1 {-# OPTIONS_GHC -XNoImplicitPrelude -XRecordWildCards #-}
2 {-# OPTIONS_GHC -fno-warn-unused-matches #-}
3 -----------------------------------------------------------------------------
5 -- Module : GHC.IO.Handle
6 -- Copyright : (c) The University of Glasgow, 1994-2009
7 -- License : see libraries/base/LICENSE
9 -- Maintainer : libraries@haskell.org
10 -- Stability : provisional
11 -- Portability : non-portable
13 -- External API for GHC's Handle implementation
15 -----------------------------------------------------------------------------
17 module GHC.IO.Handle (
21 mkFileHandle, mkDuplexHandle,
23 hFileSize, hSetFileSize, hIsEOF, hLookAhead,
24 hSetBuffering, hSetBinaryMode, hSetEncoding, hGetEncoding,
25 hFlush, hFlushAll, hDuplicate, hDuplicateTo,
29 HandlePosition, HandlePosn(..), hGetPosn, hSetPosn,
30 SeekMode(..), hSeek, hTell,
32 hIsOpen, hIsClosed, hIsReadable, hIsWritable, hGetBuffering, hIsSeekable,
33 hSetEcho, hGetEcho, hIsTerminalDevice,
35 hSetNewlineMode, Newline(..), NewlineMode(..), nativeNewline,
36 noNewlineTranslation, universalNewlineMode, nativeNewlineMode,
40 hWaitForInput, hGetChar, hGetLine, hGetContents, hPutChar, hPutStr,
42 hGetBuf, hGetBufNonBlocking, hPutBuf, hPutBufNonBlocking
46 import GHC.IO.Exception
47 import GHC.IO.Encoding
49 import GHC.IO.BufferedIO ( BufferedIO )
50 import GHC.IO.Device as IODevice
51 import GHC.IO.Handle.Types
52 import GHC.IO.Handle.Internals
53 import GHC.IO.Handle.Text
54 import System.IO.Error
67 -- ---------------------------------------------------------------------------
70 -- | Computation 'hClose' @hdl@ makes handle @hdl@ closed. Before the
71 -- computation finishes, if @hdl@ is writable its buffer is flushed as
73 -- Performing 'hClose' on a handle that has already been closed has no effect;
74 -- doing so is not an error. All other operations on a closed handle will fail.
75 -- If 'hClose' fails for any reason, any further operations (apart from
76 -- 'hClose') on the handle will still fail as if @hdl@ had been successfully
79 hClose :: Handle -> IO ()
80 hClose h@(FileHandle _ m) = do
82 hClose_maybethrow mb_exc h
83 hClose h@(DuplexHandle _ r w) = do
84 mb_exc1 <- hClose' h w
85 mb_exc2 <- hClose' h r
88 Just e -> hClose_maybethrow mb_exc2 h
90 hClose_maybethrow :: Maybe SomeException -> Handle -> IO ()
91 hClose_maybethrow Nothing h = return ()
92 hClose_maybethrow (Just e) h = hClose_rethrow e h
94 hClose_rethrow :: SomeException -> Handle -> IO ()
96 case fromException e of
97 Just ioe -> ioError (augmentIOError ioe "hClose" h)
100 hClose' :: Handle -> MVar Handle__ -> IO (Maybe SomeException)
101 hClose' h m = withHandle' "hClose" h m $ hClose_help
103 -----------------------------------------------------------------------------
104 -- Detecting and changing the size of a file
106 -- | For a handle @hdl@ which attached to a physical file,
107 -- 'hFileSize' @hdl@ returns the size of that file in 8-bit bytes.
