lifted-base-0.2.3.12: lifted IO operations from the base library

CopyrightBas van Dijk Anders Kaseorg
LicenseBSD-style
MaintainerBas van Dijk <v.dijk.bas@gmail.com>
Stabilityexperimental
Portabilitynon-portable (extended exceptions)
Safe HaskellSafe
LanguageHaskell98

Control.Exception.Lifted

Contents

Description

This is a wrapped version of Control.Exception with types generalized from IO to all monads in either MonadBase or MonadBaseControl.

Synopsis

Documentation

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.

mapException :: (Exception e1, Exception e2) => (e1 -> e2) -> a -> a #

This function maps one exception into another as proposed in the paper "A semantics for imprecise exceptions".

newtype PatternMatchFail #

A pattern match failed. The String gives information about the source location of the pattern.

Constructors

PatternMatchFail String 

newtype RecSelError #

A record selector was applied to a constructor without the appropriate field. This can only happen with a datatype with multiple constructors, where some fields are in one constructor but not another. The String gives information about the source location of the record selector.

Constructors

RecSelError String 

newtype RecConError #

An uninitialised record field was used. The String gives information about the source location where the record was constructed.

Constructors

RecConError String 

newtype RecUpdError #

A record update was performed on a constructor without the appropriate field. This can only happen with a datatype with multiple constructors, where some fields are in one constructor but not another. The String gives information about the source location of the record update.

Constructors

RecUpdError String 

newtype NoMethodError #

A class method without a definition (neither a default definition, nor a definition in the appropriate instance) was called. The String gives information about which method it was.

Constructors

NoMethodError String 

newtype TypeError #

An expression that didn't typecheck during compile time was called. This is only possible with -fdefer-type-errors. The String gives details about the failed type check.

Since: base-4.9.0.0

Constructors

TypeError String 
Instances
Show TypeError

Since: base-4.9.0.0

Instance details

Defined in Control.Exception.Base

Exception TypeError

Since: base-4.9.0.0

Instance details

Defined in Control.Exception.Base

data NonTermination #

Thrown when the runtime system detects that the computation is guaranteed not to terminate. Note that there is no guarantee that the runtime system will notice whether any given computation is guaranteed to terminate or not.

Constructors

NonTermination 

data NestedAtomically #

Thrown when the program attempts to call atomically, from the stm package, inside another call to atomically.

Constructors

NestedAtomically 

asyncExceptionToException :: Exception e => e -> SomeException #

Since: base-4.7.0.0

data BlockedIndefinitelyOnMVar #

The thread is blocked on an MVar, but there are no other references to the MVar so it can't ever continue.

data BlockedIndefinitelyOnSTM #

The thread is waiting to retry an STM transaction, but there are no other references to any TVars involved, so it can't ever continue.

data Deadlock #

There are no runnable threads, so the program is deadlocked. The Deadlock exception is raised in the main thread only.

Constructors

Deadlock 
Instances
Show Deadlock

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception Deadlock

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

newtype CompactionFailed #

Compaction found an object that cannot be compacted. Functions cannot be compacted, nor can mutable objects or pinned objects. See compact.

Since: base-4.10.0.0

Constructors

CompactionFailed String 

data SomeAsyncException where #

Superclass for asynchronous exceptions.

Since: base-4.7.0.0

Constructors

SomeAsyncException :: forall e. Exception e => e -> SomeAsyncException 

data AsyncException #

Asynchronous exceptions.

Constructors

StackOverflow

The current thread's stack exceeded its limit. Since an exception has been raised, the thread's stack will certainly be below its limit again, but the programmer should take remedial action immediately.

HeapOverflow

The program's heap is reaching its limit, and the program should take action to reduce the amount of live data it has. Notes:

  • It is undefined which thread receives this exception. GHC currently throws this to the same thread that receives UserInterrupt, but this may change in the future.
  • The GHC RTS currently can only recover from heap overflow if it detects that an explicit memory limit (set via RTS flags). has been exceeded. Currently, failure to allocate memory from the operating system results in immediate termination of the program.
ThreadKilled

This exception is raised by another thread calling killThread, or by the system if it needs to terminate the thread for some reason.

UserInterrupt

This exception is raised by default in the main thread of the program when the user requests to terminate the program via the usual mechanism(s) (e.g. Control-C in the console).

data ArrayException #

Exceptions generated by array operations

Constructors

IndexOutOfBounds String

An attempt was made to index an array outside its declared bounds.

UndefinedElement String

An attempt was made to evaluate an element of an array that had not been initialized.

interruptible :: IO a -> IO a #

Allow asynchronous exceptions to be raised even inside mask, making the operation interruptible (see the discussion of "Interruptible operations" in Exception).

