-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/
-- | Safe, consistent, and easy exception handling
--
-- Please see README.md
@package safe-exceptions
@version 0.1.7.4
-- | Please see the README.md file in the safe-exceptions repo for
-- information on how to use this module. Relevant links:
--
--
module Control.Exception.Safe
-- | Synchronously throw the given exception
throw :: () => (MonadThrow m, Exception e) => e -> m a
-- | Synonym for throw
throwIO :: () => (MonadThrow m, Exception e) => e -> m a
-- | Synonym for throw
throwM :: () => (MonadThrow m, Exception e) => e -> 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.
throwString :: (MonadThrow m, HasCallStack) => String -> m a
-- | 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).
data StringException
StringException :: String -> CallStack -> StringException
-- | 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
throwTo :: (Exception e, MonadIO m) => ThreadId -> e -> m ()
-- | 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
impureThrow :: () => Exception e => e -> a
-- | Same as upstream catch, but will not catch asynchronous
-- exceptions
catch :: () => (MonadCatch m, Exception e) => m a -> (e -> m a) -> m a
-- | catch specialized to only catching IOExceptions
catchIO :: () => MonadCatch m => m a -> (IOException -> m a) -> m a
-- | catch specialized to catch all synchronous exception
catchAny :: () => MonadCatch m => m a -> (SomeException -> m a) -> m a
-- | Same as catch, but fully force evaluation of the result value
-- to find all impure exceptions.
catchDeep :: () => (MonadCatch m, MonadIO m, Exception e, NFData a) => m a -> (e -> m a) -> m a
-- | catchDeep specialized to catch all synchronous exception
catchAnyDeep :: () => (MonadCatch m, MonadIO m, NFData a) => m a -> (SomeException -> m a) -> m a
-- | catch without async exception safety
--
-- Generally it's better to avoid using this function since we do not
-- want to recover from async exceptions, see
-- https://github.com/fpco/safe-exceptions#quickstart
catchAsync :: () => (MonadCatch m, Exception e) => m a -> (e -> 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.
catchJust :: () => (MonadCatch m, Exception e) => (e -> Maybe b) -> m a -> (b -> m a) -> m a
-- | Flipped version of catch
handle :: () => (MonadCatch m, Exception e) => (e -> m a) -> m a -> m a
-- | handle specialized to only catching IOExceptions
handleIO :: () => MonadCatch m => (IOException -> m a) -> m a -> m a
-- | Flipped version of catchAny
handleAny :: () => MonadCatch m => (SomeException -> m a) -> m a -> m a
-- | Flipped version of catchDeep
handleDeep :: () => (MonadCatch m, Exception e, MonadIO m, NFData a) => (e -> m a) -> m a -> m a
-- | Flipped version of catchAnyDeep
handleAnyDeep :: () => (MonadCatch m, MonadIO m, NFData a) => (SomeException -> m a) -> m a -> m a
-- | Flipped version of catchAsync
--
-- Generally it's better to avoid using this function since we do not
-- want to recover from async exceptions, see
-- https://github.com/fpco/safe-exceptions#quickstart
handleAsync :: () => (MonadCatch m, Exception e) => (e -> m a) -> m a -> m a
-- | Flipped catchJust.
handleJust :: () => (MonadCatch m, Exception e) => (e -> Maybe b) -> (b -> m a) -> m a -> m a
-- | Same as upstream try, but will not catch asynchronous
-- exceptions
try :: () => (MonadCatch m, Exception e) => m a -> m (Either e a)
-- | try specialized to only catching IOExceptions
tryIO :: () => MonadCatch m => m a -> m (Either IOException a)
-- | try specialized to catch all synchronous exceptions
tryAny :: () => MonadCatch m => m a -> m (Either SomeException a)
-- | Same as try, but fully force evaluation of the result value to
-- find all impure exceptions.
tryDeep :: () => (MonadCatch m, MonadIO m, Exception e, NFData a) => m a -> m (Either e a)
-- | tryDeep specialized to catch all synchronous exceptions
tryAnyDeep :: () => (MonadCatch m, MonadIO m, NFData a) => m a -> m (Either SomeException a)
-- | try without async exception safety
--
-- Generally it's better to avoid using this function since we do not
-- want to recover from async exceptions, see
-- https://github.com/fpco/safe-exceptions#quickstart
tryAsync :: () => (MonadCatch m, Exception e) => m a -> m (Either e a)
-- | A variant of try that takes an exception predicate to select
-- which exceptions are caught.
