ghc-8.2.2: The GHC API

Safe Haskell | None
Language | Haskell2010

Panic

Synopsis

- data GhcException
  - = Signal Int
  - | UsageError String
  - | CmdLineError String
  - | Panic String
  - | PprPanic String SDoc
  - | Sorry String
  - | PprSorry String SDoc
  - | InstallationError String
  - | ProgramError String
  - | PprProgramError String SDoc
- showGhcException :: GhcException -> ShowS
- throwGhcException :: GhcException -> a
- throwGhcExceptionIO :: GhcException -> IO a
- handleGhcException :: ExceptionMonad m => (GhcException -> m a) -> m a -> m a
- progName :: String
- pgmError :: String -> a
- panic :: String -> a
- sorry :: String -> a
- assertPanic :: String -> Int -> a
- trace :: String -> a -> a
- panicDoc :: String -> SDoc -> a
- sorryDoc :: String -> SDoc -> a
- pgmErrorDoc :: String -> SDoc -> a
- class (Typeable * e, Show e) => Exception e where
- showException :: Exception e => e -> String
- safeShowException :: Exception e => e -> IO String
- try :: Exception e => IO a -> IO (Either e a)
- tryMost :: IO a -> IO (Either SomeException a)
- throwTo :: Exception e => ThreadId -> e -> IO ()
- withSignalHandlers :: (ExceptionMonad m, MonadIO m) => m a -> m a

# Documentation

data GhcException #

GHC's own exception type error messages all take the form:

         location: error

If the location is on the command line, or in GHC itself, then location="ghc". All of the error types below correspond to a location of "ghc", except for ProgramError (where the string is assumed to contain a location already, so we don't print one).

Constructors

Signal Int | Some other fatal signal (SIGHUP,SIGTERM)
UsageError String | Prints the short usage msg after the error
CmdLineError String | A problem with the command line arguments, but don't print usage.
Panic String | The `impossible` happened.
PprPanic String SDoc |
Sorry String | The user tickled something that's known not to work yet, but we're not counting it as a bug.
PprSorry String SDoc |
InstallationError String | An installation problem.
ProgramError String | An error in the user's code, probably.
PprProgramError String SDoc |

Instances

Show GhcException # |
Methods showsPrec :: Int -> GhcException -> ShowS Source # show :: GhcException -> String Source # showList :: [GhcException] -> ShowS Source #
Exception GhcException # |
Methods toException :: GhcException -> SomeException Source # fromException :: SomeException -> Maybe GhcException Source # displayException :: GhcException -> String Source #

showGhcException :: GhcException -> ShowS #

Append a description of the given exception to this string.

Note that this uses `unsafeGlobalDynFlags`, which may have some uninitialized fields if invoked before `initGhcMonad` has been called. If the error message to be printed includes a pretty-printer document which forces one of these fields this call may bottom.

throwGhcException :: GhcException -> a #

throwGhcExceptionIO :: GhcException -> IO a #

handleGhcException :: ExceptionMonad m => (GhcException -> m a) -> m a -> m a #

progName :: String #

The name of this GHC.

pgmError :: String -> a #

Panics and asserts.

panic :: String -> a #

Panics and asserts.

sorry :: String -> a #

Panics and asserts.

assertPanic :: String -> Int -> a #

Throw an failed assertion exception for a given filename and line number.

trace :: String -> a -> a Source #

The `trace` function outputs the trace message given as its first argument, before returning the second argument as its result.

For example, this returns the value of `f x` but first outputs the message.

    trace ("calling f with x = " ++ show x) (f x)

The `trace` function should only be used for debugging, or for monitoring execution. The function is not referentially transparent: its type indicates that it is a pure function but it has the side effect of outputting the trace message.

panicDoc :: String -> SDoc -> a #

sorryDoc :: String -> SDoc -> a #

pgmErrorDoc :: String -> SDoc -> a #

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

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

Methods

toException :: e -> SomeException Source #

fromException :: SomeException -> Maybe e Source #

displayException :: e -> String Source #

Render this exception value in a human-friendly manner.

Default implementation: ``show``.

