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 'System.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
225 FilePath -- the file (invariant)
228 | DuplexHandle -- A handle to a read/write stream
229 FilePath -- file for a FIFO, otherwise some
230 -- descriptive string.
231 !(MVar Handle__) -- The read side
232 !(MVar Handle__) -- The write side
235 -- * A 'FileHandle' is seekable. A 'DuplexHandle' may or may not be
238 instance Eq Handle where
239 (FileHandle _ h1) == (FileHandle _ h2) = h1 == h2
240 (DuplexHandle _ h1 _) == (DuplexHandle _ h2 _) = h1 == h2
243 type FD = Int -- XXX ToDo: should be CInt
247 haFD :: !FD, -- file descriptor
248 haType :: HandleType, -- type (read/write/append etc.)
249 haIsBin :: Bool, -- binary mode?
250 haIsStream :: Bool, -- is this a stream handle?
251 haBufferMode :: BufferMode, -- buffer contains read/write data?
252 haBuffer :: !(IORef Buffer), -- the current buffer
253 haBuffers :: !(IORef BufferList), -- spare buffers
254 haOtherSide :: Maybe (MVar Handle__) -- ptr to the write side of a
258 -- ---------------------------------------------------------------------------
261 -- The buffer is represented by a mutable variable containing a
262 -- record, where the record contains the raw buffer and the start/end
263 -- points of the filled portion. We use a mutable variable so that
264 -- the common operation of writing (or reading) some data from (to)
265 -- the buffer doesn't need to modify, and hence copy, the handle
266 -- itself, it just updates the buffer.
268 -- There will be some allocation involved in a simple hPutChar in
269 -- order to create the new Buffer structure (below), but this is
270 -- relatively small, and this only has to be done once per write
273 -- The buffer contains its size - we could also get the size by
274 -- calling sizeOfMutableByteArray# on the raw buffer, but that tends
275 -- to be rounded up to the nearest Word.
277 type RawBuffer = MutableByteArray# RealWorld
279 -- INVARIANTS on a Buffer:
281 -- * A handle *always* has a buffer, even if it is only 1 character long
282 -- (an unbuffered handle needs a 1 character buffer in order to support
283 -- hLookAhead and hIsEOF).
285 -- * if r == w, then r == 0 && w == 0
286 -- * if state == WriteBuffer, then r == 0
287 -- * a write buffer is never full. If an operation
288 -- fills up the buffer, it will always flush it before
290 -- * a read buffer may be full as a result of hLookAhead. In normal
291 -- operation, a read buffer always has at least one character of space.
299 bufState :: BufferState
302 data BufferState = ReadBuffer | WriteBuffer deriving (Eq)
304 -- we keep a few spare buffers around in a handle to avoid allocating
305 -- a new one for each hPutStr. These buffers are *guaranteed* to be the
306 -- same size as the main buffer.
309 | BufferListCons RawBuffer BufferList
312 bufferIsWritable :: Buffer -> Bool
313 bufferIsWritable Buffer{ bufState=WriteBuffer } = True
314 bufferIsWritable _other = False
316 bufferEmpty :: Buffer -> Bool
317 bufferEmpty Buffer{ bufRPtr=r, bufWPtr=w } = r == w
319 -- only makes sense for a write buffer
320 bufferFull :: Buffer -> Bool
321 bufferFull b@Buffer{ bufWPtr=w } = w >= bufSize b
323 -- Internally, we classify handles as being one
334 isReadableHandleType ReadHandle = True
335 isReadableHandleType ReadWriteHandle = True
336 isReadableHandleType _ = False
338 isWritableHandleType AppendHandle = True
339 isWritableHandleType WriteHandle = True
340 isWritableHandleType ReadWriteHandle = True
341 isWritableHandleType _ = False
343 -- File names are specified using @FilePath@, a OS-dependent
344 -- string that (hopefully, I guess) maps to an accessible file/object.
346 type FilePath = String
348 -- ---------------------------------------------------------------------------
351 -- Three kinds of buffering are supported: line-buffering,
352 -- block-buffering or no-buffering. These modes have the following
353 -- effects. For output, items are written out from the internal
354 -- buffer according to the buffer mode:
356 -- o line-buffering the entire output buffer is written
357 -- out whenever a newline is output, the output buffer overflows,
358 -- a flush is issued, or the handle is closed.
