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 -- |A mutable variable in the 'IO' monad
321 newtype IORef a = IORef (STRef RealWorld a) deriving Eq
323 -- |Build a new 'IORef'
324 newIORef :: a -> IO (IORef a)
325 newIORef v = stToIO (newSTRef v) >>= \ var -> return (IORef var)
327 -- |Read the value of an 'IORef'
328 readIORef :: IORef a -> IO a
329 readIORef (IORef var) = stToIO (readSTRef var)
331 -- |Write a new value into an 'IORef'
332 writeIORef :: IORef a -> a -> IO ()
333 writeIORef (IORef var) v = stToIO (writeSTRef var v)
335 -- ---------------------------------------------------------------------------
336 -- Show instance for Handles
338 -- handle types are 'show'n when printing error msgs, so
339 -- we provide a more user-friendly Show instance for it
340 -- than the derived one.
342 instance Show HandleType where
345 ClosedHandle -> showString "closed"
346 SemiClosedHandle -> showString "semi-closed"
347 ReadHandle -> showString "readable"
348 WriteHandle -> showString "writable"
349 AppendHandle -> showString "writable (append)"
350 ReadWriteHandle -> showString "read-writable"
352 instance Show Handle where
353 showsPrec p (FileHandle h) = showHandle p h False
354 showsPrec p (DuplexHandle _ h) = showHandle p h True
356 showHandle p h duplex =
358 -- (Big) SIGH: unfolded defn of takeMVar to avoid
359 -- an (oh-so) unfortunate module loop with GHC.Conc.
360 hdl_ = unsafePerformIO (IO $ \ s# ->
361 case h of { MVar h# ->
362 case takeMVar# h# s# of { (# s2# , r #) ->
363 case putMVar# h# r s2# of { s3# ->
366 showType | duplex = showString "duplex (read-write)"
367 | otherwise = showsPrec p (haType hdl_)
370 showHdl (haType hdl_)
371 (showString "loc=" . showString (haFilePath hdl_) . showChar ',' .
372 showString "type=" . showType . showChar ',' .
373 showString "binary=" . showsPrec p (haIsBin hdl_) . showChar ',' .
374 showString "buffering=" . showBufMode (unsafePerformIO (readIORef (haBuffer hdl_))) (haBufferMode hdl_) . showString "}" )
377 showHdl :: HandleType -> ShowS -> ShowS
380 ClosedHandle -> showsPrec p ht . showString "}"
383 showBufMode :: Buffer -> BufferMode -> ShowS
384 showBufMode buf bmo =
386 NoBuffering -> showString "none"
387 LineBuffering -> showString "line"
388 BlockBuffering (Just n) -> showString "block " . showParen True (showsPrec p n)
389 BlockBuffering Nothing -> showString "block " . showParen True (showsPrec p def)
394 -- ------------------------------------------------------------------------
395 -- Exception datatype and operations
398 = IOException IOException -- IO exceptions
399 | ArithException ArithException -- Arithmetic exceptions
400 | ArrayException ArrayException -- Array-related exceptions
401 | ErrorCall String -- Calls to 'error'
402 | ExitException ExitCode -- Call to System.exitWith
403 | NoMethodError String -- A non-existent method was invoked
404 | PatternMatchFail String -- A pattern match / guard failure
405 | RecSelError String -- Selecting a non-existent field
406 | RecConError String -- Field missing in record construction
407 | RecUpdError String -- Record doesn't contain updated field
408 | AssertionFailed String -- Assertions
409 | DynException Dynamic -- Dynamic exceptions
410 | AsyncException AsyncException -- Externally generated errors
411 | BlockedOnDeadMVar -- Blocking on a dead MVar
412 | Deadlock -- no threads can run (raised in main thread)
430 = IndexOutOfBounds String -- out-of-range array access
431 | UndefinedElement String -- evaluating an undefined element
434 stackOverflow, heapOverflow :: Exception -- for the RTS
435 stackOverflow = AsyncException StackOverflow
436 heapOverflow = AsyncException HeapOverflow
438 instance Show ArithException where
439 showsPrec _ Overflow = showString "arithmetic overflow"
440 showsPrec _ Underflow = showString "arithmetic underflow"
441 showsPrec _ LossOfPrecision = showString "loss of precision"
442 showsPrec _ DivideByZero = showString "divide by zero"
443 showsPrec _ Denormal = showString "denormal"
445 instance Show AsyncException where
446 showsPrec _ StackOverflow = showString "stack overflow"
447 showsPrec _ HeapOverflow = showString "heap overflow"
448 showsPrec _ ThreadKilled = showString "thread killed"
450 instance Show ArrayException where
451 showsPrec _ (IndexOutOfBounds s)
452 = showString "array index out of range"
453 . (if not (null s) then showString ": " . showString s
455 showsPrec _ (UndefinedElement s)
456 = showString "undefined array element"
457 . (if not (null s) then showString ": " . showString s
460 instance Show Exception where
461 showsPrec _ (IOException err) = shows err
462 showsPrec _ (ArithException err) = shows err
463 showsPrec _ (ArrayException err) = shows err
464 showsPrec _ (ErrorCall err) = showString err
465 showsPrec _ (ExitException err) = showString "exit: " . shows err