tryJust :: () => (MonadCatch m, Exception e) => (e -> Maybe b) -> m a -> m (Either b a)
-- | Generalized version of Handler
data Handler (m :: Type -> Type) a
Handler :: (e -> m a) -> Handler (m :: Type -> Type) a
-- | Same as upstream catches, but will not catch asynchronous
-- exceptions
catches :: () => (MonadCatch m, MonadThrow m) => m a -> [Handler m a] -> m a
-- | Same as catches, but fully force evaluation of the result value
-- to find all impure exceptions.
catchesDeep :: () => (MonadCatch m, MonadThrow m, MonadIO m, NFData a) => m a -> [Handler m a] -> m a
-- | catches without async exception safety
--
-- Generally it's better to avoid using this function since we do not
-- want to recover from async exceptions, see
-- https://github.com/fpco/safe-exceptions#quickstart
catchesAsync :: () => (MonadCatch m, MonadThrow m) => m a -> [Handler m a] -> m a
-- | Async safe version of onException
onException :: () => MonadMask m => m a -> m b -> m a
-- | Async safe version of bracket
bracket :: forall m a b c. () => MonadMask m => m a -> (a -> m b) -> (a -> m c) -> m c
-- | Async safe version of bracket_
bracket_ :: () => MonadMask m => m a -> m b -> m c -> m c
-- | Async safe version of finally
finally :: () => MonadMask m => m a -> m b -> m a
-- | Like onException, but provides the handler the thrown
-- exception.
withException :: () => (MonadMask m, Exception e) => m a -> (e -> m b) -> m a
-- | Async safe version of bracketOnError
bracketOnError :: forall m a b c. () => MonadMask m => m a -> (a -> m b) -> (a -> m c) -> m c
-- | A variant of bracketOnError where the return value from the
-- first computation is not required.
bracketOnError_ :: () => MonadMask m => m a -> m b -> m c -> m c
-- | Async safe version of bracket with access to the exception in
-- the cleanup action.
bracketWithError :: forall m a b c. () => MonadMask m => m a -> (Maybe SomeException -> a -> m b) -> (a -> m c) -> m c
-- | Wrap up an asynchronous exception to be treated as a synchronous
-- exception
--
-- This is intended to be created via toSyncException
data SyncExceptionWrapper
SyncExceptionWrapper :: e -> SyncExceptionWrapper
-- | 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
toSyncException :: Exception e => e -> SomeException
-- | Wrap up a synchronous exception to be treated as an asynchronous
-- exception
--
-- This is intended to be created via toAsyncException
data AsyncExceptionWrapper
AsyncExceptionWrapper :: e -> AsyncExceptionWrapper
-- | 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
toAsyncException :: Exception e => e -> SomeException
-- | Check if the given exception is synchronous
isSyncException :: Exception e => e -> Bool
-- | Check if the given exception is asynchronous
isAsyncException :: Exception e => e -> Bool
-- | A class for monads in which exceptions may be thrown.
--
-- Instances should obey the following law:
--
--
-- throwM e >> x = throwM e
--
--
-- In other words, throwing an exception short-circuits the rest of the
-- monadic computation.
class Monad m => MonadThrow (m :: Type -> Type)
-- | A class for monads which allow exceptions to be caught, in particular
-- exceptions which were thrown by throwM.
--
-- Instances should obey the following law:
--
--
-- catch (throwM e) f = f e
--
--
-- Note that the ability to catch an exception does not guarantee
-- that we can deal with all possible exit points from a computation.
-- Some monads, such as continuation-based stacks, allow for more than
-- just a success/failure strategy, and therefore catch
-- cannot be used by those monads to properly implement a function
-- such as finally. For more information, see MonadMask.
class MonadThrow m => MonadCatch (m :: Type -> Type)
-- | A class for monads which provide for the ability to account for all
-- possible exit points from a computation, and to mask asynchronous
-- exceptions. Continuation-based monads are invalid instances of this
-- class.
