2 {-# OPTIONS_GHC -XNoImplicitPrelude -funbox-strict-fields #-}
3 {-# OPTIONS_HADDOCK hide #-}
4 -----------------------------------------------------------------------------
7 -- Copyright : (c) The University of Glasgow 1994-2002
8 -- License : see libraries/base/LICENSE
10 -- Maintainer : cvs-ghc@haskell.org
11 -- Stability : internal
12 -- Portability : non-portable (GHC Extensions)
14 -- Definitions for the 'IO' monad and its friends.
16 -----------------------------------------------------------------------------
20 IO(..), unIO, failIO, liftIO, bindIO, thenIO, returnIO,
21 unsafePerformIO, unsafeInterleaveIO,
22 unsafeDupablePerformIO, unsafeDupableInterleaveIO,
25 -- To and from from ST
26 stToIO, ioToST, unsafeIOToST, unsafeSTToIO,
29 IORef(..), newIORef, readIORef, writeIORef,
30 IOArray(..), newIOArray, readIOArray, writeIOArray, unsafeReadIOArray, unsafeWriteIOArray,
33 -- Handles, file descriptors,
35 Handle(..), Handle__(..), HandleType(..), IOMode(..), FD,
36 isReadableHandleType, isWritableHandleType, isReadWriteHandleType, showHandle,
39 Buffer(..), RawBuffer, BufferState(..), BufferList(..), BufferMode(..),
40 bufferIsWritable, bufferEmpty, bufferFull,
43 Exception(..), ArithException(..), AsyncException(..), ArrayException(..),
44 stackOverflow, heapOverflow, ioException,
45 IOError, IOException(..), IOErrorType(..), ioError, userError,
47 throwIO, block, unblock, blocked, catchAny, catchException,
49 ErrorCall(..), AssertionFailed(..), assertError, untangle,
50 BlockedOnDeadMVar(..), BlockedIndefinitely(..), Deadlock(..)
54 import GHC.Arr -- to derive Ix class
55 import GHC.Enum -- to derive Enum class
58 -- import GHC.Num -- To get fromInteger etc, needed because of -XNoImplicitPrelude
59 import Data.Maybe ( Maybe(..) )
63 import Foreign.C.Types (CInt)
67 import {-# SOURCE #-} Data.Typeable ( Typeable )
70 -- ---------------------------------------------------------------------------
74 The IO Monad is just an instance of the ST monad, where the state is
75 the real world. We use the exception mechanism (in GHC.Exception) to
76 implement IO exceptions.
78 NOTE: The IO representation is deeply wired in to various parts of the
79 system. The following list may or may not be exhaustive:
81 Compiler - types of various primitives in PrimOp.lhs
83 RTS - forceIO (StgMiscClosures.hc)
84 - catchzh_fast, (un)?blockAsyncExceptionszh_fast, raisezh_fast
86 - raiseAsync (Schedule.c)
88 Prelude - GHC.IOBase.lhs, and several other places including
91 Libraries - parts of hslibs/lang.
97 A value of type @'IO' a@ is a computation which, when performed,
98 does some I\/O before returning a value of type @a@.
100 There is really only one way to \"perform\" an I\/O action: bind it to
101 @Main.main@ in your program. When your program is run, the I\/O will
102 be performed. It isn't possible to perform I\/O from an arbitrary
103 function, unless that function is itself in the 'IO' monad and called
104 at some point, directly or indirectly, from @Main.main@.
106 'IO' is a monad, so 'IO' actions can be combined using either the do-notation
107 or the '>>' and '>>=' operations from the 'Monad' class.
109 newtype IO a = IO (State# RealWorld -> (# State# RealWorld, a #))
111 unIO :: IO a -> (State# RealWorld -> (# State# RealWorld, a #))
114 instance Functor IO where
115 fmap f x = x >>= (return . f)
117 instance Monad IO where
118 {-# INLINE return #-}
121 m >> k = m >>= \ _ -> k
122 return x = returnIO x
127 failIO :: String -> IO a
128 failIO s = ioError (userError s)
130 liftIO :: IO a -> State# RealWorld -> STret RealWorld a
131 liftIO (IO m) = \s -> case m s of (# s', r #) -> STret s' r
133 bindIO :: IO a -> (a -> IO b) -> IO b
134 bindIO (IO m) k = IO ( \ s ->
136 (# new_s, a #) -> unIO (k a) new_s
139 thenIO :: IO a -> IO b -> IO b
140 thenIO (IO m) k = IO ( \ s ->
142 (# new_s, _ #) -> unIO k new_s
145 returnIO :: a -> IO a
146 returnIO x = IO (\ s -> (# s, x #))
148 -- ---------------------------------------------------------------------------
149 -- Coercions between IO and ST
151 -- | A monad transformer embedding strict state transformers in the 'IO'
152 -- monad. The 'RealWorld' parameter indicates that the internal state
153 -- used by the 'ST' computation is a special one supplied by the 'IO'
154 -- monad, and thus distinct from those used by invocations of 'runST'.