109 hFileSize :: Handle -> IO Integer
111 withHandle_ "hFileSize" handle $ \ handle_@Handle__{haDevice=dev} -> do
112 case haType handle_ of
113 ClosedHandle -> ioe_closedHandle
114 SemiClosedHandle -> ioe_closedHandle
115 _ -> do flushWriteBuffer handle_
116 r <- IODevice.getSize dev
119 else ioException (IOError Nothing InappropriateType "hFileSize"
120 "not a regular file" Nothing Nothing)
123 -- | 'hSetFileSize' @hdl@ @size@ truncates the physical file with handle @hdl@ to @size@ bytes.
125 hSetFileSize :: Handle -> Integer -> IO ()
126 hSetFileSize handle size =
127 withHandle_ "hSetFileSize" handle $ \ handle_@Handle__{haDevice=dev} -> do
128 case haType handle_ of
129 ClosedHandle -> ioe_closedHandle
130 SemiClosedHandle -> ioe_closedHandle
131 _ -> do flushWriteBuffer handle_
132 IODevice.setSize dev size
135 -- ---------------------------------------------------------------------------
136 -- Detecting the End of Input
138 -- | For a readable handle @hdl@, 'hIsEOF' @hdl@ returns
139 -- 'True' if no further input can be taken from @hdl@ or for a
140 -- physical file, if the current I\/O position is equal to the length of
141 -- the file. Otherwise, it returns 'False'.
143 -- NOTE: 'hIsEOF' may block, because it is the same as calling
144 -- 'hLookAhead' and checking for an EOF exception.
146 hIsEOF :: Handle -> IO Bool
149 (hLookAhead handle >> return False)
150 (\e -> if isEOFError e then return True else ioError e)
152 -- ---------------------------------------------------------------------------
155 -- | Computation 'hLookAhead' returns the next character from the handle
156 -- without removing it from the input buffer, blocking until a character
159 -- This operation may fail with:
161 -- * 'isEOFError' if the end of file has been reached.
163 hLookAhead :: Handle -> IO Char
165 wantReadableHandle_ "hLookAhead" handle hLookAhead_
167 -- ---------------------------------------------------------------------------
168 -- Buffering Operations
170 -- Three kinds of buffering are supported: line-buffering,
171 -- block-buffering or no-buffering. See GHC.IO.Handle for definition and
172 -- further explanation of what the type represent.
174 -- | Computation 'hSetBuffering' @hdl mode@ sets the mode of buffering for
175 -- handle @hdl@ on subsequent reads and writes.
177 -- If the buffer mode is changed from 'BlockBuffering' or
178 -- 'LineBuffering' to 'NoBuffering', then
180 -- * if @hdl@ is writable, the buffer is flushed as for 'hFlush';
182 -- * if @hdl@ is not writable, the contents of the buffer is discarded.
184 -- This operation may fail with:
186 -- * 'isPermissionError' if the handle has already been used for reading
187 -- or writing and the implementation does not allow the buffering mode
190 hSetBuffering :: Handle -> BufferMode -> IO ()
191 hSetBuffering handle mode =
192 withAllHandles__ "hSetBuffering" handle $ \ handle_@Handle__{..} -> do
194 ClosedHandle -> ioe_closedHandle
196 if mode == haBufferMode then return handle_ else do
199 - we flush the old buffer regardless of whether
200 the new buffer could fit the contents of the old buffer
202 - allow a handle's buffering to change even if IO has
203 occurred (ANSI C spec. does not allow this, nor did
204 the previous implementation of IO.hSetBuffering).
205 - a non-standard extension is to allow the buffering
206 of semi-closed handles to change [sof 6/98]
208 flushCharBuffer handle_
210 let state = initBufferState haType
211 reading = not (isWritableHandleType haType)
215 -- See [note Buffer Sizing], GHC.IO.Handle.Types
216 NoBuffering | reading -> newCharBuffer dEFAULT_CHAR_BUFFER_SIZE state
217 | otherwise -> newCharBuffer 1 state
218 LineBuffering -> newCharBuffer dEFAULT_CHAR_BUFFER_SIZE state
219 BlockBuffering Nothing -> newCharBuffer dEFAULT_CHAR_BUFFER_SIZE state
220 BlockBuffering (Just n) | n <= 0 -> ioe_bufsiz n
221 | otherwise -> newCharBuffer n state
223 writeIORef haCharBuffer new_buf
225 -- for input terminals we need to put the terminal into
226 -- cooked or raw mode depending on the type of buffering.
