2 {-# OPTIONS -fno-implicit-prelude #-}
3 -----------------------------------------------------------------------------
6 -- Copyright : (c) The University of Glasgow 1994-2002
7 -- License : see libraries/base/LICENSE
9 -- Maintainer : cvs-ghc@haskell.org
10 -- Stability : internal
11 -- Portability : non-portable (GHC Extensions)
13 -- Definitions for the 'IO' monad and its friends.
15 -----------------------------------------------------------------------------
17 module GHC.IOBase where
20 import GHC.Arr -- to derive Ix class
21 import GHC.Enum -- to derive Enum class
24 import GHC.Num -- To get fromInteger etc, needed because of -fno-implicit-prelude
25 import Data.Maybe ( Maybe(..) )
31 import {-# SOURCE #-} Data.Dynamic
34 -- ---------------------------------------------------------------------------
38 The IO Monad is just an instance of the ST monad, where the state is
39 the real world. We use the exception mechanism (in GHC.Exception) to
40 implement IO exceptions.
42 NOTE: The IO representation is deeply wired in to various parts of the
43 system. The following list may or may not be exhaustive:
45 Compiler - types of various primitives in PrimOp.lhs
47 RTS - forceIO (StgMiscClosures.hc)
48 - catchzh_fast, (un)?blockAsyncExceptionszh_fast, raisezh_fast
50 - raiseAsync (Schedule.c)
52 Prelude - GHC.IOBase.lhs, and several other places including
55 Libraries - parts of hslibs/lang.
61 A value of type @'IO' a@ is a computation which, when performed,
62 does some I\/O before returning a value of type @a@.
64 There is really only one way to \"perform\" an I\/O action: bind it to
65 @Main.main@ in your program. When your program is run, the I\/O will
66 be performed. It isn't possible to perform I\/O from an arbitrary
67 function, unless that function is itself in the 'IO' monad and called
68 at some point, directly or indirectly, from @Main.main@.
70 'IO' is a monad, so 'IO' actions can be combined using either the do-notation
71 or the '>>' and '>>=' operations from the 'Monad' class.
73 newtype IO a = IO (State# RealWorld -> (# State# RealWorld, a #))
75 unIO :: IO a -> (State# RealWorld -> (# State# RealWorld, a #))
78 instance Functor IO where
79 fmap f x = x >>= (return . f)
81 instance Monad IO where
85 m >> k = m >>= \ _ -> k
91 failIO :: String -> IO a
92 failIO s = ioError (userError s)
94 liftIO :: IO a -> State# RealWorld -> STret RealWorld a
95 liftIO (IO m) = \s -> case m s of (# s', r #) -> STret s' r
97 bindIO :: IO a -> (a -> IO b) -> IO b
98 bindIO (IO m) k = IO ( \ s ->
100 (# new_s, a #) -> unIO (k a) new_s
103 thenIO :: IO a -> IO b -> IO b
104 thenIO (IO m) k = IO ( \ s ->
106 (# new_s, a #) -> unIO k new_s
109 returnIO :: a -> IO a
110 returnIO x = IO (\ s -> (# s, x #))
112 -- ---------------------------------------------------------------------------
113 -- Coercions between IO and ST
115 --stToIO :: (forall s. ST s a) -> IO a
116 stToIO :: ST RealWorld a -> IO a
119 ioToST :: IO a -> ST RealWorld a
120 ioToST (IO m) = (ST m)
122 -- ---------------------------------------------------------------------------
123 -- Unsafe IO operations
126 This is the "back door" into the 'IO' monad, allowing
127 'IO' computation to be performed at any time. For
128 this to be safe, the 'IO' computation should be
129 free of side effects and independent of its environment.
