The AnnotatedException type wraps an exception with a [Annotation]. This can provide a sort of a manual stack trace with programmer provided data.

Since: 0.1.0.0

Attach an empty [Annotation] to an exception.

Since: 0.1.0.0

Like throwWithCallStack, but uses MonadIO instead of MonadThrow.

Since: 0.1.2.0

Like checkpoint, but uses MonadUnliftIO instead of MonadCatch.

Since: 0.1.2.0

Like checkpointMany, but uses MonadUnliftIO instead of MonadCatch.

Since: 0.1.2.0

Add the current CallStack to the checkpoint. This function searches any thrown exception for a pre-existing CallStack and will not overwrite or replace the CallStack if one is already present.

Primarily useful when you're wrapping a third party library.

Since: 0.1.0.0

Like checkpointCallStackWith, but uses MonadUnliftIO instead of MonadCatch.

Since: 0.1.2.0

Like catch, but uses MonadUnliftIO instead of MonadCatch.

Since: 0.1.2.0

Like catches, bt uses MonadUnliftIO instead of MonadCatch.

Since: 0.1.2.0

Like tryAnnotated but uses MonadUnliftIO instead of MonadCatch.

Since: 0.1.2.0

Like try but uses MonadUnliftIO instead of MonadCatch.

Since: 0.1.2.0

Call fromException on the underlying Exception, attaching the annotations to the result.

Since: 0.1.0.0

Call toException on the underlying Exception.

Since: 0.1.0.0

Retrieves the CallStack from an AnnotatedException if one is present.

Since: 0.1.0.0

Adds a CallStack to the given AnnotatedException. This function will search through the existing annotations, and it will not add a second CallStack to the list.

Since: 0.1.0.0

An Annotation is a wrapper around a value that includes a Typeable constraint so we can later unpack it. It is essentially a 'Dynamic, but we also include Show and Eq so it's more useful.

Since: 0.1.0.0

A wrapper type for putting a CallStack into an Annotation. We need this because CallStack does not have an Eq instance.

Since: 0.1.0.0

Any type that you wish to throw or catch as an exception must be an instance of the Exception class. The simplest case is a new exception type directly below the root:

data MyException = ThisException | ThatException
    deriving Show

instance Exception MyException

The default method definitions in the Exception class do what we need in this case. You can now throw and catch ThisException and ThatException as exceptions:

*Main> throw ThisException `catch` \e -> putStrLn ("Caught " ++ show (e :: MyException))
Caught ThisException

In more complicated examples, you may wish to define a whole hierarchy of exceptions:

---------------------------------------------------------------------
-- Make the root exception type for all the exceptions in a compiler

data SomeCompilerException = forall e . Exception e => SomeCompilerException e

instance Show SomeCompilerException where
    show (SomeCompilerException e) = show e

instance Exception SomeCompilerException

compilerExceptionToException :: Exception e => e -> SomeException
compilerExceptionToException = toException . SomeCompilerException

compilerExceptionFromException :: Exception e => SomeException -> Maybe e
compilerExceptionFromException x = do
    SomeCompilerException a <- fromException x
    cast a

---------------------------------------------------------------------
-- Make a subhierarchy for exceptions in the frontend of the compiler

data SomeFrontendException = forall e . Exception e => SomeFrontendException e

instance Show SomeFrontendException where
    show (SomeFrontendException e) = show e

instance Exception SomeFrontendException where
    toException = compilerExceptionToException
    fromException = compilerExceptionFromException

frontendExceptionToException :: Exception e => e -> SomeException
frontendExceptionToException = toException . SomeFrontendException

frontendExceptionFromException :: Exception e => SomeException -> Maybe e
frontendExceptionFromException x = do
    SomeFrontendException a <- fromException x
    cast a

---------------------------------------------------------------------
-- Make an exception type for a particular frontend compiler exception

data MismatchedParentheses = MismatchedParentheses
    deriving Show

instance Exception MismatchedParentheses where
    toException   = frontendExceptionToException
    fromException = frontendExceptionFromException

We can now catch a MismatchedParentheses exception as MismatchedParentheses, SomeFrontendException or SomeCompilerException, but not other types, e.g. IOException:

*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeFrontendException))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: SomeCompilerException))
Caught MismatchedParentheses
*Main> throw MismatchedParentheses `catch` \e -> putStrLn ("Caught " ++ show (e :: IOException))
*** Exception: MismatchedParentheses

The SomeException type is the root of the exception type hierarchy. When an exception of type e is thrown, behind the scenes it is encapsulated in a SomeException.

Like throw, but uses MonadIO instead of MonadThrow.

Since: 0.1.2.0

Generalized version of Handler

Monads in which IO computations may be embedded. Any monad built by applying a sequence of monad transformers to the IO monad will be an instance of this class.

Instances should satisfy the following laws, which state that liftIO is a transformer of monads:

• liftIO . return = return

• liftIO (m >>= f) = liftIO m >>= (liftIO . f)

Monads which allow their actions to be run in IO.

While MonadIO allows an IO action to be lifted into another monad, this class captures the opposite concept: allowing you to capture the monadic context. Note that, in order to meet the laws given below, the intuition is that a monad must have no monadic state, but may have monadic context. This essentially limits MonadUnliftIO to ReaderT and IdentityT transformers on top of IO.

Laws. For any value u returned by askUnliftIO, it must meet the monad transformer laws as reformulated for MonadUnliftIO:

• unliftIO u . return = return

• unliftIO u (m >>= f) = unliftIO u m >>= unliftIO u . f

Instances of MonadUnliftIO must also satisfy the idempotency law:

• askUnliftIO >>= \u -> (liftIO . unliftIO u) m = m

This law showcases two properties. First, askUnliftIO doesn't change the monadic context, and second, liftIO . unliftIO u is equivalent to id IF called in the same monadic context as askUnliftIO.

Since: unliftio-core-0.1.0.0