227 is_tty <- IODevice.isTerminal haDevice
228 when (is_tty && isReadableHandleType haType) $
230 #ifndef mingw32_HOST_OS
231 -- 'raw' mode under win32 is a bit too specialised (and troublesome
232 -- for most common uses), so simply disable its use here.
233 NoBuffering -> IODevice.setRaw haDevice True
235 NoBuffering -> return ()
237 _ -> IODevice.setRaw haDevice False
239 -- throw away spare buffers, they might be the wrong size
240 writeIORef haBuffers BufferListNil
242 return Handle__{ haBufferMode = mode,.. }
244 -- -----------------------------------------------------------------------------
247 -- | The action 'hSetEncoding' @hdl@ @encoding@ changes the text encoding
248 -- for the handle @hdl@ to @encoding@. The default encoding when a 'Handle' is
249 -- created is 'localeEncoding', namely the default encoding for the current
252 -- To create a 'Handle' with no encoding at all, use 'openBinaryFile'. To
253 -- stop further encoding or decoding on an existing 'Handle', use
256 -- 'hSetEncoding' may need to flush buffered data in order to change
259 hSetEncoding :: Handle -> TextEncoding -> IO ()
260 hSetEncoding hdl encoding = do
261 withHandle "hSetEncoding" hdl $ \h_@Handle__{..} -> do
263 openTextEncoding (Just encoding) haType $ \ mb_encoder mb_decoder -> do
264 bbuf <- readIORef haByteBuffer
265 ref <- newIORef (error "last_decode")
266 return (Handle__{ haLastDecode = ref,
267 haDecoder = mb_decoder,
268 haEncoder = mb_encoder,
269 haCodec = Just encoding, .. },
272 -- | Return the current 'TextEncoding' for the specified 'Handle', or
273 -- 'Nothing' if the 'Handle' is in binary mode.
275 -- Note that the 'TextEncoding' remembers nothing about the state of
276 -- the encoder/decoder in use on this 'Handle'. For example, if the
277 -- encoding in use is UTF-16, then using 'hGetEncoding' and
278 -- 'hSetEncoding' to save and restore the encoding may result in an
279 -- extra byte-order-mark being written to the file.
281 hGetEncoding :: Handle -> IO (Maybe TextEncoding)
283 withHandle_ "hGetEncoding" hdl $ \h_@Handle__{..} -> return haCodec
285 -- -----------------------------------------------------------------------------
288 -- | The action 'hFlush' @hdl@ causes any items buffered for output
289 -- in handle @hdl@ to be sent immediately to the operating system.
291 -- This operation may fail with:
293 -- * 'isFullError' if the device is full;
295 -- * 'isPermissionError' if a system resource limit would be exceeded.
296 -- It is unspecified whether the characters in the buffer are discarded
297 -- or retained under these circumstances.
299 hFlush :: Handle -> IO ()
300 hFlush handle = wantWritableHandle "hFlush" handle flushWriteBuffer
302 -- | The action 'hFlushAll' @hdl@ flushes all buffered data in @hdl@,
303 -- including any buffered read data. Buffered read data is flushed
304 -- by seeking the file position back to the point before the bufferred
305 -- data was read, and hence only works if @hdl@ is seekable (see
308 -- This operation may fail with:
310 -- * 'isFullError' if the device is full;
312 -- * 'isPermissionError' if a system resource limit would be exceeded.