--
-- Instances should ensure that, in the following code:
--
--
-- fg = f `finally` g
--
--
-- The action g is called regardless of what occurs within
-- f, including async exceptions. Some monads allow f
-- to abort the computation via other effects than throwing an exception.
-- For simplicity, we will consider aborting and throwing an exception to
-- be two forms of "throwing an error".
--
-- If f and g both throw an error, the error thrown by
-- fg depends on which errors we're talking about. In a monad
-- transformer stack, the deeper layers override the effects of the inner
-- layers; for example, ExceptT e1 (Except e2) a represents a
-- value of type Either e2 (Either e1 a), so throwing both an
-- e1 and an e2 will result in Left e2. If
-- f and g both throw an error from the same layer,
-- instances should ensure that the error from g wins.
--
-- Effects other than throwing an error are also overriden by the deeper
-- layers. For example, StateT s Maybe a represents a value of
-- type s -> Maybe (a, s), so if an error thrown from
-- f causes this function to return Nothing, any
-- changes to the state which f also performed will be erased.
-- As a result, g will see the state as it was before
-- f. Once g completes, f's error will be
-- rethrown, so g' state changes will be erased as well. This is
-- the normal interaction between effects in a monad transformer stack.
--
-- By contrast, lifted-base's version of finally always
-- discards all of g's non-IO effects, and g never sees
-- any of f's non-IO effects, regardless of the layer ordering
-- and regardless of whether f throws an error. This is not the
-- result of interacting effects, but a consequence of
-- MonadBaseControl's approach.
class MonadCatch m => MonadMask (m :: Type -> Type)
-- | Runs an action with asynchronous exceptions disabled. The action is
-- provided a method for restoring the async. environment to what it was
-- at the mask call. See Control.Exception's mask.
mask :: MonadMask m => ((forall a. () => m a -> m a) -> m b) -> m b
-- | Like mask, but the masked computation is not interruptible (see
-- Control.Exception's uninterruptibleMask. WARNING: Only
-- use if you need to mask exceptions around an interruptible operation
-- AND you can guarantee the interruptible operation will only block for
-- a short period of time. Otherwise you render the program/thread
-- unresponsive and/or unkillable.
uninterruptibleMask :: MonadMask m => ((forall a. () => m a -> m a) -> m b) -> m b
-- | A generalized version of bracket which uses ExitCase to
-- distinguish the different exit cases, and returns the values of both
-- the use and release actions. In practice, this extra
-- information is rarely needed, so it is often more convenient to use
-- one of the simpler functions which are defined in terms of this one,
-- such as bracket, finally, onError, and
-- bracketOnError.
--
-- This function exists because in order to thread their effects through
-- the execution of bracket, monad transformers need values to be
-- threaded from use to release and from
-- release to the output value.
--
-- NOTE This method was added in version 0.9.0 of this library.
-- Previously, implementation of functions like bracket and
-- finally in this module were based on the mask and
-- uninterruptibleMask functions only, disallowing some classes of
-- tranformers from having MonadMask instances (notably
-- multi-exit-point transformers like ExceptT). If you are a
-- library author, you'll now need to provide an implementation for this
-- method. The StateT implementation demonstrates most of the
-- subtleties:
--
--
-- generalBracket acquire release use = StateT $ s0 -> do
-- ((b, _s2), (c, s3)) <- generalBracket
-- (runStateT acquire s0)
-- ((resource, s1) exitCase -> case exitCase of
-- ExitCaseSuccess (b, s2) -> runStateT (release resource (ExitCaseSuccess b)) s2
--
-- -- In the two other cases, the base monad overrides use's state
-- -- changes and the state reverts to s1.
-- ExitCaseException e -> runStateT (release resource (ExitCaseException e)) s1
-- ExitCaseAbort -> runStateT (release resource ExitCaseAbort) s1
-- )
-- ((resource, s1) -> runStateT (use resource) s1)
-- return ((b, c), s3)
--
--
-- The StateT s m implementation of generalBracket
-- delegates to the m implementation of generalBracket.
