Safe Haskell	Safe
Language	Haskell98

Network.Gitit.Compat.Except

Synopsis

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

MonadBaseControl b m => MonadBaseControl b (ExceptT e m)
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 #
MonadReader r m => MonadReader r (ExceptT e m)
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)
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)
Methods finishWith :: a -> ExceptT e m b #
Monad m => MonadError e (ExceptT e m)
Methods throwError :: e -> ExceptT e m a # catchError :: ExceptT e m a -> (e -> ExceptT e m a) -> ExceptT e m a #
MonadState s m => MonadState s (ExceptT e m)
Methods get :: ExceptT e m s # put :: s -> ExceptT e m () # state :: (s -> (a, s)) -> ExceptT e m a #
MonadTrans (ExceptT e)
Methods lift :: Monad m => m a -> ExceptT e m a #
MonadTransControl (ExceptT e)
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)
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) #
(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 #
(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 #
(Monad m, HasDynFlags m) => HasDynFlags (ExceptT e m)
Methods getDynFlags :: ExceptT e m DynFlags #
(Happstack m, Monoid e) => Happstack (ExceptT e m)

(Monad m, HasRqData m) => HasRqData (ExceptT e m)
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)
Methods askRq :: ExceptT e m Request # localRq :: (Request -> Request) -> ExceptT e m a -> ExceptT e m a #
MonadResource m => MonadResource (ExceptT e m)
Methods liftResourceT :: ResourceT IO a -> ExceptT e m a #
PrimMonad m => PrimMonad (ExceptT e m)
Associated Types type PrimState (ExceptT e m :: * -> ) :: # Methods primitive :: (State# (PrimState (ExceptT e m)) -> (#VoidRep, PtrRepLifted, State# (PrimState (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 StT (ExceptT e) a
type StT (ExceptT e) a = Either e a
type PrimState (ExceptT e m)
type PrimState (ExceptT e m) = PrimState m
type StM (ExceptT e m) a
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 where #

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 Error and/or MonadError classes.

Minimal complete definition

throwError, catchError

Methods

throwError :: e -> m a #

Is used within a monadic computation to begin exception processing.

catchError :: 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 IOException IO
Methods throwError :: IOException -> IO a # catchError :: IO a -> (IOException -> IO a) -> IO a #
MonadError e m => MonadError e (MaybeT m)
Methods throwError :: e -> MaybeT m a # catchError :: MaybeT m a -> (e -> MaybeT m a) -> MaybeT m a #
MonadError e m => MonadError e (ListT m)
Methods throwError :: e -> ListT m a # catchError :: ListT m a -> (e -> ListT m a) -> ListT m a #
MonadError e (Either e)
Methods throwError :: e -> Either e a # catchError :: Either e a -> (e -> Either e a) -> Either e a #
MonadError e m => MonadError e (ResourceT m)
Methods throwError :: e -> ResourceT m a # catchError :: ResourceT m a -> (e -> ResourceT m a) -> ResourceT m a #
MonadError e m => MonadError e (WebT m)
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)
Methods throwError :: e -> ServerPartT m a # catchError :: ServerPartT m a -> (e -> ServerPartT m a) -> ServerPartT m a #
(Monoid w, MonadError e m) => MonadError e (WriterT w m)
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)
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)
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)
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)
Methods throwError :: e -> IdentityT * m a # catchError :: IdentityT * m a -> (e -> IdentityT * m a) -> IdentityT * m a #
Monad m => MonadError e (ExceptT e m)
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)
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 (ReaderT * r m)
Methods throwError :: e -> ReaderT * r m a # catchError :: ReaderT * r m a -> (e -> ReaderT * r m a) -> ReaderT * r m a #
MonadError e m => MonadError e (ParsecT s u m)
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 #
(Monoid w, MonadError e m) => MonadError e (RWST r w s m)
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)
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 #

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

Is used within a monadic computation to begin exception processing.

catchError :: MonadError e m => forall 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.