UnliftIO.Exception

Unlifted Control.Exception, with extra async exception safety and more helper functions.

Throwing

throwIO :: (MonadIO m, Exception e) => e -> m a

Synchronously throw the given exception

Since: 0.1.0.0

throwString :: (MonadIO m, HasCallStack) => String -> m a

A convenience function for throwing a user error. This is useful for cases where it would be too high a burden to define your own exception type.

This throws an exception of type StringException. When GHC supports it (base 4.9 and GHC 8.0 and onward), it includes a call stack.

Since: 0.1.0.0

data StringException

Exception type thrown by throwString.

Note that the second field of the data constructor depends on GHC/base version. For base 4.9 and GHC 8.0 and later, the second field is a call stack. Previous versions of GHC and base do not support call stacks, and the field is simply unit (provided to make pattern matching across GHC versions easier).

Since: 0.1.5.0

Constructors

StringException String CallStack

Instances

Show StringException

Methods

showsPrec :: Int -> StringException -> ShowS

show :: StringException -> String

showList :: [StringException] -> ShowS

Exception StringException

Methods

toException :: StringException -> SomeException

fromException :: SomeException -> Maybe StringException

displayException :: StringException -> String

stringException :: HasCallStack => String -> StringException

Smart constructor for a StringException that deals with the call stack.

Since: 0.1.0.0

throwTo :: (Exception e, MonadIO m) => ThreadId -> e -> m ()

Throw an asynchronous exception to another thread.

Synchronously typed exceptions will be wrapped into an AsyncExceptionWrapper, see https://github.com/fpco/safe-exceptions#determining-sync-vs-async

It's usually a better idea to use the async package, see https://github.com/fpco/safe-exceptions#quickstart

Since: 0.1.0.0

impureThrow :: Exception e => e -> a

Generate a pure value which, when forced, will synchronously throw the given exception

Generally it's better to avoid using this function and instead use throw, see https://github.com/fpco/safe-exceptions#quickstart

Since: 0.1.0.0

fromEither :: (Exception e, MonadIO m) => Either e a -> m a

Unwrap an Either value, throwing its Left value as a runtime exception via throwIO if present.

Since: 0.1.0.0

fromEitherIO :: (Exception e, MonadIO m) => IO (Either e a) -> m a

Same as fromEither, but works on an IO-wrapped Either.

Since: 0.1.0.0

fromEitherM :: (Exception e, MonadIO m) => m (Either e a) -> m a

Same as fromEither, but works on an m-wrapped Either.

Since: 0.1.0.0

Catching (with recovery)

catch :: (MonadUnliftIO m, Exception e) => m a -> (e -> m a) -> m a

Unlifted catch, but will not catch asynchronous exceptions

Since: 0.1.0.0

catchIO :: MonadUnliftIO m => m a -> (IOException -> m a) -> m a

catch specialized to only catching IOExceptions

Since: 0.1.0.0

catchAny :: MonadUnliftIO m => m a -> (SomeException -> m a) -> m a

catch specialized to catch all synchronous exception

Since: 0.1.0.0

catchDeep :: (MonadUnliftIO m, Exception e, NFData a) => m a -> (e -> m a) -> m a

Same as catch, but fully force evaluation of the result value to find all impure exceptions.

Since: 0.1.0.0

catchAnyDeep :: (NFData a, MonadUnliftIO m) => m a -> (SomeException -> m a) -> m a

catchDeep specialized to catch all synchronous exception

Since: 0.1.1.0

catchJust :: (MonadUnliftIO m, Exception e) => (e -> Maybe b) -> m a -> (b -> m a) -> m a

catchJust is like catch but it takes an extra argument which is an exception predicate, a function which selects which type of exceptions we're interested in.

Since: 0.1.0.0

handle :: (MonadUnliftIO m, Exception e) => (e -> m a) -> m a -> m a

Flipped version of catch

Since: 0.1.0.0

handleIO :: MonadUnliftIO m => (IOException -> m a) -> m a -> m a

handle specialized to only catching IOExceptions

Since: 0.1.0.0

handleAny :: MonadUnliftIO m => (SomeException -> m a) -> m a -> m a

Flipped version of catchAny

Since: 0.1.0.0

handleDeep :: (MonadUnliftIO m, Exception e, NFData a) => (e -> m a) -> m a -> m a

Flipped version of catchDeep

Since: 0.1.1.0

handleAnyDeep :: (MonadUnliftIO m, NFData a) => (SomeException -> m a) -> m a -> m a

Flipped version of catchAnyDeep

Since: 0.1.0.0

handleJust :: (MonadUnliftIO m, Exception e) => (e -> Maybe b) -> (b -> m a) -> m a -> m a

Flipped catchJust.