313 -- It is unspecified whether the characters in the buffer are discarded
314 -- or retained under these circumstances;
316 -- * 'isIllegalOperation' if @hdl@ has buffered read data, and is not
319 hFlushAll :: Handle -> IO ()
320 hFlushAll handle = withHandle_ "hFlushAll" handle flushBuffer
322 -- -----------------------------------------------------------------------------
323 -- Repositioning Handles
325 data HandlePosn = HandlePosn Handle HandlePosition
327 instance Eq HandlePosn where
328 (HandlePosn h1 p1) == (HandlePosn h2 p2) = p1==p2 && h1==h2
330 instance Show HandlePosn where
331 showsPrec p (HandlePosn h pos) =
332 showsPrec p h . showString " at position " . shows pos
334 -- HandlePosition is the Haskell equivalent of POSIX' off_t.
335 -- We represent it as an Integer on the Haskell side, but
336 -- cheat slightly in that hGetPosn calls upon a C helper
337 -- that reports the position back via (merely) an Int.
338 type HandlePosition = Integer
340 -- | Computation 'hGetPosn' @hdl@ returns the current I\/O position of
341 -- @hdl@ as a value of the abstract type 'HandlePosn'.
343 hGetPosn :: Handle -> IO HandlePosn
346 return (HandlePosn handle posn)
348 -- | If a call to 'hGetPosn' @hdl@ returns a position @p@,
349 -- then computation 'hSetPosn' @p@ sets the position of @hdl@
350 -- to the position it held at the time of the call to 'hGetPosn'.
352 -- This operation may fail with:
354 -- * 'isPermissionError' if a system resource limit would be exceeded.
356 hSetPosn :: HandlePosn -> IO ()
357 hSetPosn (HandlePosn h i) = hSeek h AbsoluteSeek i
359 -- ---------------------------------------------------------------------------
363 - when seeking using `SeekFromEnd', positive offsets (>=0) means
364 seeking at or past EOF.
366 - we possibly deviate from the report on the issue of seeking within
367 the buffer and whether to flush it or not. The report isn't exactly
371 -- | Computation 'hSeek' @hdl mode i@ sets the position of handle
372 -- @hdl@ depending on @mode@.
373 -- The offset @i@ is given in terms of 8-bit bytes.
375 -- If @hdl@ is block- or line-buffered, then seeking to a position which is not
376 -- in the current buffer will first cause any items in the output buffer to be
377 -- written to the device, and then cause the input buffer to be discarded.
378 -- Some handles may not be seekable (see 'hIsSeekable'), or only support a
379 -- subset of the possible positioning operations (for instance, it may only
380 -- be possible to seek to the end of a tape, or to a positive offset from
381 -- the beginning or current position).
382 -- It is not possible to set a negative I\/O position, or for
383 -- a physical file, an I\/O position beyond the current end-of-file.
385 -- This operation may fail with:
387 -- * 'isPermissionError' if a system resource limit would be exceeded.
389 hSeek :: Handle -> SeekMode -> Integer -> IO ()
390 hSeek handle mode offset =
391 wantSeekableHandle "hSeek" handle $ \ handle_@Handle__{..} -> do
392 debugIO ("hSeek " ++ show (mode,offset))
393 buf <- readIORef haCharBuffer
396 then do flushWriteBuffer handle_
397 IODevice.seek haDevice mode offset
400 let r = bufL buf; w = bufR buf
401 if mode == RelativeSeek && isNothing haDecoder &&
402 offset >= 0 && offset < fromIntegral (w - r)
403 then writeIORef haCharBuffer buf{ bufL = r + fromIntegral offset }
406 flushCharReadBuffer handle_
407 flushByteReadBuffer handle_
408 IODevice.seek haDevice mode offset
411 hTell :: Handle -> IO Integer
413 wantSeekableHandle "hGetPosn" handle $ \ handle_@Handle__{..} -> do
415 posn <- IODevice.tell haDevice
417 cbuf <- readIORef haCharBuffer
418 bbuf <- readIORef haByteBuffer
421 | isWriteBuffer cbuf = posn + fromIntegral (bufR cbuf)
422 | otherwise = posn - fromIntegral (bufR cbuf - bufL cbuf)
423 - fromIntegral (bufR bbuf - bufL bbuf)
425 debugIO ("\nhGetPosn: (posn, real_posn) = " ++ show (posn, real_posn))
426 debugIO (" cbuf: " ++ summaryBuffer cbuf ++
427 " bbuf: " ++ summaryBuffer bbuf)
431 -- -----------------------------------------------------------------------------
434 -- A number of operations return information about the properties of a
435 -- handle. Each of these operations returns `True' if the handle has
436 -- the specified property, and `False' otherwise.