131 If the I\/O computation wrapped in 'unsafePerformIO'
132 performs side effects, then the relative order in which those side
133 effects take place (relative to the main I\/O trunk, or other calls to
134 'unsafePerformIO') is indeterminate. You have to be careful when
135 writing and compiling modules that use 'unsafePerformIO':
137 * Use @{\-\# NOINLINE foo \#-\}@ as a pragma on any function @foo@
138 that calls 'unsafePerformIO'. If the call is inlined,
139 the I\/O may be performed more than once.
141 * Use the compiler flag @-fno-cse@ to prevent common sub-expression
142 elimination being performed on the module, which might combine
143 two side effects that were meant to be separate. A good example
144 is using multiple global variables (like @test@ in the example below).
146 * Make sure that the either you switch off let-floating, or that the
147 call to 'unsafePerformIO' cannot float outside a lambda. For example,
150 f x = unsafePerformIO (newIORef [])
152 you may get only one reference cell shared between all calls to @f@.
155 f x = unsafePerformIO (newIORef [x])
157 because now it can't float outside the lambda.
159 It is less well known that
160 'unsafePerformIO' is not type safe. For example:
163 > test = unsafePerformIO $ newIORef []
166 > writeIORef test [42]
167 > bang \<- readIORef test
168 > print (bang :: [Char])
170 This program will core dump. This problem with polymorphic references
171 is well known in the ML community, and does not arise with normal
172 monadic use of references. There is no easy way to make it impossible
173 once you use 'unsafePerformIO'. Indeed, it is
174 possible to write @coerce :: a -> b@ with the
175 help of 'unsafePerformIO'. So be careful!
177 {-# NOINLINE unsafePerformIO #-}
178 unsafePerformIO :: IO a -> a
179 unsafePerformIO (IO m) = case m realWorld# of (# _, r #) -> r
182 'unsafeInterleaveIO' allows 'IO' computation to be deferred lazily.
183 When passed a value of type @IO a@, the 'IO' will only be performed
184 when the value of the @a@ is demanded. This is used to implement lazy
185 file reading, see 'IO.hGetContents'.
187 {-# NOINLINE unsafeInterleaveIO #-}
188 unsafeInterleaveIO :: IO a -> IO a
189 unsafeInterleaveIO (IO m)
191 r = case m s of (# _, res #) -> res
195 -- ---------------------------------------------------------------------------
198 data MVar a = MVar (MVar# RealWorld a)
200 An 'MVar' (pronounced \"em-var\") is a synchronising variable, used
201 for communication between concurrent threads. It can be thought of
202 as a a box, which may be empty or full.
205 -- pull in Eq (Mvar a) too, to avoid GHC.Conc being an orphan-instance module
206 instance Eq (MVar a) where
207 (MVar mvar1#) == (MVar mvar2#) = sameMVar# mvar1# mvar2#
209 -- A Handle is represented by (a reference to) a record
210 -- containing the state of the I/O port/device. We record
211 -- the following pieces of info:
213 -- * type (read,write,closed etc.)
214 -- * the underlying file descriptor
216 -- * buffer, and spare buffers
217 -- * user-friendly name (usually the
218 -- FilePath used when IO.openFile was called)
220 -- Note: when a Handle is garbage collected, we want to flush its buffer
221 -- and close the OS file handle, so as to free up a (precious) resource.
224 = FileHandle -- A normal handle to a file
227 | DuplexHandle -- A handle to a read/write stream
228 !(MVar Handle__) -- The read side
229 !(MVar Handle__) -- The write side
232 -- * A 'FileHandle' is seekable. A 'DuplexHandle' may or may not be
235 instance Eq Handle where
236 (FileHandle h1) == (FileHandle h2) = h1 == h2
237 (DuplexHandle h1 _) == (DuplexHandle h2 _) = h1 == h2
240 type FD = Int -- XXX ToDo: should be CInt
244 haFD :: !FD, -- file descriptor
245 haType :: HandleType, -- type (read/write/append etc.)
246 haIsBin :: Bool, -- binary mode?
247 haIsStream :: Bool, -- is this a stream handle?
248 haBufferMode :: BufferMode, -- buffer contains read/write data?