155 stToIO :: ST RealWorld a -> IO a
158 ioToST :: IO a -> ST RealWorld a
159 ioToST (IO m) = (ST m)
161 -- This relies on IO and ST having the same representation modulo the
162 -- constraint on the type of the state
164 unsafeIOToST :: IO a -> ST s a
165 unsafeIOToST (IO io) = ST $ \ s -> (unsafeCoerce# io) s
167 unsafeSTToIO :: ST s a -> IO a
168 unsafeSTToIO (ST m) = IO (unsafeCoerce# m)
170 -- ---------------------------------------------------------------------------
171 -- Unsafe IO operations
174 This is the \"back door\" into the 'IO' monad, allowing
175 'IO' computation to be performed at any time. For
176 this to be safe, the 'IO' computation should be
177 free of side effects and independent of its environment.
179 If the I\/O computation wrapped in 'unsafePerformIO'
180 performs side effects, then the relative order in which those side
181 effects take place (relative to the main I\/O trunk, or other calls to
182 'unsafePerformIO') is indeterminate. You have to be careful when
183 writing and compiling modules that use 'unsafePerformIO':
185 * Use @{\-\# NOINLINE foo \#-\}@ as a pragma on any function @foo@
186 that calls 'unsafePerformIO'. If the call is inlined,
187 the I\/O may be performed more than once.
189 * Use the compiler flag @-fno-cse@ to prevent common sub-expression
190 elimination being performed on the module, which might combine
191 two side effects that were meant to be separate. A good example
192 is using multiple global variables (like @test@ in the example below).
194 * Make sure that the either you switch off let-floating, or that the
195 call to 'unsafePerformIO' cannot float outside a lambda. For example,
198 f x = unsafePerformIO (newIORef [])
200 you may get only one reference cell shared between all calls to @f@.
203 f x = unsafePerformIO (newIORef [x])
205 because now it can't float outside the lambda.
207 It is less well known that
208 'unsafePerformIO' is not type safe. For example:
211 > test = unsafePerformIO $ newIORef []
214 > writeIORef test [42]
215 > bang <- readIORef test
216 > print (bang :: [Char])
218 This program will core dump. This problem with polymorphic references
219 is well known in the ML community, and does not arise with normal
220 monadic use of references. There is no easy way to make it impossible
221 once you use 'unsafePerformIO'. Indeed, it is
222 possible to write @coerce :: a -> b@ with the
223 help of 'unsafePerformIO'. So be careful!
225 unsafePerformIO :: IO a -> a
226 unsafePerformIO m = unsafeDupablePerformIO (noDuplicate >> m)
229 This version of 'unsafePerformIO' is slightly more efficient,
230 because it omits the check that the IO is only being performed by a
231 single thread. Hence, when you write 'unsafeDupablePerformIO',
232 there is a possibility that the IO action may be performed multiple
233 times (on a multiprocessor), and you should therefore ensure that
234 it gives the same results each time.
236 {-# NOINLINE unsafeDupablePerformIO #-}
237 unsafeDupablePerformIO :: IO a -> a
238 unsafeDupablePerformIO (IO m) = lazy (case m realWorld# of (# _, r #) -> r)
240 -- Why do we NOINLINE unsafeDupablePerformIO? See the comment with
241 -- GHC.ST.runST. Essentially the issue is that the IO computation
242 -- inside unsafePerformIO must be atomic: it must either all run, or
243 -- not at all. If we let the compiler see the application of the IO
244 -- to realWorld#, it might float out part of the IO.
246 -- Why is there a call to 'lazy' in unsafeDupablePerformIO?