438 hIsOpen :: Handle -> IO Bool
440 withHandle_ "hIsOpen" handle $ \ handle_ -> do
441 case haType handle_ of
442 ClosedHandle -> return False
443 SemiClosedHandle -> return False
446 hIsClosed :: Handle -> IO Bool
448 withHandle_ "hIsClosed" handle $ \ handle_ -> do
449 case haType handle_ of
450 ClosedHandle -> return True
453 {- not defined, nor exported, but mentioned
454 here for documentation purposes:
456 hSemiClosed :: Handle -> IO Bool
460 return (not (ho || hc))
463 hIsReadable :: Handle -> IO Bool
464 hIsReadable (DuplexHandle _ _ _) = return True
466 withHandle_ "hIsReadable" handle $ \ handle_ -> do
467 case haType handle_ of
468 ClosedHandle -> ioe_closedHandle
469 SemiClosedHandle -> ioe_closedHandle
470 htype -> return (isReadableHandleType htype)
472 hIsWritable :: Handle -> IO Bool
473 hIsWritable (DuplexHandle _ _ _) = return True
475 withHandle_ "hIsWritable" handle $ \ handle_ -> do
476 case haType handle_ of
477 ClosedHandle -> ioe_closedHandle
478 SemiClosedHandle -> ioe_closedHandle
479 htype -> return (isWritableHandleType htype)
481 -- | Computation 'hGetBuffering' @hdl@ returns the current buffering mode
484 hGetBuffering :: Handle -> IO BufferMode
485 hGetBuffering handle =
486 withHandle_ "hGetBuffering" handle $ \ handle_ -> do
487 case haType handle_ of
488 ClosedHandle -> ioe_closedHandle
490 -- We're being non-standard here, and allow the buffering
491 -- of a semi-closed handle to be queried. -- sof 6/98
492 return (haBufferMode handle_) -- could be stricter..
494 hIsSeekable :: Handle -> IO Bool
496 withHandle_ "hIsSeekable" handle $ \ handle_@Handle__{..} -> do
498 ClosedHandle -> ioe_closedHandle
499 SemiClosedHandle -> ioe_closedHandle
500 AppendHandle -> return False
501 _ -> IODevice.isSeekable haDevice
503 -- -----------------------------------------------------------------------------
504 -- Changing echo status (Non-standard GHC extensions)
506 -- | Set the echoing status of a handle connected to a terminal.
508 hSetEcho :: Handle -> Bool -> IO ()
509 hSetEcho handle on = do
510 isT <- hIsTerminalDevice handle
514 withHandle_ "hSetEcho" handle $ \ Handle__{..} -> do
516 ClosedHandle -> ioe_closedHandle
517 _ -> IODevice.setEcho haDevice on
519 -- | Get the echoing status of a handle connected to a terminal.
521 hGetEcho :: Handle -> IO Bool
523 isT <- hIsTerminalDevice handle
527 withHandle_ "hGetEcho" handle $ \ Handle__{..} -> do
529 ClosedHandle -> ioe_closedHandle
530 _ -> IODevice.getEcho haDevice
532 -- | Is the handle connected to a terminal?