249 haFilePath :: FilePath, -- file name, possibly
250 haBuffer :: !(IORef Buffer), -- the current buffer
251 haBuffers :: !(IORef BufferList), -- spare buffers
252 haOtherSide :: Maybe (MVar Handle__) -- ptr to the write side of a
256 -- ---------------------------------------------------------------------------
259 -- The buffer is represented by a mutable variable containing a
260 -- record, where the record contains the raw buffer and the start/end
261 -- points of the filled portion. We use a mutable variable so that
262 -- the common operation of writing (or reading) some data from (to)
263 -- the buffer doesn't need to modify, and hence copy, the handle
264 -- itself, it just updates the buffer.
266 -- There will be some allocation involved in a simple hPutChar in
267 -- order to create the new Buffer structure (below), but this is
268 -- relatively small, and this only has to be done once per write
271 -- The buffer contains its size - we could also get the size by
272 -- calling sizeOfMutableByteArray# on the raw buffer, but that tends
273 -- to be rounded up to the nearest Word.
275 type RawBuffer = MutableByteArray# RealWorld
277 -- INVARIANTS on a Buffer:
279 -- * A handle *always* has a buffer, even if it is only 1 character long
280 -- (an unbuffered handle needs a 1 character buffer in order to support
281 -- hLookAhead and hIsEOF).
283 -- * if r == w, then r == 0 && w == 0
284 -- * if state == WriteBuffer, then r == 0
285 -- * a write buffer is never full. If an operation
286 -- fills up the buffer, it will always flush it before
288 -- * a read buffer may be full as a result of hLookAhead. In normal
289 -- operation, a read buffer always has at least one character of space.
297 bufState :: BufferState
300 data BufferState = ReadBuffer | WriteBuffer deriving (Eq)
302 -- we keep a few spare buffers around in a handle to avoid allocating
303 -- a new one for each hPutStr. These buffers are *guaranteed* to be the
304 -- same size as the main buffer.
307 | BufferListCons RawBuffer BufferList
310 bufferIsWritable :: Buffer -> Bool
311 bufferIsWritable Buffer{ bufState=WriteBuffer } = True
312 bufferIsWritable _other = False
314 bufferEmpty :: Buffer -> Bool
315 bufferEmpty Buffer{ bufRPtr=r, bufWPtr=w } = r == w
317 -- only makes sense for a write buffer
318 bufferFull :: Buffer -> Bool
319 bufferFull b@Buffer{ bufWPtr=w } = w >= bufSize b
321 -- Internally, we classify handles as being one
332 isReadableHandleType ReadHandle = True
333 isReadableHandleType ReadWriteHandle = True
334 isReadableHandleType _ = False
336 isWritableHandleType AppendHandle = True
337 isWritableHandleType WriteHandle = True
338 isWritableHandleType ReadWriteHandle = True
339 isWritableHandleType _ = False
341 -- File names are specified using @FilePath@, a OS-dependent
342 -- string that (hopefully, I guess) maps to an accessible file/object.
344 type FilePath = String
346 -- ---------------------------------------------------------------------------
349 -- Three kinds of buffering are supported: line-buffering,
350 -- block-buffering or no-buffering. These modes have the following
351 -- effects. For output, items are written out from the internal
352 -- buffer according to the buffer mode:
354 -- o line-buffering the entire output buffer is written
355 -- out whenever a newline is output, the output buffer overflows,
356 -- a flush is issued, or the handle is closed.
358 -- o block-buffering the entire output buffer is written out whenever
359 -- it overflows, a flush is issued, or the handle
362 -- o no-buffering output is written immediately, and never stored
363 -- in the output buffer.
365 -- The output buffer is emptied as soon as it has been written out.
367 -- Similarly, input occurs according to the buffer mode for handle {\em hdl}.