247 -- If we don't have it, the demand analyser discovers the following strictness
248 -- for unsafeDupablePerformIO: C(U(AV))
250 -- unsafeDupablePerformIO (\s -> let r = f x in
251 -- case writeIORef v r s of (# s1, _ #) ->
253 -- The strictness analyser will find that the binding for r is strict,
254 -- (becuase of uPIO's strictness sig), and so it'll evaluate it before
255 -- doing the writeIORef. This actually makes tests/lib/should_run/memo002
258 -- Solution: don't expose the strictness of unsafeDupablePerformIO,
259 -- by hiding it with 'lazy'
262 'unsafeInterleaveIO' allows 'IO' computation to be deferred lazily.
263 When passed a value of type @IO a@, the 'IO' will only be performed
264 when the value of the @a@ is demanded. This is used to implement lazy
265 file reading, see 'System.IO.hGetContents'.
267 {-# INLINE unsafeInterleaveIO #-}
268 unsafeInterleaveIO :: IO a -> IO a
269 unsafeInterleaveIO m = unsafeDupableInterleaveIO (noDuplicate >> m)
271 -- We believe that INLINE on unsafeInterleaveIO is safe, because the
272 -- state from this IO thread is passed explicitly to the interleaved
273 -- IO, so it cannot be floated out and shared.
275 {-# INLINE unsafeDupableInterleaveIO #-}
276 unsafeDupableInterleaveIO :: IO a -> IO a
277 unsafeDupableInterleaveIO (IO m)
279 r = case m s of (# _, res #) -> res
284 Ensures that the suspensions under evaluation by the current thread
285 are unique; that is, the current thread is not evaluating anything
286 that is also under evaluation by another thread that has also executed
289 This operation is used in the definition of 'unsafePerformIO' to
290 prevent the IO action from being executed multiple times, which is usually
294 noDuplicate = IO $ \s -> case noDuplicate# s of s' -> (# s', () #)
296 -- ---------------------------------------------------------------------------
299 data MVar a = MVar (MVar# RealWorld a)
301 An 'MVar' (pronounced \"em-var\") is a synchronising variable, used
302 for communication between concurrent threads. It can be thought of
303 as a a box, which may be empty or full.
306 -- pull in Eq (Mvar a) too, to avoid GHC.Conc being an orphan-instance module
307 instance Eq (MVar a) where
308 (MVar mvar1#) == (MVar mvar2#) = sameMVar# mvar1# mvar2#
310 -- A Handle is represented by (a reference to) a record
311 -- containing the state of the I/O port/device. We record
312 -- the following pieces of info:
314 -- * type (read,write,closed etc.)
315 -- * the underlying file descriptor
317 -- * buffer, and spare buffers
318 -- * user-friendly name (usually the
319 -- FilePath used when IO.openFile was called)
321 -- Note: when a Handle is garbage collected, we want to flush its buffer
322 -- and close the OS file handle, so as to free up a (precious) resource.
324 -- | Haskell defines operations to read and write characters from and to files,
325 -- represented by values of type @Handle@. Each value of this type is a
326 -- /handle/: a record used by the Haskell run-time system to /manage/ I\/O
327 -- with file system objects. A handle has at least the following properties:
329 -- * whether it manages input or output or both;
331 -- * whether it is /open/, /closed/ or /semi-closed/;
333 -- * whether the object is seekable;
335 -- * whether buffering is disabled, or enabled on a line or block basis;
337 -- * a buffer (whose length may be zero).
339 -- Most handles will also have a current I\/O position indicating where the next
340 -- input or output operation will occur. A handle is /readable/ if it
341 -- manages only input or both input and output; likewise, it is /writable/ if
342 -- it manages only output or both input and output. A handle is /open/ when
344 -- Once it is closed it can no longer be used for either input or output,
345 -- though an implementation cannot re-use its storage while references
346 -- remain to it. Handles are in the 'Show' and 'Eq' classes. The string
347 -- produced by showing a handle is system dependent; it should include
348 -- enough information to identify the handle for debugging. A handle is
349 -- equal according to '==' only to itself; no attempt
350 -- is made to compare the internal state of different handles for equality.
352 -- GHC note: a 'Handle' will be automatically closed when the garbage
353 -- collector detects that it has become unreferenced by the program.
