Safe Haskell | Safe |
---|---|
Language | Haskell98 |
Wrapper for Control.Monad.Except from the mtl package
- class Error a where
- data ExceptT e m a :: * -> (* -> *) -> * -> *
- mkExceptT :: m (Either e a) -> ExceptT e m a
- class Monad m => MonadError e m | m -> e where
- throwError :: e -> m a
- catchError :: m a -> (e -> m a) -> m 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
Documentation
Nothing
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.
HasOptions NLM Source | |
MonadEquiv c v d m => MonadEquiv c v d (ExceptT e m) | |
MonadWriter w m => MonadWriter w (ExceptT e m) | |
MonadState s m => MonadState s (ExceptT e m) | |
MonadReader r m => MonadReader r (ExceptT e m) | |
Monad m => MonadError e (ExceptT e m) | |
MonadTrans (ExceptT e) | |
Monad m => Monad (ExceptT e m) | |
Functor m => Functor (ExceptT e m) | |
MonadFix m => MonadFix (ExceptT e m) | |
(Functor m, Monad m) => Applicative (ExceptT e m) | |
Foldable f => Foldable (ExceptT e f) | |
Traversable f => Traversable (ExceptT e f) | |
(Functor m, Monad m, Monoid e) => Alternative (ExceptT e m) | |
(Monad m, Monoid e) => MonadPlus (ExceptT e m) | |
MonadIO m => MonadIO (ExceptT e m) | |
(Eq e, Eq1 m) => Eq1 (ExceptT e m) | |
(Ord e, Ord1 m) => Ord1 (ExceptT e m) | |
(Read e, Read1 m) => Read1 (ExceptT e m) | |
(Show e, Show1 m) => Show1 (ExceptT e m) | |
PrimMonad m => PrimMonad (ExceptT e m) | |
MonadTCM tcm => MonadTCM (ExceptT err tcm) Source | |
(Eq e, Eq1 m, Eq a) => Eq (ExceptT e m a) | |
(Ord e, Ord1 m, Ord a) => Ord (ExceptT e m a) | |
(Read e, Read1 m, Read a) => Read (ExceptT e m a) | |
(Show e, Show1 m, Show a) => Show (ExceptT e m a) | |
type PrimState (ExceptT e m) = PrimState m |
mkExceptT :: m (Either e a) -> ExceptT e m a Source
We cannot define data constructors synonymous, so we define the
mkExceptT
function to be used instead of the data constructor
ExceptT
.
class Monad m => MonadError e m | m -> e where
throwError :: e -> m a
catchError :: m a -> (e -> m a) -> m a
MonadError IOException IO | |
MonadError ParseError Parser | |
MonadError TCErr IM | |
MonadError TCErr TerM | |
MonadError e m => MonadError e (MaybeT m) | |
MonadError e m => MonadError e (ListT m) | |
MonadError e m => MonadError e (IdentityT m) | |
MonadError e (Either e) | |
MonadError TCErr (TCMT IO) | |
(Monoid w, MonadError e m) => MonadError e (WriterT w m) | |
(Monoid w, MonadError e m) => MonadError e (WriterT w m) | |
MonadError e m => MonadError e (StateT s m) | |
MonadError e m => MonadError e (StateT s m) | |
MonadError e m => MonadError e (ReaderT r m) | |
Monad m => MonadError e (ExceptT e m) | |
(Monad m, Error e) => MonadError e (ErrorT e m) | |
(Error err, MonadError err' m) => MonadError err' (ExceptionT err m) | |
(Monoid w, MonadError e m) => MonadError e (RWST r w s m) | |
(Monoid w, MonadError e m) => MonadError e (RWST r w s m) | |
MonadError e m => MonadError e (EquivT s c v m) |
runExceptT :: ExceptT e m a -> m (Either e a)
The inverse of ExceptT
.
mapExceptT :: (m (Either e a) -> n (Either e' b)) -> ExceptT e m a -> ExceptT e' n b
Map the unwrapped computation using the given function.
runExceptT
(mapExceptT
f m) = f (runExceptT
m)