1 {-# OPTIONS_GHC -fno-warn-unused-matches #-}
2 {-# LANGUAGE NoImplicitPrelude, RecordWildCards #-}
4 -----------------------------------------------------------------------------
6 -- Module : GHC.IO.Handle
7 -- Copyright : (c) The University of Glasgow, 1994-2009
8 -- License : see libraries/base/LICENSE
10 -- Maintainer : libraries@haskell.org
11 -- Stability : provisional
12 -- Portability : non-portable
14 -- External API for GHC's Handle implementation
16 -----------------------------------------------------------------------------
18 module GHC.IO.Handle (
22 mkFileHandle, mkDuplexHandle,
24 hFileSize, hSetFileSize, hIsEOF, hLookAhead,
25 hSetBuffering, hSetBinaryMode, hSetEncoding, hGetEncoding,
26 hFlush, hFlushAll, hDuplicate, hDuplicateTo,
30 HandlePosition, HandlePosn(..), hGetPosn, hSetPosn,
31 SeekMode(..), hSeek, hTell,
33 hIsOpen, hIsClosed, hIsReadable, hIsWritable, hGetBuffering, hIsSeekable,
34 hSetEcho, hGetEcho, hIsTerminalDevice,
36 hSetNewlineMode, Newline(..), NewlineMode(..), nativeNewline,
37 noNewlineTranslation, universalNewlineMode, nativeNewlineMode,
41 hWaitForInput, hGetChar, hGetLine, hGetContents, hPutChar, hPutStr,
43 hGetBuf, hGetBufNonBlocking, hPutBuf, hPutBufNonBlocking
47 import GHC.IO.Exception
48 import GHC.IO.Encoding
50 import GHC.IO.BufferedIO ( BufferedIO )
51 import GHC.IO.Device as IODevice
52 import GHC.IO.Handle.Types
53 import GHC.IO.Handle.Internals
54 import GHC.IO.Handle.Text
55 import qualified GHC.IO.BufferedIO as Buffered
68 -- ---------------------------------------------------------------------------
71 -- | Computation 'hClose' @hdl@ makes handle @hdl@ closed. Before the
72 -- computation finishes, if @hdl@ is writable its buffer is flushed as
74 -- Performing 'hClose' on a handle that has already been closed has no effect;
75 -- doing so is not an error. All other operations on a closed handle will fail.
76 -- If 'hClose' fails for any reason, any further operations (apart from
77 -- 'hClose') on the handle will still fail as if @hdl@ had been successfully
80 hClose :: Handle -> IO ()
81 hClose h@(FileHandle _ m) = do
83 hClose_maybethrow mb_exc h
84 hClose h@(DuplexHandle _ r w) = do
85 excs <- mapM (hClose' h) [r,w]
86 hClose_maybethrow (listToMaybe (catMaybes excs)) h
88 hClose_maybethrow :: Maybe SomeException -> Handle -> IO ()
89 hClose_maybethrow Nothing h = return ()
90 hClose_maybethrow (Just e) h = hClose_rethrow e h
92 hClose_rethrow :: SomeException -> Handle -> IO ()
94 case fromException e of
95 Just ioe -> ioError (augmentIOError ioe "hClose" h)
98 hClose' :: Handle -> MVar Handle__ -> IO (Maybe SomeException)
99 hClose' h m = withHandle' "hClose" h m $ hClose_help
101 -----------------------------------------------------------------------------
102 -- Detecting and changing the size of a file
104 -- | For a handle @hdl@ which attached to a physical file,
105 -- 'hFileSize' @hdl@ returns the size of that file in 8-bit bytes.
107 hFileSize :: Handle -> IO Integer
109 withHandle_ "hFileSize" handle $ \ handle_@Handle__{haDevice=dev} -> do
110 case haType handle_ of
111 ClosedHandle -> ioe_closedHandle
112 SemiClosedHandle -> ioe_closedHandle
113 _ -> do flushWriteBuffer handle_
114 r <- IODevice.getSize dev
117 else ioException (IOError Nothing InappropriateType "hFileSize"
118 "not a regular file" Nothing Nothing)
121 -- | 'hSetFileSize' @hdl@ @size@ truncates the physical file with handle @hdl@ to @size@ bytes.