354 -- However, relying on this behaviour is not generally recommended:
355 -- the garbage collector is unpredictable. If possible, use explicit
356 -- an explicit 'hClose' to close 'Handle's when they are no longer
357 -- required. GHC does not currently attempt to free up file
358 -- descriptors when they have run out, it is your responsibility to
359 -- ensure that this doesn't happen.
362 = FileHandle -- A normal handle to a file
363 FilePath -- the file (invariant)
366 | DuplexHandle -- A handle to a read/write stream
367 FilePath -- file for a FIFO, otherwise some
368 -- descriptive string.
369 !(MVar Handle__) -- The read side
370 !(MVar Handle__) -- The write side
373 -- * A 'FileHandle' is seekable. A 'DuplexHandle' may or may not be
376 instance Eq Handle where
377 (FileHandle _ h1) == (FileHandle _ h2) = h1 == h2
378 (DuplexHandle _ h1 _) == (DuplexHandle _ h2 _) = h1 == h2
385 haFD :: !FD, -- file descriptor
386 haType :: HandleType, -- type (read/write/append etc.)
387 haIsBin :: Bool, -- binary mode?
388 haIsStream :: Bool, -- Windows : is this a socket?
389 -- Unix : is O_NONBLOCK set?
390 haBufferMode :: BufferMode, -- buffer contains read/write data?
391 haBuffer :: !(IORef Buffer), -- the current buffer
392 haBuffers :: !(IORef BufferList), -- spare buffers
393 haOtherSide :: Maybe (MVar Handle__) -- ptr to the write side of a
397 -- ---------------------------------------------------------------------------
400 -- The buffer is represented by a mutable variable containing a
401 -- record, where the record contains the raw buffer and the start/end
402 -- points of the filled portion. We use a mutable variable so that
403 -- the common operation of writing (or reading) some data from (to)
404 -- the buffer doesn't need to modify, and hence copy, the handle
405 -- itself, it just updates the buffer.
407 -- There will be some allocation involved in a simple hPutChar in
408 -- order to create the new Buffer structure (below), but this is
409 -- relatively small, and this only has to be done once per write
412 -- The buffer contains its size - we could also get the size by
413 -- calling sizeOfMutableByteArray# on the raw buffer, but that tends
414 -- to be rounded up to the nearest Word.
416 type RawBuffer = MutableByteArray# RealWorld
418 -- INVARIANTS on a Buffer:
420 -- * A handle *always* has a buffer, even if it is only 1 character long
421 -- (an unbuffered handle needs a 1 character buffer in order to support
422 -- hLookAhead and hIsEOF).
424 -- * if r == w, then r == 0 && w == 0
425 -- * if state == WriteBuffer, then r == 0
426 -- * a write buffer is never full. If an operation
427 -- fills up the buffer, it will always flush it before
429 -- * a read buffer may be full as a result of hLookAhead. In normal
430 -- operation, a read buffer always has at least one character of space.
438 bufState :: BufferState
441 data BufferState = ReadBuffer | WriteBuffer deriving (Eq)
443 -- we keep a few spare buffers around in a handle to avoid allocating
444 -- a new one for each hPutStr. These buffers are *guaranteed* to be the
445 -- same size as the main buffer.
448 | BufferListCons RawBuffer BufferList
451 bufferIsWritable :: Buffer -> Bool
452 bufferIsWritable Buffer{ bufState=WriteBuffer } = True
453 bufferIsWritable _other = False
455 bufferEmpty :: Buffer -> Bool
456 bufferEmpty Buffer{ bufRPtr=r, bufWPtr=w } = r == w
458 -- only makes sense for a write buffer
459 bufferFull :: Buffer -> Bool
460 bufferFull b@Buffer{ bufWPtr=w } = w >= bufSize b
462 -- Internally, we classify handles as being one
473 isReadableHandleType :: HandleType -> Bool
474 isReadableHandleType ReadHandle = True
475 isReadableHandleType ReadWriteHandle = True
476 isReadableHandleType _ = False
478 isWritableHandleType :: HandleType -> Bool
479 isWritableHandleType AppendHandle = True
480 isWritableHandleType WriteHandle = True
481 isWritableHandleType ReadWriteHandle = True
482 isWritableHandleType _ = False
484 isReadWriteHandleType :: HandleType -> Bool
485 isReadWriteHandleType ReadWriteHandle{} = True
486 isReadWriteHandleType _ = False
488 -- | File and directory names are values of type 'String', whose precise
489 -- meaning is operating system dependent. Files can be opened, yielding a
490 -- handle which can then be used to operate on the contents of that file.