When called outside mask, or inside uninterruptibleMask, this function has no effect.

Since: base-4.9.0.0

data MaskingState #

Describes the behaviour of a thread when an asynchronous exception is received.

Constructors

Unmasked

asynchronous exceptions are unmasked (the normal state)

MaskedInterruptible

the state during mask: asynchronous exceptions are masked, but blocking operations may still be interrupted

MaskedUninterruptible

the state during uninterruptibleMask: asynchronous exceptions are masked, and blocking operations may not be interrupted

Instances
Eq MaskingState

Since: base-4.3.0.0

Instance details

Defined in GHC.IO

Show MaskingState

Since: base-4.3.0.0

Instance details

Defined in GHC.IO

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

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Show IOException

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception IOException

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Error IOException 
Instance details

Defined in Control.Monad.Trans.Error

throw :: Exception e => e -> a #

Throw an exception. Exceptions may be thrown from purely functional code, but may only be caught within the IO monad.

data ErrorCall #

This is thrown when the user calls error. The first String is the argument given to error, second String is the location.

Bundled Patterns

pattern ErrorCall :: String -> ErrorCall 
Instances
Eq ErrorCall

Since: base-4.7.0.0

Instance details

Defined in GHC.Exception

Ord ErrorCall

Since: base-4.7.0.0

Instance details

Defined in GHC.Exception

Show ErrorCall

Since: base-4.0.0.0

Instance details

Defined in GHC.Exception

Exception ErrorCall

Since: base-4.0.0.0

Instance details

Defined in GHC.Exception

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

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

Minimal complete definition

Nothing

Methods

toException :: e -> SomeException #

fromException :: SomeException -> Maybe e #

displayException :: e -> String #

Render this exception value in a human-friendly manner.

Default implementation: show.

Since: base-4.8.0.0

Instances
Exception PatternMatchFail

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception RecSelError

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception RecConError

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception RecUpdError

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception NoMethodError

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception TypeError

Since: base-4.9.0.0

Instance details

Defined in Control.Exception.Base

Exception NonTermination

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception NestedAtomically

Since: base-4.0

Instance details

Defined in Control.Exception.Base

Exception BlockedIndefinitelyOnMVar

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception BlockedIndefinitelyOnSTM

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception Deadlock

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception AllocationLimitExceeded

Since: base-4.8.0.0

Instance details

Defined in GHC.IO.Exception

Exception CompactionFailed

Since: base-4.10.0.0

Instance details

Defined in GHC.IO.Exception

Exception AssertionFailed

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception SomeAsyncException

Since: base-4.7.0.0

Instance details

Defined in GHC.IO.Exception

Exception AsyncException

Since: base-4.7.0.0

Instance details

Defined in GHC.IO.Exception

Exception ArrayException

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception FixIOException

Since: base-4.11.0.0

Instance details

Defined in GHC.IO.Exception

Exception ExitCode

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception IOException

Since: base-4.1.0.0

Instance details

Defined in GHC.IO.Exception

Exception ErrorCall

Since: base-4.0.0.0

Instance details

Defined in GHC.Exception

Exception ArithException

Since: base-4.0.0.0

Instance details

Defined in GHC.Exception.Type

Exception SomeException

Since: base-3.0

Instance details

Defined in GHC.Exception.Type

Exception Timeout

Since: base-4.7.0.0

Instance details

Defined in System.Timeout

Methods

toException :: Timeout -> SomeException #

fromException :: SomeException -> Maybe Timeout #

displayException :: Timeout -> String #

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 :: forall e. Exception e => e -> SomeException 

Throwing exceptions

throwIO :: (MonadBase IO m, Exception e) => e -> m a #

Generalized version of throwIO.

ioError :: MonadBase IO m => IOError -> m a #

Generalized version of ioError.

throwTo :: (MonadBase IO m, Exception e) => ThreadId -> e -> m () #

Generalized version of throwTo.

Catching exceptions

The catch functions

catch #

Arguments

:: (MonadBaseControl IO m, Exception e) 
=> m a

The computation to run

-> (e -> m a)

Handler to invoke if an exception is raised

-> m a 

Generalized version of catch.

Note, when the given computation throws an exception any monadic side effects in m will be discarded.

catches :: MonadBaseControl IO m => m a -> [Handler m a] -> m a #

Generalized version of catches.

Note, when the given computation throws an exception any monadic side effects in m will be discarded.

data Handler m a #

Generalized version of Handler.