123 hSetFileSize :: Handle -> Integer -> IO ()
124 hSetFileSize handle size =
125 withHandle_ "hSetFileSize" handle $ \ handle_@Handle__{haDevice=dev} -> do
126 case haType handle_ of
127 ClosedHandle -> ioe_closedHandle
128 SemiClosedHandle -> ioe_closedHandle
129 _ -> do flushWriteBuffer handle_
130 IODevice.setSize dev size
133 -- ---------------------------------------------------------------------------
134 -- Detecting the End of Input
136 -- | For a readable handle @hdl@, 'hIsEOF' @hdl@ returns
137 -- 'True' if no further input can be taken from @hdl@ or for a
138 -- physical file, if the current I\/O position is equal to the length of
139 -- the file. Otherwise, it returns 'False'.
141 -- NOTE: 'hIsEOF' may block, because it has to attempt to read from
142 -- the stream to determine whether there is any more data to be read.
144 hIsEOF :: Handle -> IO Bool
145 hIsEOF handle = wantReadableHandle_ "hIsEOF" handle $ \Handle__{..} -> do
147 cbuf <- readIORef haCharBuffer
148 if not (isEmptyBuffer cbuf) then return False else do
150 bbuf <- readIORef haByteBuffer
151 if not (isEmptyBuffer bbuf) then return False else do
153 -- NB. do no decoding, just fill the byte buffer; see #3808
154 (r,bbuf') <- Buffered.fillReadBuffer haDevice bbuf
157 else do writeIORef haByteBuffer bbuf'
160 -- ---------------------------------------------------------------------------
163 -- | Computation 'hLookAhead' returns the next character from the handle
164 -- without removing it from the input buffer, blocking until a character
167 -- This operation may fail with:
169 -- * 'isEOFError' if the end of file has been reached.
171 hLookAhead :: Handle -> IO Char
173 wantReadableHandle_ "hLookAhead" handle hLookAhead_
175 -- ---------------------------------------------------------------------------
176 -- Buffering Operations
178 -- Three kinds of buffering are supported: line-buffering,
179 -- block-buffering or no-buffering. See GHC.IO.Handle for definition and
180 -- further explanation of what the type represent.
182 -- | Computation 'hSetBuffering' @hdl mode@ sets the mode of buffering for
183 -- handle @hdl@ on subsequent reads and writes.
185 -- If the buffer mode is changed from 'BlockBuffering' or
186 -- 'LineBuffering' to 'NoBuffering', then
188 -- * if @hdl@ is writable, the buffer is flushed as for 'hFlush';
190 -- * if @hdl@ is not writable, the contents of the buffer is discarded.
192 -- This operation may fail with:
194 -- * 'isPermissionError' if the handle has already been used for reading
195 -- or writing and the implementation does not allow the buffering mode
198 hSetBuffering :: Handle -> BufferMode -> IO ()
199 hSetBuffering handle mode =
200 withAllHandles__ "hSetBuffering" handle $ \ handle_@Handle__{..} -> do
202 ClosedHandle -> ioe_closedHandle
204 if mode == haBufferMode then return handle_ else do
206 -- See [note Buffer Sizing] in GHC.IO.Handle.Types
210 BlockBuffering (Just n) | n <= 0 -> ioe_bufsiz n
213 -- for input terminals we need to put the terminal into
214 -- cooked or raw mode depending on the type of buffering.
215 is_tty <- IODevice.isTerminal haDevice
216 when (is_tty && isReadableHandleType haType) $
218 #ifndef mingw32_HOST_OS
219 -- 'raw' mode under win32 is a bit too specialised (and troublesome
220 -- for most common uses), so simply disable its use here.