492 type FilePath = String
494 -- ---------------------------------------------------------------------------
497 -- | Three kinds of buffering are supported: line-buffering,
498 -- block-buffering or no-buffering. These modes have the following
499 -- effects. For output, items are written out, or /flushed/,
500 -- from the internal buffer according to the buffer mode:
502 -- * /line-buffering/: the entire output buffer is flushed
503 -- whenever a newline is output, the buffer overflows,
504 -- a 'System.IO.hFlush' is issued, or the handle is closed.
506 -- * /block-buffering/: the entire buffer is written out whenever it
507 -- overflows, a 'System.IO.hFlush' is issued, or the handle is closed.
509 -- * /no-buffering/: output is written immediately, and never stored
512 -- An implementation is free to flush the buffer more frequently,
513 -- but not less frequently, than specified above.
514 -- The output buffer is emptied as soon as it has been written out.
516 -- Similarly, input occurs according to the buffer mode for the handle:
518 -- * /line-buffering/: when the buffer for the handle is not empty,
519 -- the next item is obtained from the buffer; otherwise, when the
520 -- buffer is empty, characters up to and including the next newline
521 -- character are read into the buffer. No characters are available
522 -- until the newline character is available or the buffer is full.
524 -- * /block-buffering/: when the buffer for the handle becomes empty,
525 -- the next block of data is read into the buffer.
527 -- * /no-buffering/: the next input item is read and returned.
528 -- The 'System.IO.hLookAhead' operation implies that even a no-buffered
529 -- handle may require a one-character buffer.
531 -- The default buffering mode when a handle is opened is
532 -- implementation-dependent and may depend on the file system object
533 -- which is attached to that handle.
534 -- For most implementations, physical files will normally be block-buffered
535 -- and terminals will normally be line-buffered.
538 = NoBuffering -- ^ buffering is disabled if possible.
540 -- ^ line-buffering should be enabled if possible.
541 | BlockBuffering (Maybe Int)
542 -- ^ block-buffering should be enabled if possible.
543 -- The size of the buffer is @n@ items if the argument
544 -- is 'Just' @n@ and is otherwise implementation-dependent.
545 deriving (Eq, Ord, Read, Show)
547 -- ---------------------------------------------------------------------------
550 -- |A mutable variable in the 'IO' monad
551 newtype IORef a = IORef (STRef RealWorld a)
553 -- explicit instance because Haddock can't figure out a derived one
554 instance Eq (IORef a) where
555 IORef x == IORef y = x == y
557 -- |Build a new 'IORef'
558 newIORef :: a -> IO (IORef a)
559 newIORef v = stToIO (newSTRef v) >>= \ var -> return (IORef var)
561 -- |Read the value of an 'IORef'
562 readIORef :: IORef a -> IO a
563 readIORef (IORef var) = stToIO (readSTRef var)
565 -- |Write a new value into an 'IORef'
566 writeIORef :: IORef a -> a -> IO ()
567 writeIORef (IORef var) v = stToIO (writeSTRef var v)
569 -- ---------------------------------------------------------------------------
570 -- | An 'IOArray' is a mutable, boxed, non-strict array in the 'IO' monad.
571 -- The type arguments are as follows:
573 -- * @i@: the index type of the array (should be an instance of 'Ix')
575 -- * @e@: the element type of the array.