Since: 0.1.0.0

try :: (MonadUnliftIO m, Exception e) => m a -> m (Either e a)

Unlifted try, but will not catch asynchronous exceptions

Since: 0.1.0.0

tryIO :: MonadUnliftIO m => m a -> m (Either IOException a)

try specialized to only catching IOExceptions

Since: 0.1.0.0

tryAny :: MonadUnliftIO m => m a -> m (Either SomeException a)

try specialized to catch all synchronous exceptions

Since: 0.1.0.0

tryDeep :: (MonadUnliftIO m, Exception e, NFData a) => m a -> m (Either e a)

Same as try, but fully force evaluation of the result value to find all impure exceptions.

Since: 0.1.0.0

tryAnyDeep :: (MonadUnliftIO m, NFData a) => m a -> m (Either SomeException a)

tryDeep specialized to catch all synchronous exceptions

Since: 0.1.1.0

tryJust :: (MonadUnliftIO m, Exception e) => (e -> Maybe b) -> m a -> m (Either b a)

A variant of try that takes an exception predicate to select which exceptions are caught.

Since: 0.1.0.0

data Handler m a

Generalized version of Handler

Since: 0.1.0.0

Constructors

Exception e => Handler (e -> m a)

catches :: MonadUnliftIO m => m a -> [Handler m a] -> m a

Same as upstream catches, but will not catch asynchronous exceptions

Since: 0.1.0.0

catchesDeep :: (MonadUnliftIO m, NFData a) => m a -> [Handler m a] -> m a

Same as catches, but fully force evaluation of the result value to find all impure exceptions.

Since: 0.1.0.0

Cleanup (no recovery)

onException :: MonadUnliftIO m => m a -> m b -> m a

Async safe version of onException

Since: 0.1.0.0

bracket :: MonadUnliftIO m => m a -> (a -> m b) -> (a -> m c) -> m c

Async safe version of bracket

Since: 0.1.0.0

bracket_ :: MonadUnliftIO m => m a -> m b -> m c -> m c

Async safe version of bracket_

Since: 0.1.0.0

finally :: MonadUnliftIO m => m a -> m b -> m a

Async safe version of finally

Since: 0.1.0.0

withException :: (MonadUnliftIO m, Exception e) => m a -> (e -> m b) -> m a

Like onException, but provides the handler the thrown exception.

Since: 0.1.0.0

bracketOnError :: MonadUnliftIO m => m a -> (a -> m b) -> (a -> m c) -> m c

Async safe version of bracketOnError

Since: 0.1.0.0

bracketOnError_ :: MonadUnliftIO m => m a -> m b -> m c -> m c

A variant of bracketOnError where the return value from the first computation is not required.

Since: 0.1.0.0

Coercion to sync and async

data SyncExceptionWrapper

Wrap up an asynchronous exception to be treated as a synchronous exception

This is intended to be created via toSyncException

Since: 0.1.0.0

Constructors

Exception e => SyncExceptionWrapper e

Instances

Show SyncExceptionWrapper

Methods

showsPrec :: Int -> SyncExceptionWrapper -> ShowS

show :: SyncExceptionWrapper -> String

showList :: [SyncExceptionWrapper] -> ShowS

Exception SyncExceptionWrapper

Methods

toException :: SyncExceptionWrapper -> SomeException

fromException :: SomeException -> Maybe SyncExceptionWrapper

displayException :: SyncExceptionWrapper -> String

toSyncException :: Exception e => e -> SomeException

Convert an exception into a synchronous exception

For synchronous exceptions, this is the same as toException. For asynchronous exceptions, this will wrap up the exception with SyncExceptionWrapper

Since: 0.1.0.0

data AsyncExceptionWrapper

Wrap up a synchronous exception to be treated as an asynchronous exception

This is intended to be created via toAsyncException

Since: 0.1.0.0

Constructors

Exception e => AsyncExceptionWrapper e

Instances

Show AsyncExceptionWrapper

Methods

showsPrec :: Int -> AsyncExceptionWrapper -> ShowS

show :: AsyncExceptionWrapper -> String

showList :: [AsyncExceptionWrapper] -> ShowS

Exception AsyncExceptionWrapper

Methods

toException :: AsyncExceptionWrapper -> SomeException

fromException :: SomeException -> Maybe AsyncExceptionWrapper

displayException :: AsyncExceptionWrapper -> String

toAsyncException :: Exception e => e -> SomeException

Convert an exception into an asynchronous exception

For asynchronous exceptions, this is the same as toException. For synchronous exceptions, this will wrap up the exception with AsyncExceptionWrapper