360 -- o block-buffering the entire output buffer is written out whenever
361 -- it overflows, a flush is issued, or the handle
364 -- o no-buffering output is written immediately, and never stored
365 -- in the output buffer.
367 -- The output buffer is emptied as soon as it has been written out.
369 -- Similarly, input occurs according to the buffer mode for handle {\em hdl}.
371 -- o line-buffering when the input buffer for the handle is not empty,
372 -- the next item is obtained from the buffer;
373 -- otherwise, when the input buffer is empty,
374 -- characters up to and including the next newline
375 -- character are read into the buffer. No characters
376 -- are available until the newline character is
379 -- o block-buffering when the input buffer for the handle becomes empty,
380 -- the next block of data is read into this buffer.
382 -- o no-buffering the next input item is read and returned.
384 -- For most implementations, physical files will normally be block-buffered
385 -- and terminals will normally be line-buffered. (the IO interface provides
386 -- operations for changing the default buffering of a handle tho.)
389 = NoBuffering | LineBuffering | BlockBuffering (Maybe Int)
390 deriving (Eq, Ord, Read, Show)
392 -- ---------------------------------------------------------------------------
395 -- |A mutable variable in the 'IO' monad
396 newtype IORef a = IORef (STRef RealWorld a)
398 -- explicit instance because Haddock can't figure out a derived one
399 instance Eq (IORef a) where
400 IORef x == IORef y = x == y
402 -- |Build a new 'IORef'
403 newIORef :: a -> IO (IORef a)
404 newIORef v = stToIO (newSTRef v) >>= \ var -> return (IORef var)
406 -- |Read the value of an 'IORef'
407 readIORef :: IORef a -> IO a
408 readIORef (IORef var) = stToIO (readSTRef var)
410 -- |Write a new value into an 'IORef'
411 writeIORef :: IORef a -> a -> IO ()
412 writeIORef (IORef var) v = stToIO (writeSTRef var v)
414 -- ---------------------------------------------------------------------------
415 -- | An 'IOArray' is a mutable, boxed, non-strict array in the 'IO' monad.
416 -- The type arguments are as follows:
418 -- * @i@: the index type of the array (should be an instance of 'Ix')
420 -- * @e@: the element type of the array.
424 newtype IOArray i e = IOArray (STArray RealWorld i e)
426 -- explicit instance because Haddock can't figure out a derived one
427 instance Eq (IOArray i e) where
428 IOArray x == IOArray y = x == y
430 -- |Build a new 'IOArray'
431 newIOArray :: Ix i => (i,i) -> e -> IO (IOArray i e)
432 {-# INLINE newIOArray #-}
433 newIOArray lu init = stToIO $ do {marr <- newSTArray lu init; return (IOArray marr)}
435 -- | Read a value from an 'IOArray'
436 unsafeReadIOArray :: Ix i => IOArray i e -> Int -> IO e
437 {-# INLINE unsafeReadIOArray #-}
438 unsafeReadIOArray (IOArray marr) i = stToIO (unsafeReadSTArray marr i)
440 -- | Write a new value into an 'IOArray'
441 unsafeWriteIOArray :: Ix i => IOArray i e -> Int -> e -> IO ()
442 {-# INLINE unsafeWriteIOArray #-}
443 unsafeWriteIOArray (IOArray marr) i e = stToIO (unsafeWriteSTArray marr i e)
445 -- | Read a value from an 'IOArray'
446 readIOArray :: Ix i => IOArray i e -> i -> IO e
447 readIOArray (IOArray marr) i = stToIO (readSTArray marr i)
449 -- | Write a new value into an 'IOArray'
450 writeIOArray :: Ix i => IOArray i e -> i -> e -> IO ()
451 writeIOArray (IOArray marr) i e = stToIO (writeSTArray marr i e)
454 -- ---------------------------------------------------------------------------
455 -- Show instance for Handles
457 -- handle types are 'show'n when printing error msgs, so
458 -- we provide a more user-friendly Show instance for it
459 -- than the derived one.