579 newtype IOArray i e = IOArray (STArray RealWorld i e)
581 -- explicit instance because Haddock can't figure out a derived one
582 instance Eq (IOArray i e) where
583 IOArray x == IOArray y = x == y
585 -- |Build a new 'IOArray'
586 newIOArray :: Ix i => (i,i) -> e -> IO (IOArray i e)
587 {-# INLINE newIOArray #-}
588 newIOArray lu initial = stToIO $ do {marr <- newSTArray lu initial; return (IOArray marr)}
590 -- | Read a value from an 'IOArray'
591 unsafeReadIOArray :: Ix i => IOArray i e -> Int -> IO e
592 {-# INLINE unsafeReadIOArray #-}
593 unsafeReadIOArray (IOArray marr) i = stToIO (unsafeReadSTArray marr i)
595 -- | Write a new value into an 'IOArray'
596 unsafeWriteIOArray :: Ix i => IOArray i e -> Int -> e -> IO ()
597 {-# INLINE unsafeWriteIOArray #-}
598 unsafeWriteIOArray (IOArray marr) i e = stToIO (unsafeWriteSTArray marr i e)
600 -- | Read a value from an 'IOArray'
601 readIOArray :: Ix i => IOArray i e -> i -> IO e
602 readIOArray (IOArray marr) i = stToIO (readSTArray marr i)
604 -- | Write a new value into an 'IOArray'
605 writeIOArray :: Ix i => IOArray i e -> i -> e -> IO ()
606 writeIOArray (IOArray marr) i e = stToIO (writeSTArray marr i e)
609 -- ---------------------------------------------------------------------------
610 -- Show instance for Handles
612 -- handle types are 'show'n when printing error msgs, so
613 -- we provide a more user-friendly Show instance for it
614 -- than the derived one.
616 instance Show HandleType where
619 ClosedHandle -> showString "closed"
620 SemiClosedHandle -> showString "semi-closed"
621 ReadHandle -> showString "readable"
622 WriteHandle -> showString "writable"
623 AppendHandle -> showString "writable (append)"
624 ReadWriteHandle -> showString "read-writable"
626 instance Show Handle where
627 showsPrec _ (FileHandle file _) = showHandle file
628 showsPrec _ (DuplexHandle file _ _) = showHandle file
630 showHandle :: FilePath -> String -> String
631 showHandle file = showString "{handle: " . showString file . showString "}"
633 -- ------------------------------------------------------------------------
634 -- Exception datatypes and operations
636 data BlockedOnDeadMVar = BlockedOnDeadMVar
639 instance Exception BlockedOnDeadMVar
641 instance Show BlockedOnDeadMVar where
642 showsPrec _ BlockedOnDeadMVar = showString "thread blocked indefinitely"
646 data BlockedIndefinitely = BlockedIndefinitely
649 instance Exception BlockedIndefinitely
651 instance Show BlockedIndefinitely where
652 showsPrec _ BlockedIndefinitely = showString "thread blocked indefinitely"
656 data Deadlock = Deadlock
659 instance Exception Deadlock
661 instance Show Deadlock where
662 showsPrec _ Deadlock = showString "<<deadlock>>"
666 data AssertionFailed = AssertionFailed String
669 instance Exception AssertionFailed
671 instance Show AssertionFailed where
672 showsPrec _ (AssertionFailed err) = showString err
676 -- |Asynchronous exceptions
679 -- ^The current thread\'s stack exceeded its limit.
680 -- Since an exception has been raised, the thread\'s stack
681 -- will certainly be below its limit again, but the
682 -- programmer should take remedial action
685 -- ^The program\'s heap is reaching its limit, and
686 -- the program should take action to reduce the amount of
687 -- live data it has. Notes:
689 -- * It is undefined which thread receives this exception.
691 -- * GHC currently does not throw 'HeapOverflow' exceptions.
693 -- ^This exception is raised by another thread
694 -- calling 'Control.Concurrent.killThread', or by the system
695 -- if it needs to terminate the thread for some
698 -- ^This exception is raised by default in the main thread of
699 -- the program when the user requests to terminate the program
700 -- via the usual mechanism(s) (e.g. Control-C in the console).
701 deriving (Eq, Ord, Typeable)
703 instance Exception AsyncException
705 -- | Exceptions generated by array operations
707 = IndexOutOfBounds String
708 -- ^An attempt was made to index an array outside
709 -- its declared bounds.
710 | UndefinedElement String
711 -- ^An attempt was made to evaluate an element of an
712 -- array that had not been initialized.
713 deriving (Eq, Ord, Typeable)
715 instance Exception ArrayException
717 stackOverflow, heapOverflow :: SomeException -- for the RTS
718 stackOverflow = toException StackOverflow
719 heapOverflow = toException HeapOverflow
721 instance Show AsyncException where
722 showsPrec _ StackOverflow = showString "stack overflow"
723 showsPrec _ HeapOverflow = showString "heap overflow"
724 showsPrec _ ThreadKilled = showString "thread killed"
725 showsPrec _ UserInterrupt = showString "user interrupt"
727 instance Show ArrayException where
728 showsPrec _ (IndexOutOfBounds s)
729 = showString "array index out of range"
730 . (if not (null s) then showString ": " . showString s
732 showsPrec _ (UndefinedElement s)
733 = showString "undefined array element"
734 . (if not (null s) then showString ": " . showString s
737 -- -----------------------------------------------------------------------------
740 -- We need it here because it is used in ExitException in the
741 -- Exception datatype (above).
