceptT e m () # state :: (s -> (a, s)) -> ExceptT e m a #
Monad m => MonadError e (ExceptT e m)	Since: mtl-2.2
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> ExceptT e m a # catchError :: ExceptT e m a -> (e -> 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 #
MonadTransControl (ExceptT e)
Instance details Defined in Control.Monad.Trans.Control Associated Types type StT (ExceptT e) a :: * # Methods liftWith :: Monad m => (Run (ExceptT e) -> m a) -> ExceptT e m a # restoreT :: Monad m => m (StT (ExceptT e) a) -> 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 # fail :: String -> 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 #
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 #
MonadFail m => MonadFail (ExceptT e m)
Instance details Defined in Control.Monad.Trans.Except Methods fail :: String -> 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 #
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 # 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)
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) #
(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 #
(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] #
(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 #
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) #
MonadIO m => MonadIO (ExceptT e m)
Instance details Defined in Control.Monad.Trans.Except Methods liftIO :: IO a -> ExceptT e m a #
MonadResource m => MonadResource (ExceptT e m)
Instance details Defined in Control.Monad.Trans.Resource.Internal Methods liftResourceT :: ResourceT IO a -> ExceptT e m a #
PrimMonad m => PrimMonad (ExceptT e m)
Instance details Defined in Control.Monad.Primitive Associated Types type PrimState (ExceptT e m) :: * # Methods primitive :: (State# (PrimState (ExceptT e m)) -> (#State# (PrimState (ExceptT e m)), a#)) -> ExceptT e m a #
(Monad m, HasDynFlags m) => HasDynFlags (ExceptT e m)
Instance details Defined in DynFlags Methods getDynFlags :: ExceptT e m DynFlags #
(Happstack m, Monoid e) => Happstack (ExceptT e m)
Instance details Defined in Happstack.Server.Monads
(Monad m, HasRqData m) => HasRqData (ExceptT e m)
Instance details Defined in Happstack.Server.RqData Methods askRqEnv :: ExceptT e m RqEnv # localRqEnv :: (RqEnv -> RqEnv) -> ExceptT e m a -> ExceptT e m a # rqDataError :: Errors String -> ExceptT e m a #
ServerMonad m => ServerMonad (ExceptT e m)
Instance details Defined in Happstack.Server.Internal.Monads Methods askRq :: ExceptT e m Request # localRq :: (Request -> Request) -> ExceptT e m a -> ExceptT e m a #
(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 #
(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 #
type StT (ExceptT e) a
Instance details Defined in Control.Monad.Trans.Control type StT (ExceptT e) a = Either e a
type PrimState (ExceptT e m)
Instance details Defined in Control.Monad.Primitive type PrimState (ExceptT e m) = PrimState m
type StM (ExceptT e m) a
Instance details Defined in Control.Monad.Trans.Control type StM (ExceptT e m) a = ComposeSt (ExceptT e) m 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.

class Error a where Source #

Methods

noMsg :: a Source #

strMsg :: String -> a Source #

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

The inverse of ExceptT.

runExcept :: Except e a -> Either e a #

Extractor for computations in the exception monad. (The inverse of except).

class Monad m => MonadError e (m :: * -> *) | m -> e #

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 error type and/or use a monad type constructor other than Either String or Either IOError. In these cases you will have to explicitly define instances of the MonadError class. (If you are using the deprecated Control.Monad.Error or Control.Monad.Trans.Error, you may also have to define an Error instance.)