Since: 0.1.0.0

Check exception type

isSyncException :: Exception e => e -> Bool

Check if the given exception is synchronous

Since: 0.1.0.0

isAsyncException :: Exception e => e -> Bool

Check if the given exception is asynchronous

Since: 0.1.0.0

Masking

mask :: MonadUnliftIO m => ((forall a. m a -> m a) -> m b) -> m b

Unlifted version of mask

Since: 0.1.0.0

uninterruptibleMask :: MonadUnliftIO m => ((forall a. m a -> m a) -> m b) -> m b

Unlifted version of uninterruptibleMask

Since: 0.1.0.0

mask_ :: MonadUnliftIO m => m a -> m a

Unlifted version of mask_

Since: 0.1.0.0

uninterruptibleMask_ :: MonadUnliftIO m => m a -> m a

Unlifted version of uninterruptibleMask_

Since: 0.1.0.0

Evaluation

evaluate :: MonadIO m => a -> m a

Lifted version of evaluate

evaluateDeep :: (MonadIO m, NFData a) => a -> m a

Deeply evaluate a value using evaluate and NFData.

Since: 0.1.0.0

Reexports

class (Typeable * e, Show e) => Exception e where

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, Typeable)

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
    deriving Typeable

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
    deriving Typeable

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 (Typeable, 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

Methods

toException :: e -> SomeException

fromException :: SomeException -> Maybe e

displayException :: e -> String

Render this exception value in a human-friendly manner.

Default implementation: show.