-- The acquire, use, and release arguments
-- given to StateT's implementation produce actions of type
-- StateT s m a, StateT s m b, and StateT s m
-- c. In order to run those actions in the base monad, we need to
-- call runStateT, from which we obtain actions of type m
-- (a, s), m (b, s), and m (c, s). Since each
-- action produces the next state, it is important to feed the state
-- produced by the previous action to the next action.
--
-- In the ExitCaseSuccess case, the state starts at s0,
-- flows through acquire to become s1, flows through
-- use to become s2, and finally flows through
-- release to become s3. In the other two cases,
-- release does not receive the value s2, so its action
-- cannot see the state changes performed by use. This is fine,
-- because in those two cases, an error was thrown in the base monad, so
-- as per the usual interaction between effects in a monad transformer
-- stack, those state changes get reverted. So we start from s1
-- instead.
--
-- Finally, the m implementation of generalBracket
-- returns the pairs (b, s) and (c, s). For monad
-- transformers other than StateT, this will be some other type
-- representing the effects and values performed and returned by the
-- use and release actions. The effect part of the
-- use result, in this case _s2, usually needs to be
-- discarded, since those effects have already been incorporated in the
-- release action.
--
-- The only effect which is intentionally not incorporated in the
-- release action is the effect of throwing an error. In that
-- case, the error must be re-thrown. One subtlety which is easy to miss
-- is that in the case in which use and release both
-- throw an error, the error from release should take priority.
-- Here is an implementation for ExceptT which demonstrates how
-- to do this.
--
--
-- generalBracket acquire release use = ExceptT $ do
-- (eb, ec) <- generalBracket
-- (runExceptT acquire)
-- (eresource exitCase -> case eresource of
-- Left e -> return (Left e) -- nothing to release, acquire didn't succeed
-- Right resource -> case exitCase of
-- ExitCaseSuccess (Right b) -> runExceptT (release resource (ExitCaseSuccess b))
-- ExitCaseException e -> runExceptT (release resource (ExitCaseException e))
-- _ -> runExceptT (release resource ExitCaseAbort))
-- (either (return . Left) (runExceptT . use))
-- return $ do
-- -- The order in which we perform those two Either effects determines
-- -- which error will win if they are both Lefts. We want the error from
-- -- release to win.
-- c <- ec
-- b <- eb
-- return (b, c)
--
generalBracket :: MonadMask m => m a -> (a -> ExitCase b -> m c) -> (a -> m b) -> m (b, c)
-- | Like mask, but does not pass a restore action to the
-- argument.
mask_ :: MonadMask m => m a -> m a
-- | Like uninterruptibleMask, but does not pass a restore
-- action to the argument.
uninterruptibleMask_ :: MonadMask m => m a -> m a
-- | Catch all IOError (eqv. IOException) exceptions. Still
-- somewhat too general, but better than using catchAll. See
-- catchIf for an easy way of catching specific IOErrors
-- based on the predicates in System.IO.Error.
catchIOError :: MonadCatch m => m a -> (IOError -> m a) -> m a
-- | Flipped catchIOError
handleIOError :: MonadCatch m => (IOError -> m a) -> m a -> m a
-- | 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
--
class (Typeable e, Show e) => Exception e
toException :: Exception e => e -> SomeException
fromException :: Exception e => SomeException -> Maybe e
-- | Render this exception value in a human-friendly manner.
--
-- Default implementation: show.
displayException :: Exception e => e -> String
-- | The class Typeable allows a concrete representation of a type
-- to be calculated.
class Typeable (a :: k)
-- | 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.
data SomeException
SomeException :: e -> SomeException
-- | Superclass for asynchronous exceptions.
data SomeAsyncException
SomeAsyncException :: e -> SomeAsyncException
-- | 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.
data IOException
-- | 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.
assert :: Bool -> a -> a
instance GHC.Show.Show Control.Exception.Safe.AsyncExceptionWrapper
instance GHC.Exception.Type.Exception Control.Exception.Safe.AsyncExceptionWrapper
instance GHC.Show.Show Control.Exception.Safe.SyncExceptionWrapper
instance GHC.Exception.Type.Exception Control.Exception.Safe.SyncExceptionWrapper
instance GHC.Show.Show Control.Exception.Safe.StringException
instance GHC.Exception.Type.Exception Control.Exception.Safe.StringException