461 instance Show HandleType where
464 ClosedHandle -> showString "closed"
465 SemiClosedHandle -> showString "semi-closed"
466 ReadHandle -> showString "readable"
467 WriteHandle -> showString "writable"
468 AppendHandle -> showString "writable (append)"
469 ReadWriteHandle -> showString "read-writable"
471 instance Show Handle where
472 showsPrec p (FileHandle file _) = showHandle file
473 showsPrec p (DuplexHandle file _ _) = showHandle file
475 showHandle file = showString "{handle: " . showString file . showString "}"
477 -- ------------------------------------------------------------------------
478 -- Exception datatype and operations
480 -- |The type of exceptions. Every kind of system-generated exception
481 -- has a constructor in the 'Exception' type, and values of other
482 -- types may be injected into 'Exception' by coercing them to
483 -- 'Dynamic' (see the section on Dynamic Exceptions: "Control.Exception\#DynamicExceptions").
485 = ArithException ArithException
486 -- ^Exceptions raised by arithmetic
487 -- operations. (NOTE: GHC currently does not throw
488 -- 'ArithException's except for 'DivideByZero').
489 | ArrayException ArrayException
490 -- ^Exceptions raised by array-related
491 -- operations. (NOTE: GHC currently does not throw
492 -- 'ArrayException's).
493 | AssertionFailed String
494 -- ^This exception is thrown by the
495 -- 'assert' operation when the condition
496 -- fails. The 'String' argument contains the
497 -- location of the assertion in the source program.
498 | AsyncException AsyncException
499 -- ^Asynchronous exceptions (see section on Asynchronous Exceptions: "Control.Exception\#AsynchronousExceptions").
501 -- ^The current thread was executing a call to
502 -- 'takeMVar' that could never return, because there are no other
503 -- references to this 'MVar'.
505 -- ^There are no runnable threads, so the program is
506 -- deadlocked. The 'Deadlock' exception is
507 -- raised in the main thread only (see also: "Control.Concurrent").
508 | DynException Dynamic
509 -- ^Dynamically typed exceptions (see section on Dynamic Exceptions: "Control.Exception\#DynamicExceptions").
511 -- ^The 'ErrorCall' exception is thrown by 'error'. The 'String'
512 -- argument of 'ErrorCall' is the string passed to 'error' when it was
514 | ExitException ExitCode
515 -- ^The 'ExitException' exception is thrown by 'System.Exit.exitWith' (and
516 -- 'System.Exit.exitFailure'). The 'ExitCode' argument is the value passed
517 -- to 'System.exitWith'. An unhandled 'ExitException' exception in the
518 -- main thread will cause the program to be terminated with the given
520 | IOException IOException
521 -- ^These are the standard IO exceptions generated by
522 -- Haskell\'s @IO@ operations. See also "System.IO.Error".
523 | NoMethodError String
524 -- ^An attempt was made to invoke a class method which has
525 -- no definition in this instance, and there was no default
526 -- definition given in the class declaration. GHC issues a
527 -- warning when you compile an instance which has missing
530 -- ^The current thread is stuck in an infinite loop. This
531 -- exception may or may not be thrown when the program is
533 | PatternMatchFail String
534 -- ^A pattern matching failure. The 'String' argument should contain a
535 -- descriptive message including the function name, source file
538 -- ^An attempt was made to evaluate a field of a record
539 -- for which no value was given at construction time. The
540 -- 'String' argument gives the location of the
541 -- record construction in the source program.
543 -- ^A field selection was attempted on a constructor that
544 -- doesn\'t have the requested field. This can happen with
545 -- multi-constructor records when one or more fields are
546 -- missing from some of the constructors. The
547 -- 'String' argument gives the location of the
548 -- record selection in the source program.
550 -- ^An attempt was made to update a field in a record,
551 -- where the record doesn\'t have the requested field. This can
552 -- only occur with multi-constructor records, when one or more
553 -- fields are missing from some of the constructors. The
554 -- 'String' argument gives the location of the
555 -- record update in the source program.
557 -- |The type of arithmetic exceptions
567 -- |Asynchronous exceptions
570 -- ^The current thread\'s stack exceeded its limit.
571 -- Since an exception has been raised, the thread\'s stack
572 -- will certainly be below its limit again, but the
573 -- programmer should take remedial action
576 -- ^The program\'s heap is reaching its limit, and
577 -- the program should take action to reduce the amount of
578 -- live data it has. Notes:
580 -- * It is undefined which thread receives this exception.
