Synchronously throw the given exception

Since: 0.1.0.0

Synonym for throw

Since: 0.1.0.0

Synonym for throw

Since: 0.1.0.0

Throw an asynchronous exception to another thread

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

Since: 0.1.0.0

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

Same as upstream catch, but will not catch asynchronous exceptions

Since: 0.1.0.0

catch specialized to only catching IOExceptions

Since: 0.1.3.0

catch specialized to catch all synchronous exception

Since: 0.1.0.0

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

Since: 0.1.1.0

catchDeep specialized to catch all synchronous exception

Since: 0.1.1.0

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

Since: 0.1.0.0

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: 0.1.4.0

Flipped version of catch

Since: 0.1.0.0

handle specialized to only catching IOExceptions

Since: 0.1.3.0

Flipped version of catchAny

Since: 0.1.0.0

Flipped version of catchDeep

Since: 0.1.1.0

Flipped version of catchAnyDeep

Since: 0.1.1.0

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

Since: 0.1.0.0

Flipped catchJust.

Since: 0.1.4.0

Same as upstream try, but will not catch asynchronous exceptions

Since: 0.1.0.0

try specialized to only catching IOExceptions

Since: 0.1.3.0

try specialized to catch all synchronous exceptions

Since: 0.1.0.0

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

Since: 0.1.1.0

tryDeep specialized to catch all synchronous exceptions

Since: 0.1.1.0

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

Since: 0.1.0.0

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

Since: 0.1.4.0

You need this when using catches.

Same as upstream catches, but will not catch asynchronous exceptions

Since: 0.1.2.0

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

Since: 0.1.2.0

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

Since: 0.1.2.0

Async safe version of onException

Since: 0.1.0.0

Async safe version of bracket

Since: 0.1.0.0

Async safe version of bracket_

Since: 0.1.0.0

Async safe version of finally

Since: 0.1.0.0

Like onException, but provides the handler the thrown exception.

Since: 0.1.0.0

Async safe version of bracketOnError

Since: 0.1.0.0

Async safe version of bracketOnError_

Since: 0.1.0.0

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

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

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

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 if the given exception is synchronous

Since: 0.1.0.0

Check if the given exception is asynchronous

Since: 0.1.0.0

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.

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.

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, and stacks such as ErrorT e IO which provide for multiple failure modes, are invalid instances of this class.

Note that this package does provide a MonadMask instance for CatchT. This instance is only valid if the base monad provides no ability to provide multiple exit. For example, IO or Either would be invalid base monads, but Reader or State would be acceptable.

Instances should ensure that, in the following code:

f `finally` g

The action g is called regardless of what occurs within f, including async exceptions.

Like mask, but does not pass a restore action to the argument.

Like uninterruptibleMask, but does not pass a restore action to the argument.

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.

Flipped catchIOError

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

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

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.

Superclass for asynchronous exceptions.

Since: 4.7.0.0

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.