Since: 4.8.0.0

Instances

Exception Void | Since: 4.8.0.0
Methods toException :: Void -> SomeException Source # fromException :: SomeException -> Maybe Void Source # displayException :: Void -> String Source #
Exception PatternMatchFail | Since: 4.0
Methods toException :: PatternMatchFail -> SomeException Source # fromException :: SomeException -> Maybe PatternMatchFail Source # displayException :: PatternMatchFail -> String Source #
Exception RecSelError | Since: 4.0
Methods toException :: RecSelError -> SomeException Source # fromException :: SomeException -> Maybe RecSelError Source # displayException :: RecSelError -> String Source #
Exception RecConError | Since: 4.0
Methods toException :: RecConError -> SomeException Source # fromException :: SomeException -> Maybe RecConError Source # displayException :: RecConError -> String Source #
Exception RecUpdError | Since: 4.0
Methods toException :: RecUpdError -> SomeException Source # fromException :: SomeException -> Maybe RecUpdError Source # displayException :: RecUpdError -> String Source #
Exception NoMethodError | Since: 4.0
Methods toException :: NoMethodError -> SomeException Source # fromException :: SomeException -> Maybe NoMethodError Source # displayException :: NoMethodError -> String Source #
Exception TypeError | Since: 4.9.0.0
Methods toException :: TypeError -> SomeException Source # fromException :: SomeException -> Maybe TypeError Source # displayException :: TypeError -> String Source #
Exception NonTermination | Since: 4.0
Methods toException :: NonTermination -> SomeException Source # fromException :: SomeException -> Maybe NonTermination Source # displayException :: NonTermination -> String Source #
Exception NestedAtomically | Since: 4.0
Methods toException :: NestedAtomically -> SomeException Source # fromException :: SomeException -> Maybe NestedAtomically Source # displayException :: NestedAtomically -> String Source #
Exception Dynamic | Since: 4.0.0.0
Methods toException :: Dynamic -> SomeException Source # fromException :: SomeException -> Maybe Dynamic Source # displayException :: Dynamic -> String Source #
Exception BlockedIndefinitelyOnMVar | Since: 4.1.0.0
Methods toException :: BlockedIndefinitelyOnMVar -> SomeException Source # fromException :: SomeException -> Maybe BlockedIndefinitelyOnMVar Source # displayException :: BlockedIndefinitelyOnMVar -> String Source #
Exception BlockedIndefinitelyOnSTM | Since: 4.1.0.0
Methods toException :: BlockedIndefinitelyOnSTM -> SomeException Source # fromException :: SomeException -> Maybe BlockedIndefinitelyOnSTM Source # displayException :: BlockedIndefinitelyOnSTM -> String Source #
Exception Deadlock | Since: 4.1.0.0
Methods toException :: Deadlock -> SomeException Source # fromException :: SomeException -> Maybe Deadlock Source # displayException :: Deadlock -> String Source #
Exception AllocationLimitExceeded | Since: 4.8.0.0
Methods toException :: AllocationLimitExceeded -> SomeException Source # fromException :: SomeException -> Maybe AllocationLimitExceeded Source # displayException :: AllocationLimitExceeded -> String Source #
Exception CompactionFailed | Since: 4.10.0.0
Methods toException :: CompactionFailed -> SomeException Source # fromException :: SomeException -> Maybe CompactionFailed Source # displayException :: CompactionFailed -> String Source #
Exception AssertionFailed | Since: 4.1.0.0
Methods toException :: AssertionFailed -> SomeException Source # fromException :: SomeException -> Maybe AssertionFailed Source # displayException :: AssertionFailed -> String Source #
Exception SomeAsyncException | Since: 4.7.0.0
Methods toException :: SomeAsyncException -> SomeException Source # fromException :: SomeException -> Maybe SomeAsyncException Source # displayException :: SomeAsyncException -> String Source #
Exception AsyncException | Since: 4.7.0.0
Methods toException :: AsyncException -> SomeException Source # fromException :: SomeException -> Maybe AsyncException Source # displayException :: AsyncException -> String Source #
Exception ArrayException | Since: 4.1.0.0
Methods toException :: ArrayException -> SomeException Source # fromException :: SomeException -> Maybe ArrayException Source # displayException :: ArrayException -> String Source #
Exception ExitCode | Since: 4.1.0.0
Methods toException :: ExitCode -> SomeException Source # fromException :: SomeException -> Maybe ExitCode Source # displayException :: ExitCode -> String Source #
Exception IOException | Since: 4.1.0.0
Methods toException :: IOException -> SomeException Source # fromException :: SomeException -> Maybe IOException Source # displayException :: IOException -> String Source #
Exception ErrorCall | Since: 4.0.0.0
Methods toException :: ErrorCall -> SomeException Source # fromException :: SomeException -> Maybe ErrorCall Source # displayException :: ErrorCall -> String Source #
Exception ArithException | Since: 4.0.0.0
Methods toException :: ArithException -> SomeException Source # fromException :: SomeException -> Maybe ArithException Source # displayException :: ArithException -> String Source #
Exception SomeException | Since: 3.0
Methods toException :: SomeException -> SomeException Source # fromException :: SomeException -> Maybe SomeException Source # displayException :: SomeException -> String Source #
Exception SetupTermError |
Methods toException :: SetupTermError -> SomeException Source # fromException :: SomeException -> Maybe SetupTermError Source # displayException :: SetupTermError -> String Source #
Exception GhcException # |
Methods toException :: GhcException -> SomeException Source # fromException :: SomeException -> Maybe GhcException Source # displayException :: GhcException -> String Source #
Exception IOEnvFailure # |
Methods toException :: IOEnvFailure -> SomeException Source # fromException :: SomeException -> Maybe IOEnvFailure Source # displayException :: IOEnvFailure -> String Source #
Exception GhcApiError # |
Methods toException :: GhcApiError -> SomeException Source # fromException :: SomeException -> Maybe GhcApiError Source # displayException :: GhcApiError -> String Source #
Exception SourceError # |
Methods toException :: SourceError -> SomeException Source # fromException :: SomeException -> Maybe SourceError Source # displayException :: SourceError -> String Source #