582 -- * GHC currently does not throw 'HeapOverflow' exceptions.
584 -- ^This exception is raised by another thread
585 -- calling 'killThread', or by the system
586 -- if it needs to terminate the thread for some
590 -- | Exceptions generated by array operations
592 = IndexOutOfBounds String
593 -- ^An attempt was made to index an array outside
594 -- its declared bounds.
595 | UndefinedElement String
596 -- ^An attempt was made to evaluate an element of an
597 -- array that had not been initialized.
600 stackOverflow, heapOverflow :: Exception -- for the RTS
601 stackOverflow = AsyncException StackOverflow
602 heapOverflow = AsyncException HeapOverflow
604 instance Show ArithException where
605 showsPrec _ Overflow = showString "arithmetic overflow"
606 showsPrec _ Underflow = showString "arithmetic underflow"
607 showsPrec _ LossOfPrecision = showString "loss of precision"
608 showsPrec _ DivideByZero = showString "divide by zero"
609 showsPrec _ Denormal = showString "denormal"
611 instance Show AsyncException where
612 showsPrec _ StackOverflow = showString "stack overflow"
613 showsPrec _ HeapOverflow = showString "heap overflow"
614 showsPrec _ ThreadKilled = showString "thread killed"
616 instance Show ArrayException where
617 showsPrec _ (IndexOutOfBounds s)
618 = showString "array index out of range"
619 . (if not (null s) then showString ": " . showString s
621 showsPrec _ (UndefinedElement s)
622 = showString "undefined array element"
623 . (if not (null s) then showString ": " . showString s
626 instance Show Exception where
627 showsPrec _ (IOException err) = shows err
628 showsPrec _ (ArithException err) = shows err
629 showsPrec _ (ArrayException err) = shows err
630 showsPrec _ (ErrorCall err) = showString err
631 showsPrec _ (ExitException err) = showString "exit: " . shows err
632 showsPrec _ (NoMethodError err) = showString err
633 showsPrec _ (PatternMatchFail err) = showString err
634 showsPrec _ (RecSelError err) = showString err
635 showsPrec _ (RecConError err) = showString err
636 showsPrec _ (RecUpdError err) = showString err
637 showsPrec _ (AssertionFailed err) = showString err
638 showsPrec _ (DynException _err) = showString "unknown exception"
639 showsPrec _ (AsyncException e) = shows e
640 showsPrec _ (BlockedOnDeadMVar) = showString "thread blocked indefinitely"
641 showsPrec _ (NonTermination) = showString "<<loop>>"
642 showsPrec _ (Deadlock) = showString "<<deadlock>>"
644 instance Eq Exception where
645 IOException e1 == IOException e2 = e1 == e2
646 ArithException e1 == ArithException e2 = e1 == e2
647 ArrayException e1 == ArrayException e2 = e1 == e2
648 ErrorCall e1 == ErrorCall e2 = e1 == e2
649 ExitException e1 == ExitException e2 = e1 == e2
650 NoMethodError e1 == NoMethodError e2 = e1 == e2
651 PatternMatchFail e1 == PatternMatchFail e2 = e1 == e2
652 RecSelError e1 == RecSelError e2 = e1 == e2
653 RecConError e1 == RecConError e2 = e1 == e2
654 RecUpdError e1 == RecUpdError e2 = e1 == e2
655 AssertionFailed e1 == AssertionFailed e2 = e1 == e2
656 DynException _ == DynException _ = False -- incomparable
657 AsyncException e1 == AsyncException e2 = e1 == e2
658 BlockedOnDeadMVar == BlockedOnDeadMVar = True
659 NonTermination == NonTermination = True
660 Deadlock == Deadlock = True
663 -- -----------------------------------------------------------------------------
666 -- The `ExitCode' type defines the exit codes that a program
667 -- can return. `ExitSuccess' indicates successful termination;
668 -- and `ExitFailure code' indicates program failure
669 -- with value `code'. The exact interpretation of `code'
670 -- is operating-system dependent. In particular, some values of
671 -- `code' may be prohibited (e.g. 0 on a POSIX-compliant system).