369 -- o line-buffering when the input buffer for the handle is not empty,
370 -- the next item is obtained from the buffer;
371 -- otherwise, when the input buffer is empty,
372 -- characters up to and including the next newline
373 -- character are read into the buffer. No characters
374 -- are available until the newline character is
377 -- o block-buffering when the input buffer for the handle becomes empty,
378 -- the next block of data is read into this buffer.
380 -- o no-buffering the next input item is read and returned.
382 -- For most implementations, physical files will normally be block-buffered
383 -- and terminals will normally be line-buffered. (the IO interface provides
384 -- operations for changing the default buffering of a handle tho.)
387 = NoBuffering | LineBuffering | BlockBuffering (Maybe Int)
388 deriving (Eq, Ord, Read, Show)
390 -- ---------------------------------------------------------------------------
393 -- |A mutable variable in the 'IO' monad
394 newtype IORef a = IORef (STRef RealWorld a) deriving Eq
396 -- |Build a new 'IORef'
397 newIORef :: a -> IO (IORef a)
398 newIORef v = stToIO (newSTRef v) >>= \ var -> return (IORef var)
400 -- |Read the value of an 'IORef'
401 readIORef :: IORef a -> IO a
402 readIORef (IORef var) = stToIO (readSTRef var)
404 -- |Write a new value into an 'IORef'
405 writeIORef :: IORef a -> a -> IO ()
406 writeIORef (IORef var) v = stToIO (writeSTRef var v)
408 -- ---------------------------------------------------------------------------
409 -- Show instance for Handles
411 -- handle types are 'show'n when printing error msgs, so
412 -- we provide a more user-friendly Show instance for it
413 -- than the derived one.
415 instance Show HandleType where
418 ClosedHandle -> showString "closed"
419 SemiClosedHandle -> showString "semi-closed"
420 ReadHandle -> showString "readable"
421 WriteHandle -> showString "writable"
422 AppendHandle -> showString "writable (append)"
423 ReadWriteHandle -> showString "read-writable"
425 instance Show Handle where
426 showsPrec p (FileHandle h) = showHandle p h False
427 showsPrec p (DuplexHandle _ h) = showHandle p h True
429 showHandle p h duplex =
431 -- (Big) SIGH: unfolded defn of takeMVar to avoid
432 -- an (oh-so) unfortunate module loop with GHC.Conc.
433 hdl_ = unsafePerformIO (IO $ \ s# ->
434 case h of { MVar h# ->
435 case takeMVar# h# s# of { (# s2# , r #) ->
436 case putMVar# h# r s2# of { s3# ->
439 showType | duplex = showString "duplex (read-write)"
440 | otherwise = showsPrec p (haType hdl_)
443 showHdl (haType hdl_)
444 (showString "loc=" . showString (haFilePath hdl_) . showChar ',' .
445 showString "type=" . showType . showChar ',' .
446 showString "binary=" . showsPrec p (haIsBin hdl_) . showChar ',' .
447 showString "buffering=" . showBufMode (unsafePerformIO (readIORef (haBuffer hdl_))) (haBufferMode hdl_) . showString "}" )
450 showHdl :: HandleType -> ShowS -> ShowS
453 ClosedHandle -> showsPrec p ht . showString "}"
456 showBufMode :: Buffer -> BufferMode -> ShowS
457 showBufMode buf bmo =
459 NoBuffering -> showString "none"
460 LineBuffering -> showString "line"
461 BlockBuffering (Just n) -> showString "block " . showParen True (showsPrec p n)
462 BlockBuffering Nothing -> showString "block " . showParen True (showsPrec p def)
467 -- ------------------------------------------------------------------------
468 -- Exception datatype and operations
470 -- |The type of exceptions. Every kind of system-generated exception
471 -- has a constructor in the 'Exception' type, and values of other
472 -- types may be injected into 'Exception' by coercing them to
473 -- 'Dynamic' (see the section on Dynamic Exceptions: "Control.Exception\#DynamicExceptions").