534 hIsTerminalDevice :: Handle -> IO Bool
535 hIsTerminalDevice handle = do
536 withHandle_ "hIsTerminalDevice" handle $ \ Handle__{..} -> do
538 ClosedHandle -> ioe_closedHandle
539 _ -> IODevice.isTerminal haDevice
541 -- -----------------------------------------------------------------------------
544 -- | Select binary mode ('True') or text mode ('False') on a open handle.
545 -- (See also 'openBinaryFile'.)
547 -- This has the same effect as calling 'hSetEncoding' with 'latin1', together
548 -- with 'hSetNewlineMode' with 'noNewlineTranslation'.
550 hSetBinaryMode :: Handle -> Bool -> IO ()
551 hSetBinaryMode handle bin =
552 withAllHandles__ "hSetBinaryMode" handle $ \ h_@Handle__{..} ->
556 let mb_te | bin = Nothing
557 | otherwise = Just localeEncoding
559 openTextEncoding mb_te haType $ \ mb_encoder mb_decoder -> do
561 -- should match the default newline mode, whatever that is
562 let nl | bin = noNewlineTranslation
563 | otherwise = nativeNewlineMode
565 bbuf <- readIORef haByteBuffer
566 ref <- newIORef (error "codec_state", bbuf)
568 return Handle__{ haLastDecode = ref,
569 haEncoder = mb_encoder,
570 haDecoder = mb_decoder,
572 haInputNL = inputNL nl,
573 haOutputNL = outputNL nl, .. }
575 -- -----------------------------------------------------------------------------
578 -- | Set the 'NewlineMode' on the specified 'Handle'. All buffered
579 -- data is flushed first.
580 hSetNewlineMode :: Handle -> NewlineMode -> IO ()
581 hSetNewlineMode handle NewlineMode{ inputNL=i, outputNL=o } =
582 withAllHandles__ "hSetNewlineMode" handle $ \h_@Handle__{..} ->
585 return h_{ haInputNL=i, haOutputNL=o }
587 -- -----------------------------------------------------------------------------
588 -- Duplicating a Handle
590 -- | Returns a duplicate of the original handle, with its own buffer.
591 -- The two Handles will share a file pointer, however. The original
592 -- handle's buffer is flushed, including discarding any input data,
593 -- before the handle is duplicated.
595 hDuplicate :: Handle -> IO Handle
596 hDuplicate h@(FileHandle path m) = do
597 withHandle_' "hDuplicate" h m $ \h_ ->
598 dupHandle path h Nothing h_ (Just handleFinalizer)
599 hDuplicate h@(DuplexHandle path r w) = do
600 write_side@(FileHandle _ write_m) <-
601 withHandle_' "hDuplicate" h w $ \h_ ->
602 dupHandle path h Nothing h_ (Just handleFinalizer)
603 read_side@(FileHandle _ read_m) <-
604 withHandle_' "hDuplicate" h r $ \h_ ->
605 dupHandle path h (Just write_m) h_ Nothing
606 return (DuplexHandle path read_m write_m)
608 dupHandle :: FilePath
610 -> Maybe (MVar Handle__)
612 -> Maybe HandleFinalizer
614 dupHandle filepath h other_side h_@Handle__{..} mb_finalizer = do
615 -- flush the buffer first, so we don't have to copy its contents
619 new_dev <- IODevice.dup haDevice
620 dupHandle_ new_dev filepath other_side h_ mb_finalizer
622 withHandle_' "dupHandle" h r $ \Handle__{haDevice=dev} -> do
623 dupHandle_ dev filepath other_side h_ mb_finalizer
625 dupHandle_ :: (IODevice dev, BufferedIO dev, Typeable dev) => dev
627 -> Maybe (MVar Handle__)
629 -> Maybe HandleFinalizer
631 dupHandle_ new_dev filepath other_side h_@Handle__{..} mb_finalizer = do
633 let mb_codec = if isJust haEncoder then Just localeEncoding else Nothing
634 mkHandle new_dev filepath haType True{-buffered-} mb_codec
635 NewlineMode { inputNL = haInputNL, outputNL = haOutputNL }
636 mb_finalizer other_side
638 -- -----------------------------------------------------------------------------
639 -- Replacing a Handle
642 Makes the second handle a duplicate of the first handle. The second
643 handle will be closed first, if it is not already.