Minimal complete definition

throwError, catchError

Instances

MonadError () Maybe	Since: mtl-2.2.2
Instance details Defined in Control.Monad.Error.Class Methods throwError :: () -> Maybe a # catchError :: Maybe a -> (() -> Maybe a) -> Maybe a #
MonadError String TokenizerM
Instance details Defined in Skylighting.Tokenizer Methods throwError :: String -> TokenizerM a # catchError :: TokenizerM a -> (String -> TokenizerM a) -> TokenizerM a #
MonadError IOException IO
Instance details Defined in Control.Monad.Error.Class Methods throwError :: IOException -> IO a # catchError :: IO a -> (IOException -> IO a) -> IO a #
MonadError PandocError PandocIO
Instance details Defined in Text.Pandoc.Class Methods throwError :: PandocError -> PandocIO a # catchError :: PandocIO a -> (PandocError -> PandocIO a) -> PandocIO a #
MonadError PandocError PandocPure
Instance details Defined in Text.Pandoc.Class Methods throwError :: PandocError -> PandocPure a # catchError :: PandocPure a -> (PandocError -> PandocPure a) -> PandocPure a #
MonadError e m => MonadError e (ResourceT m)
Instance details Defined in Control.Monad.Trans.Resource.Internal Methods throwError :: e -> ResourceT m a # catchError :: ResourceT m a -> (e -> ResourceT m a) -> ResourceT m a #
MonadError e m => MonadError e (WebT m)
Instance details Defined in Happstack.Server.Internal.Monads Methods throwError :: e -> WebT m a # catchError :: WebT m a -> (e -> WebT m a) -> WebT m a #
(Monad m, MonadError e m) => MonadError e (ServerPartT m)
Instance details Defined in Happstack.Server.Internal.Monads Methods throwError :: e -> ServerPartT m a # catchError :: ServerPartT m a -> (e -> ServerPartT m a) -> ServerPartT m a #
MonadError e m => MonadError e (MaybeT m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> MaybeT m a # catchError :: MaybeT m a -> (e -> MaybeT m a) -> MaybeT m a #
MonadError e m => MonadError e (ListT m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> ListT m a # catchError :: ListT m a -> (e -> ListT m a) -> ListT m a #
MonadError e (Either e)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> Either e a # catchError :: Either e a -> (e -> Either e a) -> Either e a #
(Monoid w, MonadError e m) => MonadError e (WriterT w m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> WriterT w m a # catchError :: WriterT w m a -> (e -> WriterT w m a) -> WriterT w m a #
(Monoid w, MonadError e m) => MonadError e (WriterT w m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> WriterT w m a # catchError :: WriterT w m a -> (e -> WriterT w m a) -> WriterT w m a #
MonadError e m => MonadError e (StateT s m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> StateT s m a # catchError :: StateT s m a -> (e -> StateT s m a) -> StateT s m a #
MonadError e m => MonadError e (StateT s m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> StateT s m a # catchError :: StateT s m a -> (e -> StateT s m a) -> StateT s m a #
MonadError e m => MonadError e (IdentityT m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> IdentityT m a # catchError :: IdentityT m a -> (e -> IdentityT m a) -> IdentityT m a #
Monad m => MonadError e (ExceptT e m)	Since: mtl-2.2
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> ExceptT e m a # catchError :: ExceptT e m a -> (e -> ExceptT e m a) -> ExceptT e m a #
(Monad m, Error e) => MonadError e (ErrorT e m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> ErrorT e m a # catchError :: ErrorT e m a -> (e -> ErrorT e m a) -> ErrorT e m a #
MonadError e m => MonadError e (ParsecT s u m)
Instance details Defined in Text.Parsec.Prim Methods throwError :: e -> ParsecT s u m a # catchError :: ParsecT s u m a -> (e -> ParsecT s u m a) -> ParsecT s u m a #
MonadError e m => MonadError e (ConduitT i o m)
Instance details Defined in Data.Conduit.Internal.Conduit Methods throwError :: e -> ConduitT i o m a # catchError :: ConduitT i o m a -> (e -> ConduitT i o m a) -> ConduitT i o m a #
MonadError e m => MonadError e (ReaderT r m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> ReaderT r m a # catchError :: ReaderT r m a -> (e -> ReaderT r m a) -> ReaderT r m a #
(Monoid w, MonadError e m) => MonadError e (RWST r w s m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> RWST r w s m a # catchError :: RWST r w s m a -> (e -> RWST r w s m a) -> RWST r w s m a #
(Monoid w, MonadError e m) => MonadError e (RWST r w s m)
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> RWST r w s m a # catchError :: RWST r w s m a -> (e -> RWST r w s m a) -> RWST r w s m a #
MonadError e m => MonadError e (Pipe l i o u m)
Instance details Defined in Data.Conduit.Internal.Pipe Methods throwError :: e -> Pipe l i o u m a # catchError :: Pipe l i o u m a -> (e -> Pipe l i o u m a) -> Pipe l i o u m a #

throwError :: MonadError e m => e -> m a #

Is used within a monadic computation to begin exception processing.

catchError :: MonadError e m => 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.