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
22 import GHC.Num -- To get fromInteger etc, needed because of -fno-implicit-prelude
23 import Data.Maybe ( Maybe(..) )
29 import {-# SOURCE #-} Data.Dynamic
32 -- ---------------------------------------------------------------------------
36 The IO Monad is just an instance of the ST monad, where the state is
37 the real world. We use the exception mechanism (in GHC.Exception) to
38 implement IO exceptions.
40 NOTE: The IO representation is deeply wired in to various parts of the
41 system. The following list may or may not be exhaustive:
43 Compiler - types of various primitives in PrimOp.lhs
45 RTS - forceIO (StgMiscClosures.hc)
46 - catchzh_fast, (un)?blockAsyncExceptionszh_fast, raisezh_fast
48 - raiseAsync (Schedule.c)
50 Prelude - GHC.IOBase.lhs, and several other places including
53 Libraries - parts of hslibs/lang.
58 newtype IO a = IO (State# RealWorld -> (# State# RealWorld, a #))
60 unIO :: IO a -> (State# RealWorld -> (# State# RealWorld, a #))
63 instance Functor IO where
64 fmap f x = x >>= (return . f)
66 instance Monad IO where
70 m >> k = m >>= \ _ -> k
76 failIO :: String -> IO a
77 failIO s = ioError (userError s)
79 liftIO :: IO a -> State# RealWorld -> STret RealWorld a
80 liftIO (IO m) = \s -> case m s of (# s', r #) -> STret s' r
82 bindIO :: IO a -> (a -> IO b) -> IO b
83 bindIO (IO m) k = IO ( \ s ->
85 (# new_s, a #) -> unIO (k a) new_s
88 thenIO :: IO a -> IO b -> IO b
89 thenIO (IO m) k = IO ( \ s ->
91 (# new_s, a #) -> unIO k new_s
95 returnIO x = IO (\ s -> (# s, x #))
97 -- ---------------------------------------------------------------------------
98 -- Coercions between IO and ST
100 --stToIO :: (forall s. ST s a) -> IO a
101 stToIO :: ST RealWorld a -> IO a
104 ioToST :: IO a -> ST RealWorld a
105 ioToST (IO m) = (ST m)
107 -- ---------------------------------------------------------------------------
108 -- Unsafe IO operations
110 {-# NOINLINE unsafePerformIO #-}
111 unsafePerformIO :: IO a -> a
112 unsafePerformIO (IO m) = case m realWorld# of (# _, r #) -> r
114 {-# NOINLINE unsafeInterleaveIO #-}
115 unsafeInterleaveIO :: IO a -> IO a
116 unsafeInterleaveIO (IO m)
118 r = case m s of (# _, res #) -> res
122 -- ---------------------------------------------------------------------------
125 data MVar a = MVar (MVar# RealWorld a)
127 An 'MVar' (pronounced \"em-var\") is a synchronising variable, used
128 for communication between concurrent threads. It can be thought of
129 as a a box, which may be empty or full.
132 -- pull in Eq (Mvar a) too, to avoid GHC.Conc being an orphan-instance module
133 instance Eq (MVar a) where
134 (MVar mvar1#) == (MVar mvar2#) = sameMVar# mvar1# mvar2#
136 -- A Handle is represented by (a reference to) a record
137 -- containing the state of the I/O port/device. We record
138 -- the following pieces of info:
140 -- * type (read,write,closed etc.)
141 -- * the underlying file descriptor
143 -- * buffer, and spare buffers
144 -- * user-friendly name (usually the
145 -- FilePath used when IO.openFile was called)
147 -- Note: when a Handle is garbage collected, we want to flush its buffer
148 -- and close the OS file handle, so as to free up a (precious) resource.