475 -- For backwards compatibility with Haskell 98, 'IOError' is a type synonym
478 = ArithException ArithException
479 -- ^Exceptions raised by arithmetic
480 -- operations. (NOTE: GHC currently does not throw
481 -- 'ArithException's except for 'DivideByZero').
482 | ArrayException ArrayException
483 -- ^Exceptions raised by array-related
484 -- operations. (NOTE: GHC currently does not throw
485 -- 'ArrayException's).
486 | AssertionFailed String
487 -- ^This exception is thrown by the
488 -- 'assert' operation when the condition
489 -- fails. The 'String' argument contains the
490 -- location of the assertion in the source program.
491 | AsyncException AsyncException
492 -- ^Asynchronous exceptions (see section on Asynchronous Exceptions: "Control.Exception\#AsynchronousExceptions").
494 -- ^The current thread was executing a call to
495 -- 'takeMVar' that could never return, because there are no other
496 -- references to this 'MVar'.
498 -- ^There are no runnable threads, so the program is
499 -- deadlocked. The 'Deadlock' exception is
500 -- raised in the main thread only (see also: "Control.Concurrent").
501 | DynException Dynamic
502 -- ^Dynamically typed exceptions (see section on Dynamic Exceptions: "Control.Exception\#DynamicExceptions").
504 -- ^The 'ErrorCall' exception is thrown by 'error'. The 'String'
505 -- argument of 'ErrorCall' is the string passed to 'error' when it was
507 | ExitException ExitCode
508 -- ^The 'ExitException' exception is thrown by 'System.exitWith' (and
509 -- 'System.exitFailure'). The 'ExitCode' argument is the value passed
510 -- to 'System.exitWith'. An unhandled 'ExitException' exception in the
511 -- main thread will cause the program to be terminated with the given
513 | IOException IOException
514 -- ^These are the standard IO exceptions generated by
515 -- Haskell\'s @IO@ operations. See also "System.IO.Error".
516 | NoMethodError String
517 -- ^An attempt was made to invoke a class method which has
518 -- no definition in this instance, and there was no default
519 -- definition given in the class declaration. GHC issues a
520 -- warning when you compile an instance which has missing
523 -- ^The current thread is stuck in an infinite loop. This
524 -- exception may or may not be thrown when the program is
526 | PatternMatchFail String
527 -- ^A pattern matching failure. The 'String' argument should contain a
528 -- descriptive message including the function name, source file
531 -- ^An attempt was made to evaluate a field of a record
532 -- for which no value was given at construction time. The
533 -- 'String' argument gives the location of the
534 -- record construction in the source program.
536 -- ^A field selection was attempted on a constructor that
537 -- doesn\'t have the requested field. This can happen with
538 -- multi-constructor records when one or more fields are
539 -- missing from some of the constructors. The
540 -- 'String' argument gives the location of the
541 -- record selection in the source program.
543 -- ^An attempt was made to update a field in a record,
544 -- where the record doesn\'t have the requested field. This can
545 -- only occur with multi-constructor records, when one or more
546 -- fields are missing from some of the constructors. The
547 -- 'String' argument gives the location of the
548 -- record update in the source program.
550 -- |The type of arithmetic exceptions
560 -- |Asynchronous exceptions
563 -- ^The current thread\'s stack exceeded its limit.
564 -- Since an exception has been raised, the thread\'s stack
565 -- will certainly be below its limit again, but the
566 -- programmer should take remedial action
569 -- ^The program\'s heap is reaching its limit, and
570 -- the program should take action to reduce the amount of
571 -- live data it has. Notes:
573 -- * It is undefined which thread receives this exception.
575 -- * GHC currently does not throw 'HeapOverflow' exceptions.
577 -- ^This exception is raised by another thread
578 -- calling 'killThread', or by the system
579 -- if it needs to terminate the thread for some
583 -- | Exceptions generated by array operations
585 = IndexOutOfBounds String
586 -- ^An attempt was made to index an array outside
587 -- its declared bounds.