221 NoBuffering -> IODevice.setRaw haDevice True
223 NoBuffering -> return ()
225 _ -> IODevice.setRaw haDevice False
227 -- throw away spare buffers, they might be the wrong size
228 writeIORef haBuffers BufferListNil
230 return Handle__{ haBufferMode = mode,.. }
232 -- -----------------------------------------------------------------------------
235 -- | The action 'hSetEncoding' @hdl@ @encoding@ changes the text encoding
236 -- for the handle @hdl@ to @encoding@. The default encoding when a 'Handle' is
237 -- created is 'localeEncoding', namely the default encoding for the current
240 -- To create a 'Handle' with no encoding at all, use 'openBinaryFile'. To
241 -- stop further encoding or decoding on an existing 'Handle', use
244 -- 'hSetEncoding' may need to flush buffered data in order to change
247 hSetEncoding :: Handle -> TextEncoding -> IO ()
248 hSetEncoding hdl encoding = do
249 withAllHandles__ "hSetEncoding" hdl $ \h_@Handle__{..} -> do
252 openTextEncoding (Just encoding) haType $ \ mb_encoder mb_decoder -> do
253 bbuf <- readIORef haByteBuffer
254 ref <- newIORef (error "last_decode")
255 return (Handle__{ haLastDecode = ref,
256 haDecoder = mb_decoder,
257 haEncoder = mb_encoder,
258 haCodec = Just encoding, .. })
260 -- | Return the current 'TextEncoding' for the specified 'Handle', or
261 -- 'Nothing' if the 'Handle' is in binary mode.
263 -- Note that the 'TextEncoding' remembers nothing about the state of
264 -- the encoder/decoder in use on this 'Handle'. For example, if the
265 -- encoding in use is UTF-16, then using 'hGetEncoding' and
266 -- 'hSetEncoding' to save and restore the encoding may result in an
267 -- extra byte-order-mark being written to the file.
269 hGetEncoding :: Handle -> IO (Maybe TextEncoding)
271 withHandle_ "hGetEncoding" hdl $ \h_@Handle__{..} -> return haCodec
273 -- -----------------------------------------------------------------------------
276 -- | The action 'hFlush' @hdl@ causes any items buffered for output
277 -- in handle @hdl@ to be sent immediately to the operating system.
279 -- This operation may fail with:
281 -- * 'isFullError' if the device is full;
283 -- * 'isPermissionError' if a system resource limit would be exceeded.
284 -- It is unspecified whether the characters in the buffer are discarded
285 -- or retained under these circumstances.
287 hFlush :: Handle -> IO ()
288 hFlush handle = wantWritableHandle "hFlush" handle flushWriteBuffer
290 -- | The action 'hFlushAll' @hdl@ flushes all buffered data in @hdl@,
291 -- including any buffered read data. Buffered read data is flushed
292 -- by seeking the file position back to the point before the bufferred
293 -- data was read, and hence only works if @hdl@ is seekable (see
296 -- This operation may fail with:
298 -- * 'isFullError' if the device is full;
300 -- * 'isPermissionError' if a system resource limit would be exceeded.
301 -- It is unspecified whether the characters in the buffer are discarded
302 -- or retained under these circumstances;
304 -- * 'isIllegalOperation' if @hdl@ has buffered read data, and is not
307 hFlushAll :: Handle -> IO ()
308 hFlushAll handle = withHandle_ "hFlushAll" handle flushBuffer
310 -- -----------------------------------------------------------------------------
311 -- Repositioning Handles
313 data HandlePosn = HandlePosn Handle HandlePosition
315 instance Eq HandlePosn where
316 (HandlePosn h1 p1) == (HandlePosn h2 p2) = p1==p2 && h1==h2
318 instance Show HandlePosn where
319 showsPrec p (HandlePosn h pos) =
320 showsPrec p h . showString " at position " . shows pos
322 -- HandlePosition is the Haskell equivalent of POSIX' off_t.
323 -- We represent it as an Integer on the Haskell side, but
324 -- cheat slightly in that hGetPosn calls upon a C helper
325 -- that reports the position back via (merely) an Int.
326 type HandlePosition = Integer
328 -- | Computation 'hGetPosn' @hdl@ returns the current I\/O position of
329 -- @hdl@ as a value of the abstract type 'HandlePosn'.
331 hGetPosn :: Handle -> IO HandlePosn
334 return (HandlePosn handle posn)
336 -- | If a call to 'hGetPosn' @hdl@ returns a position @p@,
337 -- then computation 'hSetPosn' @p@ sets the position of @hdl@
338 -- to the position it held at the time of the call to 'hGetPosn'.