Since: 4.8.0.0

Instances

Exception Timeout

Methods

toException :: Timeout -> SomeException

fromException :: SomeException -> Maybe Timeout

displayException :: Timeout -> String

Exception Void

Methods

toException :: Void -> SomeException

fromException :: SomeException -> Maybe Void

displayException :: Void -> String

Exception PatternMatchFail

Methods

toException :: PatternMatchFail -> SomeException

fromException :: SomeException -> Maybe PatternMatchFail

displayException :: PatternMatchFail -> String

Exception RecSelError

Methods

toException :: RecSelError -> SomeException

fromException :: SomeException -> Maybe RecSelError

displayException :: RecSelError -> String

Exception RecConError

Methods

toException :: RecConError -> SomeException

fromException :: SomeException -> Maybe RecConError

displayException :: RecConError -> String

Exception RecUpdError

Methods

toException :: RecUpdError -> SomeException

fromException :: SomeException -> Maybe RecUpdError

displayException :: RecUpdError -> String

Exception NoMethodError

Methods

toException :: NoMethodError -> SomeException

fromException :: SomeException -> Maybe NoMethodError

displayException :: NoMethodError -> String

Exception TypeError

Methods

toException :: TypeError -> SomeException

fromException :: SomeException -> Maybe TypeError

displayException :: TypeError -> String

Exception NonTermination

Methods

toException :: NonTermination -> SomeException

fromException :: SomeException -> Maybe NonTermination

displayException :: NonTermination -> String

Exception NestedAtomically

Methods

toException :: NestedAtomically -> SomeException

fromException :: SomeException -> Maybe NestedAtomically

displayException :: NestedAtomically -> String

Exception BlockedIndefinitelyOnMVar

Methods

toException :: BlockedIndefinitelyOnMVar -> SomeException

fromException :: SomeException -> Maybe BlockedIndefinitelyOnMVar

displayException :: BlockedIndefinitelyOnMVar -> String

Exception BlockedIndefinitelyOnSTM

Methods

toException :: BlockedIndefinitelyOnSTM -> SomeException

fromException :: SomeException -> Maybe BlockedIndefinitelyOnSTM

displayException :: BlockedIndefinitelyOnSTM -> String

Exception Deadlock

Methods

toException :: Deadlock -> SomeException

fromException :: SomeException -> Maybe Deadlock

displayException :: Deadlock -> String

Exception AllocationLimitExceeded

Methods

toException :: AllocationLimitExceeded -> SomeException

fromException :: SomeException -> Maybe AllocationLimitExceeded

displayException :: AllocationLimitExceeded -> String

Exception AssertionFailed

Methods

toException :: AssertionFailed -> SomeException

fromException :: SomeException -> Maybe AssertionFailed

displayException :: AssertionFailed -> String

Exception SomeAsyncException

Methods

toException :: SomeAsyncException -> SomeException

fromException :: SomeException -> Maybe SomeAsyncException

displayException :: SomeAsyncException -> String

Exception AsyncException

Methods

toException :: AsyncException -> SomeException

fromException :: SomeException -> Maybe AsyncException

displayException :: AsyncException -> String

Exception ArrayException

Methods

toException :: ArrayException -> SomeException

fromException :: SomeException -> Maybe ArrayException

displayException :: ArrayException -> String

Exception ExitCode

Methods

toException :: ExitCode -> SomeException

fromException :: SomeException -> Maybe ExitCode

displayException :: ExitCode -> String

Exception IOException

Methods

toException :: IOException -> SomeException

fromException :: SomeException -> Maybe IOException

displayException :: IOException -> String

Exception ErrorCall

Methods

toException :: ErrorCall -> SomeException

fromException :: SomeException -> Maybe ErrorCall

displayException :: ErrorCall -> String

Exception ArithException

Methods

toException :: ArithException -> SomeException

fromException :: SomeException -> Maybe ArithException

displayException :: ArithException -> String

Exception SomeException

Methods

toException :: SomeException -> SomeException

fromException :: SomeException -> Maybe SomeException

displayException :: SomeException -> String

Exception InvalidAccess

Methods

toException :: InvalidAccess -> SomeException

fromException :: SomeException -> Maybe InvalidAccess

displayException :: InvalidAccess -> String

Exception StringException

Methods

toException :: StringException -> SomeException

fromException :: SomeException -> Maybe StringException

displayException :: StringException -> String

Exception AsyncExceptionWrapper

Methods

toException :: AsyncExceptionWrapper -> SomeException

fromException :: SomeException -> Maybe AsyncExceptionWrapper

displayException :: AsyncExceptionWrapper -> String

Exception SyncExceptionWrapper

Methods

toException :: SyncExceptionWrapper -> SomeException

fromException :: SomeException -> Maybe SyncExceptionWrapper

displayException :: SyncExceptionWrapper -> String

class Typeable k a

The class Typeable allows a concrete representation of a type to be calculated.

Minimal complete definition

typeRep#

data SomeException :: * where

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.

Constructors

SomeException :: SomeException

Instances

Show SomeException

Methods

showsPrec :: Int -> SomeException -> ShowS

show :: SomeException -> String

showList :: [SomeException] -> ShowS

Exception SomeException

Methods

toException :: SomeException -> SomeException

fromException :: SomeException -> Maybe SomeException

displayException :: SomeException -> String

data SomeAsyncException :: * where

Superclass for asynchronous exceptions.

Since: 4.7.0.0

Constructors

SomeAsyncException :: SomeAsyncException

Instances

Show SomeAsyncException

Methods

showsPrec :: Int -> SomeAsyncException -> ShowS

show :: SomeAsyncException -> String

showList :: [SomeAsyncException] -> ShowS

Exception SomeAsyncException

Methods

toException :: SomeAsyncException -> SomeException

fromException :: SomeException -> Maybe SomeAsyncException

displayException :: SomeAsyncException -> String

data IOException :: *

Exceptions that occur in the IO monad. An IOException records a more specific error type, a descriptive string and maybe the handle that was used when the error was flagged.

Instances

Eq IOException

Methods

(==) :: IOException -> IOException -> Bool

(/=) :: IOException -> IOException -> Bool

Show IOException

Methods

showsPrec :: Int -> IOException -> ShowS

show :: IOException -> String

showList :: [IOException] -> ShowS

Exception IOException

Methods

toException :: IOException -> SomeException

fromException :: SomeException -> Maybe IOException

displayException :: IOException -> String

Error IOException

Methods

noMsg :: IOException

strMsg :: String -> IOException

assert :: Bool -> a -> a

If the first argument evaluates to True, then the result is the second argument. Otherwise an AssertionFailed exception is raised, containing a String with the source file and line number of the call to assert.

Assertions can normally be turned on or off with a compiler flag (for GHC, assertions are normally on unless optimisation is turned on with -O or the -fignore-asserts option is given). When assertions are turned off, the first argument to assert is ignored, and the second argument is returned as the result.