151 = FileHandle -- A normal handle to a file
154 | DuplexHandle -- A handle to a read/write stream
155 !(MVar Handle__) -- The read side
156 !(MVar Handle__) -- The write side
159 -- * A 'FileHandle' is seekable. A 'DuplexHandle' may or may not be
162 instance Eq Handle where
163 (FileHandle h1) == (FileHandle h2) = h1 == h2
164 (DuplexHandle h1 _) == (DuplexHandle h2 _) = h1 == h2
167 type FD = Int -- XXX ToDo: should be CInt
171 haFD :: !FD, -- file descriptor
172 haType :: HandleType, -- type (read/write/append etc.)
173 haIsBin :: Bool, -- binary mode?
174 haIsStream :: Bool, -- is this a stream handle?
175 haBufferMode :: BufferMode, -- buffer contains read/write data?
176 haFilePath :: FilePath, -- file name, possibly
177 haBuffer :: !(IORef Buffer), -- the current buffer
178 haBuffers :: !(IORef BufferList), -- spare buffers
179 haOtherSide :: Maybe (MVar Handle__) -- ptr to the write side of a
183 -- ---------------------------------------------------------------------------
186 -- The buffer is represented by a mutable variable containing a
187 -- record, where the record contains the raw buffer and the start/end
188 -- points of the filled portion. We use a mutable variable so that
189 -- the common operation of writing (or reading) some data from (to)
190 -- the buffer doesn't need to modify, and hence copy, the handle
191 -- itself, it just updates the buffer.
193 -- There will be some allocation involved in a simple hPutChar in
194 -- order to create the new Buffer structure (below), but this is
195 -- relatively small, and this only has to be done once per write
198 -- The buffer contains its size - we could also get the size by
199 -- calling sizeOfMutableByteArray# on the raw buffer, but that tends
200 -- to be rounded up to the nearest Word.
202 type RawBuffer = MutableByteArray# RealWorld
204 -- INVARIANTS on a Buffer:
206 -- * A handle *always* has a buffer, even if it is only 1 character long
207 -- (an unbuffered handle needs a 1 character buffer in order to support
208 -- hLookAhead and hIsEOF).
210 -- * if r == w, then r == 0 && w == 0
211 -- * if state == WriteBuffer, then r == 0
212 -- * a write buffer is never full. If an operation
213 -- fills up the buffer, it will always flush it before
215 -- * a read buffer may be full as a result of hLookAhead. In normal
216 -- operation, a read buffer always has at least one character of space.
224 bufState :: BufferState
227 data BufferState = ReadBuffer | WriteBuffer deriving (Eq)
229 -- we keep a few spare buffers around in a handle to avoid allocating
230 -- a new one for each hPutStr. These buffers are *guaranteed* to be the
231 -- same size as the main buffer.
234 | BufferListCons RawBuffer BufferList
237 bufferIsWritable :: Buffer -> Bool
238 bufferIsWritable Buffer{ bufState=WriteBuffer } = True
239 bufferIsWritable _other = False
241 bufferEmpty :: Buffer -> Bool
242 bufferEmpty Buffer{ bufRPtr=r, bufWPtr=w } = r == w
244 -- only makes sense for a write buffer
245 bufferFull :: Buffer -> Bool
246 bufferFull b@Buffer{ bufWPtr=w } = w >= bufSize b
248 -- Internally, we classify handles as being one
259 isReadableHandleType ReadHandle = True
260 isReadableHandleType ReadWriteHandle = True
261 isReadableHandleType _ = False
263 isWritableHandleType AppendHandle = True
264 isWritableHandleType WriteHandle = True
265 isWritableHandleType ReadWriteHandle = True
266 isWritableHandleType _ = False
268 -- File names are specified using @FilePath@, a OS-dependent
269 -- string that (hopefully, I guess) maps to an accessible file/object.
271 type FilePath = String
273 -- ---------------------------------------------------------------------------
276 -- Three kinds of buffering are supported: line-buffering,
277 -- block-buffering or no-buffering. These modes have the following
278 -- effects. For output, items are written out from the internal
279 -- buffer according to the buffer mode:
281 -- o line-buffering the entire output buffer is written
282 -- out whenever a newline is output, the output buffer overflows,
283 -- a flush is issued, or the handle is closed.