Constructors

Exception e => Handler (e -> m a) 

catchJust #

Arguments

:: (MonadBaseControl IO m, Exception e) 
=> (e -> Maybe b)

Predicate to select exceptions

-> m a

Computation to run

-> (b -> m a)

Handler

-> m a 

Generalized version of catchJust.

Note, when the given computation throws an exception any monadic side effects in m will be discarded.

The handle functions

handle :: (MonadBaseControl IO m, Exception e) => (e -> m a) -> m a -> m a #

Generalized version of handle.

Note, when the given computation throws an exception any monadic side effects in m will be discarded.

handleJust :: (MonadBaseControl IO m, Exception e) => (e -> Maybe b) -> (b -> m a) -> m a -> m a #

Generalized version of handleJust.

Note, when the given computation throws an exception any monadic side effects in m will be discarded.

The try functions

try :: (MonadBaseControl IO m, Exception e) => m a -> m (Either e a) #

Generalized version of try.

Note, when the given computation throws an exception any monadic side effects in m will be discarded.

tryJust :: (MonadBaseControl IO m, Exception e) => (e -> Maybe b) -> m a -> m (Either b a) #

Generalized version of tryJust.

Note, when the given computation throws an exception any monadic side effects in m will be discarded.

The evaluate function

evaluate :: MonadBase IO m => a -> m a #

Generalized version of evaluate.

Asynchronous Exceptions

Asynchronous exception control

The following functions allow a thread to control delivery of asynchronous exceptions during a critical region.

mask :: MonadBaseControl IO m => ((forall a. m a -> m a) -> m b) -> m b #

Generalized version of mask.

mask_ :: MonadBaseControl IO m => m a -> m a #

Generalized version of mask_.

uninterruptibleMask :: MonadBaseControl IO m => ((forall a. m a -> m a) -> m b) -> m b #

Generalized version of uninterruptibleMask.

uninterruptibleMask_ :: MonadBaseControl IO m => m a -> m a #

Generalized version of uninterruptibleMask_.

getMaskingState :: MonadBase IO m => m MaskingState #

Generalized version of getMaskingState.

allowInterrupt :: MonadBase IO m => m () #

Generalized version of allowInterrupt.

Brackets

bracket #

Arguments

:: MonadBaseControl IO m 
=> m a

computation to run first ("acquire resource")

-> (a -> m b)

computation to run last ("release resource")

-> (a -> m c)

computation to run in-between

-> m c 

Generalized version of bracket.

Note:

  • When the "acquire" or "release" computations throw exceptions any monadic side effects in m will be discarded.
  • When the "in-between" computation throws an exception any monadic side effects in m produced by that computation will be discarded but the side effects of the "acquire" or "release" computations will be retained.
  • Also, any monadic side effects in m of the "release" computation will be discarded; it is run only for its side effects in IO.

Note that when your acquire and release computations are of type IO it will be more efficient to write:

liftBaseOp (bracket acquire release)

bracket_ #

Arguments

:: MonadBaseControl IO m 
=> m a

computation to run first ("acquire resource")

-> m b

computation to run last ("release resource")

-> m c

computation to run in-between

-> m c 

Generalized version of bracket_.

Note any monadic side effects in m of both the "acquire" and "release" computations will be discarded. To keep the monadic side effects of the "acquire" computation, use bracket with constant functions instead.

Note that when your acquire and release computations are of type IO it will be more efficient to write:

liftBaseOp_ (bracket_ acquire release)

bracketOnError #

Arguments

:: MonadBaseControl IO m 
=> m a

computation to run first ("acquire resource")

-> (a -> m b)

computation to run last ("release resource")

-> (a -> m c)

computation to run in-between

-> m c 

Generalized version of bracketOnError.

Note:

  • When the "acquire" or "release" computations throw exceptions any monadic side effects in m will be discarded.
  • When the "in-between" computation throws an exception any monadic side effects in m produced by that computation will be discarded but the side effects of the "acquire" computation will be retained.
  • Also, any monadic side effects in m of the "release" computation will be discarded; it is run only for its side effects in IO.

Note that when your acquire and release computations are of type IO it will be more efficient to write:

liftBaseOp (bracketOnError acquire release)

Utilities

finally #

Arguments

:: MonadBaseControl IO m 
=> m a

computation to run first

-> m b

computation to run afterward (even if an exception was raised)

-> m a 

Generalized version of finally.

Note, any monadic side effects in m of the "afterward" computation will be discarded.

onException :: MonadBaseControl IO m => m a -> m b -> m a #

Generalized version of onException.

Note, any monadic side effects in m of the "afterward" computation will be discarded.