744 = ExitSuccess -- ^ indicates successful termination;
746 -- ^ indicates program failure with an exit code.
747 -- The exact interpretation of the code is
748 -- operating-system dependent. In particular, some values
749 -- may be prohibited (e.g. 0 on a POSIX-compliant system).
750 deriving (Eq, Ord, Read, Show, Typeable)
752 instance Exception ExitCode
754 ioException :: IOException -> IO a
755 ioException err = throwIO err
757 -- | Raise an 'IOError' in the 'IO' monad.
758 ioError :: IOError -> IO a
759 ioError = ioException
761 -- ---------------------------------------------------------------------------
764 -- | The Haskell 98 type for exceptions in the 'IO' monad.
765 -- Any I\/O operation may raise an 'IOError' instead of returning a result.
766 -- For a more general type of exception, including also those that arise
767 -- in pure code, see 'Control.Exception.Exception'.
769 -- In Haskell 98, this is an opaque type.
770 type IOError = IOException
772 -- |Exceptions that occur in the @IO@ monad.
773 -- An @IOException@ records a more specific error type, a descriptive
774 -- string and maybe the handle that was used when the error was
778 ioe_handle :: Maybe Handle, -- the handle used by the action flagging
780 ioe_type :: IOErrorType, -- what it was.
781 ioe_location :: String, -- location.
782 ioe_description :: String, -- error type specific information.
783 ioe_filename :: Maybe FilePath -- filename the error is related to.
787 instance Exception IOException
789 instance Eq IOException where
790 (IOError h1 e1 loc1 str1 fn1) == (IOError h2 e2 loc2 str2 fn2) =
791 e1==e2 && str1==str2 && h1==h2 && loc1==loc2 && fn1==fn2
793 -- | An abstract type that contains a value for each variant of 'IOError'.
805 | UnsatisfiedConstraints
812 | UnsupportedOperation
817 instance Eq IOErrorType where
818 x == y = getTag x ==# getTag y
820 instance Show IOErrorType where
824 AlreadyExists -> "already exists"
825 NoSuchThing -> "does not exist"
826 ResourceBusy -> "resource busy"
827 ResourceExhausted -> "resource exhausted"
829 IllegalOperation -> "illegal operation"
830 PermissionDenied -> "permission denied"
831 UserError -> "user error"
832 HardwareFault -> "hardware fault"
833 InappropriateType -> "inappropriate type"
834 Interrupted -> "interrupted"
835 InvalidArgument -> "invalid argument"
836 OtherError -> "failed"
837 ProtocolError -> "protocol error"
838 ResourceVanished -> "resource vanished"
839 SystemError -> "system error"
840 TimeExpired -> "timeout"
841 UnsatisfiedConstraints -> "unsatisified constraints" -- ultra-precise!
842 UnsupportedOperation -> "unsupported operation"
844 -- | Construct an 'IOError' value with a string describing the error.
845 -- The 'fail' method of the 'IO' instance of the 'Monad' class raises a
846 -- 'userError', thus:
848 -- > instance Monad IO where
850 -- > fail s = ioError (userError s)
852 userError :: String -> IOError
853 userError str = IOError Nothing UserError "" str Nothing
855 -- ---------------------------------------------------------------------------
858 instance Show IOException where
859 showsPrec p (IOError hdl iot loc s fn) =
861 Nothing -> case hdl of
863 Just h -> showsPrec p h . showString ": "
864 Just name -> showString name . showString ": ") .
867 _ -> showString loc . showString ": ") .
871 _ -> showString " (" . showString s . showString ")")
873 -- -----------------------------------------------------------------------------
876 data IOMode = ReadMode | WriteMode | AppendMode | ReadWriteMode
877 deriving (Eq, Ord, Ix, Enum, Read, Show)
880 %*********************************************************
882 \subsection{Primitive catch and throwIO}
884 %*********************************************************
886 catchException used to handle the passing around of the state to the
887 action and the handler. This turned out to be a bad idea - it meant
888 that we had to wrap both arguments in thunks so they could be entered
889 as normal (remember IO returns an unboxed pair...).