285 -- o block-buffering the entire output buffer is written out whenever
286 -- it overflows, a flush is issued, or the handle
289 -- o no-buffering output is written immediately, and never stored
290 -- in the output buffer.
292 -- The output buffer is emptied as soon as it has been written out.
294 -- Similarly, input occurs according to the buffer mode for handle {\em hdl}.
296 -- o line-buffering when the input buffer for the handle is not empty,
297 -- the next item is obtained from the buffer;
298 -- otherwise, when the input buffer is empty,
299 -- characters up to and including the next newline
300 -- character are read into the buffer. No characters
301 -- are available until the newline character is
304 -- o block-buffering when the input buffer for the handle becomes empty,
305 -- the next block of data is read into this buffer.
307 -- o no-buffering the next input item is read and returned.
309 -- For most implementations, physical files will normally be block-buffered
310 -- and terminals will normally be line-buffered. (the IO interface provides
311 -- operations for changing the default buffering of a handle tho.)
314 = NoBuffering | LineBuffering | BlockBuffering (Maybe Int)
315 deriving (Eq, Ord, Read, Show)
317 -- ---------------------------------------------------------------------------
320 newtype IORef a = IORef (STRef RealWorld a) deriving Eq
322 newIORef :: a -> IO (IORef a)
323 newIORef v = stToIO (newSTRef v) >>= \ var -> return (IORef var)
325 readIORef :: IORef a -> IO a
326 readIORef (IORef var) = stToIO (readSTRef var)
328 writeIORef :: IORef a -> a -> IO ()
329 writeIORef (IORef var) v = stToIO (writeSTRef var v)
331 -- ---------------------------------------------------------------------------
332 -- Show instance for Handles
334 -- handle types are 'show'n when printing error msgs, so
335 -- we provide a more user-friendly Show instance for it
336 -- than the derived one.
338 instance Show HandleType where
341 ClosedHandle -> showString "closed"
342 SemiClosedHandle -> showString "semi-closed"
343 ReadHandle -> showString "readable"
344 WriteHandle -> showString "writable"
345 AppendHandle -> showString "writable (append)"
346 ReadWriteHandle -> showString "read-writable"
348 instance Show Handle where
349 showsPrec p (FileHandle h) = showHandle p h False
350 showsPrec p (DuplexHandle _ h) = showHandle p h True
352 showHandle p h duplex =
354 -- (Big) SIGH: unfolded defn of takeMVar to avoid
355 -- an (oh-so) unfortunate module loop with GHC.Conc.
356 hdl_ = unsafePerformIO (IO $ \ s# ->
357 case h of { MVar h# ->
358 case takeMVar# h# s# of { (# s2# , r #) ->
359 case putMVar# h# r s2# of { s3# ->
362 showType | duplex = showString "duplex (read-write)"
363 | otherwise = showsPrec p (haType hdl_)
366 showHdl (haType hdl_)
367 (showString "loc=" . showString (haFilePath hdl_) . showChar ',' .
368 showString "type=" . showType . showChar ',' .
369 showString "binary=" . showsPrec p (haIsBin hdl_) . showChar ',' .