340 -- This operation may fail with:
342 -- * 'isPermissionError' if a system resource limit would be exceeded.
344 hSetPosn :: HandlePosn -> IO ()
345 hSetPosn (HandlePosn h i) = hSeek h AbsoluteSeek i
347 -- ---------------------------------------------------------------------------
351 - when seeking using `SeekFromEnd', positive offsets (>=0) means
352 seeking at or past EOF.
354 - we possibly deviate from the report on the issue of seeking within
355 the buffer and whether to flush it or not. The report isn't exactly
359 -- | Computation 'hSeek' @hdl mode i@ sets the position of handle
360 -- @hdl@ depending on @mode@.
361 -- The offset @i@ is given in terms of 8-bit bytes.
363 -- If @hdl@ is block- or line-buffered, then seeking to a position which is not
364 -- in the current buffer will first cause any items in the output buffer to be
365 -- written to the device, and then cause the input buffer to be discarded.
366 -- Some handles may not be seekable (see 'hIsSeekable'), or only support a
367 -- subset of the possible positioning operations (for instance, it may only
368 -- be possible to seek to the end of a tape, or to a positive offset from
369 -- the beginning or current position).
370 -- It is not possible to set a negative I\/O position, or for
371 -- a physical file, an I\/O position beyond the current end-of-file.
373 -- This operation may fail with:
375 -- * 'isIllegalOperationError' if the Handle is not seekable, or does
376 -- not support the requested seek mode.
378 -- * 'isPermissionError' if a system resource limit would be exceeded.
380 hSeek :: Handle -> SeekMode -> Integer -> IO ()
381 hSeek handle mode offset =
382 wantSeekableHandle "hSeek" handle $ \ handle_@Handle__{..} -> do
383 debugIO ("hSeek " ++ show (mode,offset))
384 buf <- readIORef haCharBuffer
387 then do flushWriteBuffer handle_
388 IODevice.seek haDevice mode offset
391 let r = bufL buf; w = bufR buf
392 if mode == RelativeSeek && isNothing haDecoder &&
393 offset >= 0 && offset < fromIntegral (w - r)
394 then writeIORef haCharBuffer buf{ bufL = r + fromIntegral offset }
397 flushCharReadBuffer handle_
398 flushByteReadBuffer handle_
399 IODevice.seek haDevice mode offset
402 -- | Computation 'hTell' @hdl@ returns the current position of the
403 -- handle @hdl@, as the number of bytes from the beginning of
404 -- the file. The value returned may be subsequently passed to
405 -- 'hSeek' to reposition the handle to the current position.
407 -- This operation may fail with:
409 -- * 'isIllegalOperationError' if the Handle is not seekable.
411 hTell :: Handle -> IO Integer
413 wantSeekableHandle "hGetPosn" handle $ \ handle_@Handle__{..} -> do
415 posn <- IODevice.tell haDevice
417 -- we can't tell the real byte offset if there are buffered
418 -- Chars, so must flush first:
419 flushCharBuffer handle_
421 bbuf <- readIORef haByteBuffer
424 | isWriteBuffer bbuf = posn + fromIntegral (bufferElems bbuf)
425 | otherwise = posn - fromIntegral (bufferElems bbuf)
427 cbuf <- readIORef haCharBuffer
428 debugIO ("\nhGetPosn: (posn, real_posn) = " ++ show (posn, real_posn))
429 debugIO (" cbuf: " ++ summaryBuffer cbuf ++
430 " bbuf: " ++ summaryBuffer bbuf)
434 -- -----------------------------------------------------------------------------
437 -- A number of operations return information about the properties of a
438 -- handle. Each of these operations returns `True' if the handle has
439 -- the specified property, and `False' otherwise.