588 | UndefinedElement String
589 -- ^An attempt was made to evaluate an element of an
590 -- array that had not been initialized.
593 stackOverflow, heapOverflow :: Exception -- for the RTS
594 stackOverflow = AsyncException StackOverflow
595 heapOverflow = AsyncException HeapOverflow
597 instance Show ArithException where
598 showsPrec _ Overflow = showString "arithmetic overflow"
599 showsPrec _ Underflow = showString "arithmetic underflow"
600 showsPrec _ LossOfPrecision = showString "loss of precision"
601 showsPrec _ DivideByZero = showString "divide by zero"
602 showsPrec _ Denormal = showString "denormal"
604 instance Show AsyncException where
605 showsPrec _ StackOverflow = showString "stack overflow"
606 showsPrec _ HeapOverflow = showString "heap overflow"
607 showsPrec _ ThreadKilled = showString "thread killed"
609 instance Show ArrayException where
610 showsPrec _ (IndexOutOfBounds s)
611 = showString "array index out of range"
612 . (if not (null s) then showString ": " . showString s
614 showsPrec _ (UndefinedElement s)
615 = showString "undefined array element"
616 . (if not (null s) then showString ": " . showString s
619 instance Show Exception where
620 showsPrec _ (IOException err) = shows err
621 showsPrec _ (ArithException err) = shows err
622 showsPrec _ (ArrayException err) = shows err
623 showsPrec _ (ErrorCall err) = showString err
624 showsPrec _ (ExitException err) = showString "exit: " . shows err
625 showsPrec _ (NoMethodError err) = showString err
626 showsPrec _ (PatternMatchFail err) = showString err
627 showsPrec _ (RecSelError err) = showString err
628 showsPrec _ (RecConError err) = showString err
629 showsPrec _ (RecUpdError err) = showString err
630 showsPrec _ (AssertionFailed err) = showString err
631 showsPrec _ (DynException _err) = showString "unknown exception"
632 showsPrec _ (AsyncException e) = shows e
633 showsPrec _ (BlockedOnDeadMVar) = showString "thread blocked indefinitely"
634 showsPrec _ (NonTermination) = showString "<<loop>>"
635 showsPrec _ (Deadlock) = showString "<<deadlock>>"
637 instance Eq Exception where
638 IOException e1 == IOException e2 = e1 == e2
639 ArithException e1 == ArithException e2 = e1 == e2
640 ArrayException e1 == ArrayException e2 = e1 == e2
641 ErrorCall e1 == ErrorCall e2 = e1 == e2
642 ExitException e1 == ExitException e2 = e1 == e2
643 NoMethodError e1 == NoMethodError e2 = e1 == e2
644 PatternMatchFail e1 == PatternMatchFail e2 = e1 == e2
645 RecSelError e1 == RecSelError e2 = e1 == e2
646 RecConError e1 == RecConError e2 = e1 == e2
647 RecUpdError e1 == RecUpdError e2 = e1 == e2
648 AssertionFailed e1 == AssertionFailed e2 = e1 == e2
649 DynException _ == DynException _ = False -- incomparable
650 AsyncException e1 == AsyncException e2 = e1 == e2
651 BlockedOnDeadMVar == BlockedOnDeadMVar = True
652 NonTermination == NonTermination = True
653 Deadlock == Deadlock = True
655 -- -----------------------------------------------------------------------------
658 -- The `ExitCode' type defines the exit codes that a program
659 -- can return. `ExitSuccess' indicates successful termination;
660 -- and `ExitFailure code' indicates program failure
661 -- with value `code'. The exact interpretation of `code'
662 -- is operating-system dependent. In particular, some values of
663 -- `code' may be prohibited (e.g. 0 on a POSIX-compliant system).
665 -- We need it here because it is used in ExitException in the
666 -- Exception datatype (above).