370 showString "buffering=" . showBufMode (unsafePerformIO (readIORef (haBuffer hdl_))) (haBufferMode hdl_) . showString "}" )
373 showHdl :: HandleType -> ShowS -> ShowS
376 ClosedHandle -> showsPrec p ht . showString "}"
379 showBufMode :: Buffer -> BufferMode -> ShowS
380 showBufMode buf bmo =
382 NoBuffering -> showString "none"
383 LineBuffering -> showString "line"
384 BlockBuffering (Just n) -> showString "block " . showParen True (showsPrec p n)
385 BlockBuffering Nothing -> showString "block " . showParen True (showsPrec p def)
390 -- ------------------------------------------------------------------------
391 -- Exception datatype and operations
394 = IOException IOException -- IO exceptions
395 | ArithException ArithException -- Arithmetic exceptions
396 | ArrayException ArrayException -- Array-related exceptions
397 | ErrorCall String -- Calls to 'error'
398 | ExitException ExitCode -- Call to System.exitWith
399 | NoMethodError String -- A non-existent method was invoked
400 | PatternMatchFail String -- A pattern match / guard failure
401 | RecSelError String -- Selecting a non-existent field
402 | RecConError String -- Field missing in record construction
403 | RecUpdError String -- Record doesn't contain updated field
404 | AssertionFailed String -- Assertions
405 | DynException Dynamic -- Dynamic exceptions
406 | AsyncException AsyncException -- Externally generated errors
407 | BlockedOnDeadMVar -- Blocking on a dead MVar
408 | Deadlock -- no threads can run (raised in main thread)
426 = IndexOutOfBounds String -- out-of-range array access
427 | UndefinedElement String -- evaluating an undefined element
430 stackOverflow, heapOverflow :: Exception -- for the RTS
431 stackOverflow = AsyncException StackOverflow
432 heapOverflow = AsyncException HeapOverflow
434 instance Show ArithException where
435 showsPrec _ Overflow = showString "arithmetic overflow"
436 showsPrec _ Underflow = showString "arithmetic underflow"
437 showsPrec _ LossOfPrecision = showString "loss of precision"
438 showsPrec _ DivideByZero = showString "divide by zero"
439 showsPrec _ Denormal = showString "denormal"
441 instance Show AsyncException where
442 showsPrec _ StackOverflow = showString "stack overflow"
443 showsPrec _ HeapOverflow = showString "heap overflow"
444 showsPrec _ ThreadKilled = showString "thread killed"
446 instance Show ArrayException where
447 showsPrec _ (IndexOutOfBounds s)
448 = showString "array index out of range"
449 . (if not (null s) then showString ": " . showString s
451 showsPrec _ (UndefinedElement s)
452 = showString "undefined array element"
453 . (if not (null s) then showString ": " . showString s
456 instance Show Exception where
457 showsPrec _ (IOException err) = shows err
458 showsPrec _ (ArithException err) = shows err
459 showsPrec _ (ArrayException err) = shows err
460 showsPrec _ (ErrorCall err) = showString err
461 showsPrec _ (ExitException err) = showString "exit: " . shows err
462 showsPrec _ (NoMethodError err) = showString err
463 showsPrec _ (PatternMatchFail err) = showString err
464 showsPrec _ (RecSelError err) = showString err
465 showsPrec _ (RecConError err) = showString err
466 showsPrec _ (RecUpdError err) = showString err
467 showsPrec _ (AssertionFailed err) = showString err
468 showsPrec _ (DynException _err) = showString "unknown exception"
469 showsPrec _ (AsyncException e) = shows e
470 showsPrec _ (BlockedOnDeadMVar) = showString "thread blocked indefinitely"
471 showsPrec _ (NonTermination) = showString "<<loop>>"
472 showsPrec _ (Deadlock) = showString "<<deadlock>>"
474 instance Eq Exception where
475 IOException e1 == IOException e2 = e1 == e2
476 ArithException e1 == ArithException e2 = e1 == e2
477 ArrayException e1 == ArrayException e2 = e1 == e2
478 ErrorCall e1 == ErrorCall e2 = e1 == e2
479 ExitException e1 == ExitException e2 = e1 == e2
480 NoMethodError e1 == NoMethodError e2 = e1 == e2
481 PatternMatchFail e1 == PatternMatchFail e2 = e1 == e2
482 RecSelError e1 == RecSelError e2 = e1 == e2
483 RecConError e1 == RecConError e2 = e1 == e2
484 RecUpdError e1 == RecUpdError e2 = e1 == e2
485 AssertionFailed e1 == AssertionFailed e2 = e1 == e2
486 DynException _ == DynException _ = False -- incomparable
487 AsyncException e1 == AsyncException e2 = e1 == e2
488 BlockedOnDeadMVar == BlockedOnDeadMVar = True
489 NonTermination == NonTermination = True
490 Deadlock == Deadlock = True
492 -- -----------------------------------------------------------------------------
495 -- The `ExitCode' type defines the exit codes that a program
496 -- can return. `ExitSuccess' indicates successful termination;
497 -- and `ExitFailure code' indicates program failure
498 -- with value `code'. The exact interpretation of `code'
499 -- is operating-system dependent. In particular, some values of
500 -- `code' may be prohibited (e.g. 0 on a POSIX-compliant system).
