| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Agda.Utils.Except
Description
Wrapper for Control.Monad.Except from the mtl library (>= 2.2.1)
Synopsis
- class Error a where
- data ExceptT e (m :: Type -> Type) a
- mapExceptT :: (m (Either e a) -> n (Either e' b)) -> ExceptT e m a -> ExceptT e' n b
- mkExceptT :: m (Either e a) -> ExceptT e m a
- class Monad m => MonadError e (m :: Type -> Type) | m -> e where
- throwError :: e -> m a
- catchError :: m a -> (e -> m a) -> m a
- runExceptT :: ExceptT e m a -> m (Either e a)
Documentation
Error class for backward compatibility (from Control.Monad.Trans.Error in transformers 0.3.0.0).
Minimal complete definition
Nothing
data ExceptT e (m :: Type -> Type) 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
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(mapExceptTf m) = f (runExceptTm)
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 :: Type -> Type) | 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 StringMonadError class.
You can also define your own error type and/or use a monad type constructor
other than Either StringEither IOErrorMonadError
class.
(If you are using the deprecated Control.Monad.Error or
Control.Monad.Trans.Error, you may also have to define an Error instance.)
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` handlerwhere the action functions can call throwError.
Note that handler and the do-block must have the same return type.
Instances
runExceptT :: ExceptT e m a -> m (Either e a) #
The inverse of ExceptT.