668 data ExitCode = ExitSuccess | ExitFailure Int
669 deriving (Eq, Ord, Read, Show)
671 -- --------------------------------------------------------------------------
674 -- | Throw an exception. Exceptions may be thrown from purely
675 -- functional code, but may only be caught within the 'IO' monad.
676 throw :: Exception -> a
677 throw exception = raise# exception
679 -- | A variant of 'throw' that can be used within the 'IO' monad.
681 -- Although 'ioError' has a type that is an instance of the type of 'throw', the
682 -- two functions are subtly different:
684 -- > throw e `seq` return () ===> throw e
685 -- > ioError e `seq` return () ===> return ()
687 -- The first example will cause the exception @e@ to be raised,
688 -- whereas the second one won\'t. In fact, 'ioError' will only cause
689 -- an exception to be raised when it is used within the 'IO' monad.
690 -- The 'ioError' variant should be used in preference to 'throw' to
691 -- raise an exception within the 'IO' monad because it guarantees
692 -- ordering with respect to other 'IO' operations, whereas 'throw'
694 ioError :: Exception -> IO a
695 ioError err = IO $ \s -> throw err s
697 ioException :: IOException -> IO a
698 ioException err = IO $ \s -> throw (IOException err) s
700 -- ---------------------------------------------------------------------------
703 -- A value @IOError@ encode errors occurred in the @IO@ monad.
704 -- An @IOError@ records a more specific error type, a descriptive
705 -- string and maybe the handle that was used when the error was
708 type IOError = Exception
712 ioe_handle :: Maybe Handle, -- the handle used by the action flagging
714 ioe_type :: IOErrorType, -- what it was.
715 ioe_location :: String, -- location.
716 ioe_descr :: String, -- error type specific information.
717 ioe_filename :: Maybe FilePath -- filename the error is related to.
720 instance Eq IOException where
721 (IOError h1 e1 loc1 str1 fn1) == (IOError h2 e2 loc2 str2 fn2) =
722 e1==e2 && str1==str2 && h1==h2 && loc1==loc2 && fn1==fn2
735 | UnsatisfiedConstraints
742 | UnsupportedOperation
746 | DynIOError Dynamic -- cheap&cheerful extensible IO error type.
748 instance Eq IOErrorType where
751 DynIOError{} -> False -- from a strictness POV, compatible with a derived Eq inst?
752 _ -> getTag# x ==# getTag# y
754 instance Show IOErrorType where
758 AlreadyExists -> "already exists"
759 NoSuchThing -> "does not exist"
760 ResourceBusy -> "resource busy"
761 ResourceExhausted -> "resource exhausted"
763 IllegalOperation -> "illegal operation"
764 PermissionDenied -> "permission denied"
765 UserError -> "user error"
766 HardwareFault -> "hardware fault"
767 InappropriateType -> "inappropriate type"
768 Interrupted -> "interrupted"
769 InvalidArgument -> "invalid argument"
770 OtherError -> "failed"
771 ProtocolError -> "protocol error"
772 ResourceVanished -> "resource vanished"
773 SystemError -> "system error"
774 TimeExpired -> "timeout"
775 UnsatisfiedConstraints -> "unsatisified constraints" -- ultra-precise!
776 UnsupportedOperation -> "unsupported operation"
777 DynIOError{} -> "unknown IO error"
779 userError :: String -> IOError
780 userError str = IOException (IOError Nothing UserError "" str Nothing)
782 -- ---------------------------------------------------------------------------
785 instance Show IOException where
786 showsPrec p (IOError hdl iot loc s fn) =
790 _ -> showString "\nAction: " . showString loc) .
793 Just h -> showString "\nHandle: " . showsPrec p h) .
796 _ -> showString "\nReason: " . showString s) .
799 Just name -> showString "\nFile: " . showString name)
801 -- -----------------------------------------------------------------------------
804 data IOMode = ReadMode | WriteMode | AppendMode | ReadWriteMode
805 deriving (Eq, Ord, Ix, Enum, Read, Show)