645 This can be used to retarget the standard Handles, for example:
647 > do h <- openFile "mystdout" WriteMode
648 > hDuplicateTo h stdout
651 hDuplicateTo :: Handle -> Handle -> IO ()
652 hDuplicateTo h1@(FileHandle path m1) h2@(FileHandle _ m2) = do
653 withHandle__' "hDuplicateTo" h2 m2 $ \h2_ -> do
655 withHandle_' "hDuplicateTo" h1 m1 $ \h1_ -> do
656 dupHandleTo path h1 Nothing h2_ h1_ (Just handleFinalizer)
657 hDuplicateTo h1@(DuplexHandle path r1 w1) h2@(DuplexHandle _ r2 w2) = do
658 withHandle__' "hDuplicateTo" h2 w2 $ \w2_ -> do
660 withHandle_' "hDuplicateTo" h1 w1 $ \w1_ -> do
661 dupHandleTo path h1 Nothing w2_ w1_ (Just handleFinalizer)
662 withHandle__' "hDuplicateTo" h2 r2 $ \r2_ -> do
664 withHandle_' "hDuplicateTo" h1 r1 $ \r1_ -> do
665 dupHandleTo path h1 (Just w1) r2_ r1_ Nothing
667 ioe_dupHandlesNotCompatible h1
670 ioe_dupHandlesNotCompatible :: Handle -> IO a
671 ioe_dupHandlesNotCompatible h =
672 ioException (IOError (Just h) IllegalOperation "hDuplicateTo"
673 "handles are incompatible" Nothing Nothing)
675 dupHandleTo :: FilePath
677 -> Maybe (MVar Handle__)
680 -> Maybe HandleFinalizer
682 dupHandleTo filepath h other_side
683 hto_@Handle__{haDevice=devTo,..}
684 h_@Handle__{haDevice=dev} mb_finalizer = do
687 Nothing -> ioe_dupHandlesNotCompatible h
689 _ <- IODevice.dup2 dev dev'
690 FileHandle _ m <- dupHandle_ dev' filepath other_side h_ mb_finalizer
693 -- ---------------------------------------------------------------------------
696 -- | 'hShow' is in the 'IO' monad, and gives more comprehensive output
697 -- than the (pure) instance of 'Show' for 'Handle'.
699 hShow :: Handle -> IO String
700 hShow h@(FileHandle path _) = showHandle' path False h
701 hShow h@(DuplexHandle path _ _) = showHandle' path True h
703 showHandle' :: String -> Bool -> Handle -> IO String
704 showHandle' filepath is_duplex h =
705 withHandle_ "showHandle" h $ \hdl_ ->
707 showType | is_duplex = showString "duplex (read-write)"
708 | otherwise = shows (haType hdl_)
712 showHdl (haType hdl_)
713 (showString "loc=" . showString filepath . showChar ',' .
714 showString "type=" . showType . showChar ',' .
715 showString "buffering=" . showBufMode (unsafePerformIO (readIORef (haCharBuffer hdl_))) (haBufferMode hdl_) . showString "}" )
719 showHdl :: HandleType -> ShowS -> ShowS
722 ClosedHandle -> shows ht . showString "}"
725 showBufMode :: Buffer e -> BufferMode -> ShowS
726 showBufMode buf bmo =
728 NoBuffering -> showString "none"
729 LineBuffering -> showString "line"
730 BlockBuffering (Just n) -> showString "block " . showParen True (shows n)
731 BlockBuffering Nothing -> showString "block " . showParen True (shows def)