673 -- We need it here because it is used in ExitException in the
674 -- Exception datatype (above).
676 data ExitCode = ExitSuccess | ExitFailure Int
677 deriving (Eq, Ord, Read, Show)
679 -- --------------------------------------------------------------------------
682 -- | Throw an exception. Exceptions may be thrown from purely
683 -- functional code, but may only be caught within the 'IO' monad.
684 throw :: Exception -> a
685 throw exception = raise# exception
687 -- | A variant of 'throw' that can be used within the 'IO' monad.
689 -- Although 'throwIO' has a type that is an instance of the type of 'throw', the
690 -- two functions are subtly different:
692 -- > throw e `seq` return () ===> throw e
693 -- > throwIO e `seq` return () ===> return ()
695 -- The first example will cause the exception @e@ to be raised,
696 -- whereas the second one won\'t. In fact, 'throwIO' will only cause
697 -- an exception to be raised when it is used within the 'IO' monad.
698 -- The 'throwIO' variant should be used in preference to 'throw' to
699 -- raise an exception within the 'IO' monad because it guarantees
700 -- ordering with respect to other 'IO' operations, whereas 'throw'
702 throwIO :: Exception -> IO a
703 throwIO err = IO $ raiseIO# err
705 ioException :: IOException -> IO a
706 ioException err = IO $ raiseIO# (IOException err)
708 ioError :: IOError -> IO a
709 ioError = ioException
711 -- ---------------------------------------------------------------------------
714 -- | The Haskell 98 type for exceptions in the @IO@ monad.
715 -- In Haskell 98, this is an opaque type.
716 type IOError = IOException
718 -- |Exceptions that occur in the @IO@ monad.
719 -- An @IOException@ records a more specific error type, a descriptive
720 -- string and maybe the handle that was used when the error was
724 ioe_handle :: Maybe Handle, -- the handle used by the action flagging
726 ioe_type :: IOErrorType, -- what it was.
727 ioe_location :: String, -- location.
728 ioe_description :: String, -- error type specific information.
729 ioe_filename :: Maybe FilePath -- filename the error is related to.
732 instance Eq IOException where
733 (IOError h1 e1 loc1 str1 fn1) == (IOError h2 e2 loc2 str2 fn2) =
734 e1==e2 && str1==str2 && h1==h2 && loc1==loc2 && fn1==fn2
747 | UnsatisfiedConstraints
754 | UnsupportedOperation
758 | DynIOError Dynamic -- cheap&cheerful extensible IO error type.
760 instance Eq IOErrorType where
763 DynIOError{} -> False -- from a strictness POV, compatible with a derived Eq inst?
764 _ -> getTag x ==# getTag y
766 instance Show IOErrorType where
770 AlreadyExists -> "already exists"
771 NoSuchThing -> "does not exist"
772 ResourceBusy -> "resource busy"
773 ResourceExhausted -> "resource exhausted"
775 IllegalOperation -> "illegal operation"
776 PermissionDenied -> "permission denied"
777 UserError -> "user error"
778 HardwareFault -> "hardware fault"
779 InappropriateType -> "inappropriate type"
780 Interrupted -> "interrupted"
781 InvalidArgument -> "invalid argument"
782 OtherError -> "failed"
783 ProtocolError -> "protocol error"
784 ResourceVanished -> "resource vanished"
785 SystemError -> "system error"
786 TimeExpired -> "timeout"
787 UnsatisfiedConstraints -> "unsatisified constraints" -- ultra-precise!
788 UnsupportedOperation -> "unsupported operation"
789 DynIOError{} -> "unknown IO error"
791 userError :: String -> IOError
792 userError str = IOError Nothing UserError "" str Nothing
794 -- ---------------------------------------------------------------------------
797 instance Show IOException where
798 showsPrec p (IOError hdl iot loc s fn) =
800 Nothing -> case hdl of
802 Just h -> showsPrec p h . showString ": "
803 Just name -> showString name . showString ": ") .
806 _ -> showString loc . showString ": ") .
810 _ -> showString " (" . showString s . showString ")")
812 -- -----------------------------------------------------------------------------
815 data IOMode = ReadMode | WriteMode | AppendMode | ReadWriteMode
816 deriving (Eq, Ord, Ix, Enum, Read, Show)