893 catch# :: IO a -> (b -> IO a) -> IO a
895 (well almost; the compiler doesn't know about the IO newtype so we
896 have to work around that in the definition of catchException below).
899 catchException :: Exception e => IO a -> (e -> IO a) -> IO a
900 catchException (IO io) handler = IO $ catch# io handler'
901 where handler' e = case fromException e of
902 Just e' -> unIO (handler e')
905 catchAny :: IO a -> (forall e . Exception e => e -> IO a) -> IO a
906 catchAny (IO io) handler = IO $ catch# io handler'
907 where handler' (SomeException e) = unIO (handler e)
909 -- | A variant of 'throw' that can be used within the 'IO' monad.
911 -- Although 'throwIO' has a type that is an instance of the type of 'throw', the
912 -- two functions are subtly different:
914 -- > throw e `seq` x ===> throw e
915 -- > throwIO e `seq` x ===> x
917 -- The first example will cause the exception @e@ to be raised,
918 -- whereas the second one won\'t. In fact, 'throwIO' will only cause
919 -- an exception to be raised when it is used within the 'IO' monad.
920 -- The 'throwIO' variant should be used in preference to 'throw' to
921 -- raise an exception within the 'IO' monad because it guarantees
922 -- ordering with respect to other 'IO' operations, whereas 'throw'
924 throwIO :: Exception e => e -> IO a
925 throwIO e = IO (raiseIO# (toException e))
929 %*********************************************************
931 \subsection{Controlling asynchronous exception delivery}
933 %*********************************************************
936 -- | Applying 'block' to a computation will
937 -- execute that computation with asynchronous exceptions
938 -- /blocked/. That is, any thread which
939 -- attempts to raise an exception in the current thread with 'Control.Exception.throwTo' will be
940 -- blocked until asynchronous exceptions are enabled again. There\'s
941 -- no need to worry about re-enabling asynchronous exceptions; that is
942 -- done automatically on exiting the scope of
945 -- Threads created by 'Control.Concurrent.forkIO' inherit the blocked
946 -- state from the parent; that is, to start a thread in blocked mode,
947 -- use @block $ forkIO ...@. This is particularly useful if you need to
948 -- establish an exception handler in the forked thread before any
949 -- asynchronous exceptions are received.
950 block :: IO a -> IO a
952 -- | To re-enable asynchronous exceptions inside the scope of
953 -- 'block', 'unblock' can be
954 -- used. It scopes in exactly the same way, so on exit from
955 -- 'unblock' asynchronous exception delivery will
956 -- be disabled again.
957 unblock :: IO a -> IO a
959 block (IO io) = IO $ blockAsyncExceptions# io
960 unblock (IO io) = IO $ unblockAsyncExceptions# io
962 -- | returns True if asynchronous exceptions are blocked in the
965 blocked = IO $ \s -> case asyncExceptionsBlocked# s of
966 (# s', i #) -> (# s', i /=# 0# #)
970 -- | Forces its argument to be evaluated when the resultant 'IO' action
971 -- is executed. It can be used to order evaluation with respect to
972 -- other 'IO' operations; its semantics are given by
974 -- > evaluate x `seq` y ==> y
975 -- > evaluate x `catch` f ==> (return $! x) `catch` f
976 -- > evaluate x >>= f ==> (return $! x) >>= f
978 -- /Note:/ the first equation implies that @(evaluate x)@ is /not/ the
979 -- same as @(return $! x)@. A correct definition is
981 -- > evaluate x = (return $! x) >>= return
983 evaluate :: a -> IO a
984 evaluate a = IO $ \s -> case a `seq` () of () -> (# s, a #)
986 -- a `seq` (# s, a #)
987 -- because we can't have an unboxed tuple as a function argument
991 assertError :: Addr# -> Bool -> a -> a
992 assertError str predicate v
994 | otherwise = throw (AssertionFailed (untangle str "Assertion failed"))
997 (untangle coded message) expects "coded" to be of the form
1000 location message details
1002 untangle :: Addr# -> String -> String
1003 untangle coded message
1010 coded_str = unpackCStringUtf8# coded
1013 = case (span not_bar coded_str) of { (loc, rest) ->
1015 ('|':det) -> (loc, ' ' : det)
1018 not_bar c = c /= '|'