466 showsPrec _ (NoMethodError err) = showString err
467 showsPrec _ (PatternMatchFail err) = showString err
468 showsPrec _ (RecSelError err) = showString err
469 showsPrec _ (RecConError err) = showString err
470 showsPrec _ (RecUpdError err) = showString err
471 showsPrec _ (AssertionFailed err) = showString err
472 showsPrec _ (DynException _err) = showString "unknown exception"
473 showsPrec _ (AsyncException e) = shows e
474 showsPrec _ (BlockedOnDeadMVar) = showString "thread blocked indefinitely"
475 showsPrec _ (NonTermination) = showString "<<loop>>"
476 showsPrec _ (Deadlock) = showString "<<deadlock>>"
478 instance Eq Exception where
479 IOException e1 == IOException e2 = e1 == e2
480 ArithException e1 == ArithException e2 = e1 == e2
481 ArrayException e1 == ArrayException e2 = e1 == e2
482 ErrorCall e1 == ErrorCall e2 = e1 == e2
483 ExitException e1 == ExitException e2 = e1 == e2
484 NoMethodError e1 == NoMethodError e2 = e1 == e2
485 PatternMatchFail e1 == PatternMatchFail e2 = e1 == e2
486 RecSelError e1 == RecSelError e2 = e1 == e2
487 RecConError e1 == RecConError e2 = e1 == e2
488 RecUpdError e1 == RecUpdError e2 = e1 == e2
489 AssertionFailed e1 == AssertionFailed e2 = e1 == e2
490 DynException _ == DynException _ = False -- incomparable
491 AsyncException e1 == AsyncException e2 = e1 == e2
492 BlockedOnDeadMVar == BlockedOnDeadMVar = True
493 NonTermination == NonTermination = True
494 Deadlock == Deadlock = True
496 -- -----------------------------------------------------------------------------
499 -- The `ExitCode' type defines the exit codes that a program
500 -- can return. `ExitSuccess' indicates successful termination;
501 -- and `ExitFailure code' indicates program failure
502 -- with value `code'. The exact interpretation of `code'
503 -- is operating-system dependent. In particular, some values of
504 -- `code' may be prohibited (e.g. 0 on a POSIX-compliant system).
506 -- We need it here because it is used in ExitException in the
507 -- Exception datatype (above).
509 data ExitCode = ExitSuccess | ExitFailure Int
510 deriving (Eq, Ord, Read, Show)
512 -- --------------------------------------------------------------------------
515 throw :: Exception -> a
516 throw exception = raise# exception
518 ioError :: Exception -> IO a
519 ioError err = IO $ \s -> throw err s
521 ioException :: IOException -> IO a
522 ioException err = IO $ \s -> throw (IOException err) s
524 -- ---------------------------------------------------------------------------
527 -- A value @IOError@ encode errors occurred in the @IO@ monad.
528 -- An @IOError@ records a more specific error type, a descriptive
529 -- string and maybe the handle that was used when the error was
532 type IOError = Exception
536 ioe_handle :: Maybe Handle, -- the handle used by the action flagging
538 ioe_type :: IOErrorType, -- what it was.
539 ioe_location :: String, -- location.
540 ioe_descr :: String, -- error type specific information.
541 ioe_filename :: Maybe FilePath -- filename the error is related to.
544 instance Eq IOException where
545 (IOError h1 e1 loc1 str1 fn1) == (IOError h2 e2 loc2 str2 fn2) =
546 e1==e2 && str1==str2 && h1==h2 && loc1==loc2 && fn1==fn2
559 | UnsatisfiedConstraints
566 | UnsupportedOperation
570 | DynIOError Dynamic -- cheap&cheerful extensible IO error type.
572 instance Eq IOErrorType where
575 DynIOError{} -> False -- from a strictness POV, compatible with a derived Eq inst?
576 _ -> getTag# x ==# getTag# y
578 instance Show IOErrorType where
582 AlreadyExists -> "already exists"
583 NoSuchThing -> "does not exist"
584 ResourceBusy -> "resource busy"
585 ResourceExhausted -> "resource exhausted"
587 IllegalOperation -> "illegal operation"
588 PermissionDenied -> "permission denied"
589 UserError -> "user error"
590 HardwareFault -> "hardware fault"
591 InappropriateType -> "inappropriate type"
592 Interrupted -> "interrupted"
593 InvalidArgument -> "invalid argument"
594 OtherError -> "failed"
595 ProtocolError -> "protocol error"
596 ResourceVanished -> "resource vanished"
597 SystemError -> "system error"
598 TimeExpired -> "timeout"
599 UnsatisfiedConstraints -> "unsatisified constraints" -- ultra-precise!
600 UnsupportedOperation -> "unsupported operation"
601 DynIOError{} -> "unknown IO error"
603 userError :: String -> IOError
604 userError str = IOException (IOError Nothing UserError "" str Nothing)
606 -- ---------------------------------------------------------------------------
609 instance Show IOException where
610 showsPrec p (IOError hdl iot loc s fn) =
614 _ -> showString "\nAction: " . showString loc) .
617 Just h -> showString "\nHandle: " . showsPrec p h) .
620 _ -> showString "\nReason: " . showString s) .
623 Just name -> showString "\nFile: " . showString name)