showException :: Exception e => e -> String #

Show an exception as a string.

safeShowException :: Exception e => e -> IO String #

Show an exception which can possibly throw other exceptions. Used when displaying exception thrown within TH code.

try :: Exception e => IO a -> IO (Either e a) Source #

Similar to `catch`, but returns an `Either` result which is `(`Right` a)` if no exception of type `e` was raised, or `(`Left` ex)` if an exception of type `e` was raised and its value is `ex`. If any other type of exception is raised than it will be propogated up to the next enclosing exception handler.

     try a = catch (Right `liftM` a) (return . Left)

tryMost :: IO a -> IO (Either SomeException a) #

Like try, but pass through UserInterrupt and Panic exceptions. Used when we want soft failures when reading interface files, for example. TODO: I'm not entirely sure if this is catching what we really want to catch

throwTo :: Exception e => ThreadId -> e -> IO () Source #

`throwTo` raises an arbitrary exception in the target thread (GHC only).

Exception delivery synchronizes between the source and target thread: `throwTo` does not return until the exception has been raised in the target thread. The calling thread can thus be certain that the target thread has received the exception. Exception delivery is also atomic with respect to other exceptions. Atomicity is a useful property to have when dealing with race conditions: e.g. if there are two threads that can kill each other, it is guaranteed that only one of the threads will get to kill the other.

Whatever work the target thread was doing when the exception was raised is not lost: the computation is suspended until required by another thread.

If the target thread is currently making a foreign call, then the exception will not be raised (and hence `throwTo` will not return) until the call has completed. This is the case regardless of whether the call is inside a `mask` or not. However, in GHC a foreign call can be annotated as `interruptible`, in which case a `throwTo` will cause the RTS to attempt to cause the call to return; see the GHC documentation for more details.

Important note: the behaviour of `throwTo` differs from that described in the paper "Asynchronous exceptions in Haskell" (http://research.microsoft.com/~simonpj/Papers/asynch-exns.htm). In the paper, `throwTo` is non-blocking; but the library implementation adopts a more synchronous design in which `throwTo` does not return until the exception is received by the target thread. The trade-off is discussed in Section 9 of the paper. Like any blocking operation, `throwTo` is therefore interruptible (see Section 5.3 of the paper). Unlike other interruptible operations, however, `throwTo` is always interruptible, even if it does not actually block.

There is no guarantee that the exception will be delivered promptly, although the runtime will endeavour to ensure that arbitrary delays don't occur. In GHC, an exception can only be raised when a thread reaches a safe point, where a safe point is where memory allocation occurs. Some loops do not perform any memory allocation inside the loop and therefore cannot be interrupted by a `throwTo`.

If the target of `throwTo` is the calling thread, then the behaviour is the same as `throwIO`, except that the exception is thrown as an asynchronous exception. This means that if there is an enclosing pure computation, which would be the case if the current IO operation is inside `unsafePerformIO` or `unsafeInterleaveIO`, that computation is not permanently replaced by the exception, but is suspended as if it had received an asynchronous exception.

Note that if `throwTo` is called with the current thread as the target, the exception will be thrown even if the thread is currently inside `mask` or `uninterruptibleMask`.

withSignalHandlers :: (ExceptionMonad m, MonadIO m) => m a -> m a #

Temporarily install standard signal handlers for catching ^C, which just throw an exception in the current thread.