502 -- We need it here because it is used in ExitException in the
503 -- Exception datatype (above).
505 data ExitCode = ExitSuccess | ExitFailure Int
506 deriving (Eq, Ord, Read, Show)
508 -- --------------------------------------------------------------------------
511 throw :: Exception -> a
512 throw exception = raise# exception
514 ioError :: Exception -> IO a
515 ioError err = IO $ \s -> throw err s
517 ioException :: IOException -> IO a
518 ioException err = IO $ \s -> throw (IOException err) s
520 -- ---------------------------------------------------------------------------
523 -- A value @IOError@ encode errors occurred in the @IO@ monad.
524 -- An @IOError@ records a more specific error type, a descriptive
525 -- string and maybe the handle that was used when the error was
528 type IOError = Exception
532 ioe_handle :: Maybe Handle, -- the handle used by the action flagging
534 ioe_type :: IOErrorType, -- what it was.
535 ioe_location :: String, -- location.
536 ioe_descr :: String, -- error type specific information.
537 ioe_filename :: Maybe FilePath -- filename the error is related to.
540 instance Eq IOException where
541 (IOError h1 e1 loc1 str1 fn1) == (IOError h2 e2 loc2 str2 fn2) =
542 e1==e2 && str1==str2 && h1==h2 && loc1==loc2 && fn1==fn2
555 | UnsatisfiedConstraints
562 | UnsupportedOperation
566 | DynIOError Dynamic -- cheap&cheerful extensible IO error type.
568 instance Eq IOErrorType where
571 DynIOError{} -> False -- from a strictness POV, compatible with a derived Eq inst?
572 _ -> getTag# x ==# getTag# y
574 instance Show IOErrorType where
578 AlreadyExists -> "already exists"
579 NoSuchThing -> "does not exist"
580 ResourceBusy -> "resource busy"
581 ResourceExhausted -> "resource exhausted"
583 IllegalOperation -> "illegal operation"
584 PermissionDenied -> "permission denied"
585 UserError -> "user error"
586 HardwareFault -> "hardware fault"
587 InappropriateType -> "inappropriate type"
588 Interrupted -> "interrupted"
589 InvalidArgument -> "invalid argument"
590 OtherError -> "failed"
591 ProtocolError -> "protocol error"
592 ResourceVanished -> "resource vanished"
593 SystemError -> "system error"
594 TimeExpired -> "timeout"
595 UnsatisfiedConstraints -> "unsatisified constraints" -- ultra-precise!
596 UnsupportedOperation -> "unsupported operation"
597 DynIOError{} -> "unknown IO error"
599 userError :: String -> IOError
600 userError str = IOException (IOError Nothing UserError "" str Nothing)
602 -- ---------------------------------------------------------------------------
605 instance Show IOException where
606 showsPrec p (IOError hdl iot loc s fn) =
610 _ -> showString "\nAction: " . showString loc) .
613 Just h -> showString "\nHandle: " . showsPrec p h) .
616 _ -> showString "\nReason: " . showString s) .
619 Just name -> showString "\nFile: " . showString name)