441 hIsOpen :: Handle -> IO Bool
443 withHandle_ "hIsOpen" handle $ \ handle_ -> do
444 case haType handle_ of
445 ClosedHandle -> return False
446 SemiClosedHandle -> return False
449 hIsClosed :: Handle -> IO Bool
451 withHandle_ "hIsClosed" handle $ \ handle_ -> do
452 case haType handle_ of
453 ClosedHandle -> return True
456 {- not defined, nor exported, but mentioned
457 here for documentation purposes:
459 hSemiClosed :: Handle -> IO Bool
463 return (not (ho || hc))
466 hIsReadable :: Handle -> IO Bool
467 hIsReadable (DuplexHandle _ _ _) = return True
469 withHandle_ "hIsReadable" handle $ \ handle_ -> do
470 case haType handle_ of
471 ClosedHandle -> ioe_closedHandle
472 SemiClosedHandle -> ioe_closedHandle
473 htype -> return (isReadableHandleType htype)
475 hIsWritable :: Handle -> IO Bool
476 hIsWritable (DuplexHandle _ _ _) = return True
478 withHandle_ "hIsWritable" handle $ \ handle_ -> do
479 case haType handle_ of
480 ClosedHandle -> ioe_closedHandle
481 SemiClosedHandle -> ioe_closedHandle
482 htype -> return (isWritableHandleType htype)
484 -- | Computation 'hGetBuffering' @hdl@ returns the current buffering mode
487 hGetBuffering :: Handle -> IO BufferMode
488 hGetBuffering handle =
489 withHandle_ "hGetBuffering" handle $ \ handle_ -> do
490 case haType handle_ of
491 ClosedHandle -> ioe_closedHandle
493 -- We're being non-standard here, and allow the buffering
494 -- of a semi-closed handle to be queried. -- sof 6/98
495 return (haBufferMode handle_) -- could be stricter..
497 hIsSeekable :: Handle -> IO Bool
499 withHandle_ "hIsSeekable" handle $ \ handle_@Handle__{..} -> do
501 ClosedHandle -> ioe_closedHandle
502 SemiClosedHandle -> ioe_closedHandle
503 AppendHandle -> return False
504 _ -> IODevice.isSeekable haDevice
506 -- -----------------------------------------------------------------------------
507 -- Changing echo status (Non-standard GHC extensions)
509 -- | Set the echoing status of a handle connected to a terminal.
511 hSetEcho :: Handle -> Bool -> IO ()
512 hSetEcho handle on = do
513 isT <- hIsTerminalDevice handle
517 withHandle_ "hSetEcho" handle $ \ Handle__{..} -> do
519 ClosedHandle -> ioe_closedHandle
520 _ -> IODevice.setEcho haDevice on
522 -- | Get the echoing status of a handle connected to a terminal.
524 hGetEcho :: Handle -> IO Bool
526 isT <- hIsTerminalDevice handle
530 withHandle_ "hGetEcho" handle $ \ Handle__{..} -> do
532 ClosedHandle -> ioe_closedHandle
533 _ -> IODevice.getEcho haDevice
535 -- | Is the handle connected to a terminal?
537 hIsTerminalDevice :: Handle -> IO Bool
538 hIsTerminalDevice handle = do
539 withHandle_ "hIsTerminalDevice" handle $ \ Handle__{..} -> do
541 ClosedHandle -> ioe_closedHandle
542 _ -> IODevice.isTerminal haDevice
544 -- -----------------------------------------------------------------------------
547 -- | Select binary mode ('True') or text mode ('False') on a open handle.
548 -- (See also 'openBinaryFile'.)
550 -- This has the same effect as calling 'hSetEncoding' with 'latin1', together
551 -- with 'hSetNewlineMode' with 'noNewlineTranslation'.
553 hSetBinaryMode :: Handle -> Bool -> IO ()
554 hSetBinaryMode handle bin =
555 withAllHandles__ "hSetBinaryMode" handle $ \ h_@Handle__{..} ->
560 let mb_te | bin = Nothing
561 | otherwise = Just localeEncoding
563 openTextEncoding mb_te haType $ \ mb_encoder mb_decoder -> do
565 -- should match the default newline mode, whatever that is
566 let nl | bin = noNewlineTranslation
567 | otherwise = nativeNewlineMode
569 bbuf <- readIORef haByteBuffer
570 ref <- newIORef (error "codec_state", bbuf)
572 return Handle__{ haLastDecode = ref,
573 haEncoder = mb_encoder,
574 haDecoder = mb_decoder,
576 haInputNL = inputNL nl,
577 haOutputNL = outputNL nl, .. }
579 -- -----------------------------------------------------------------------------
582 -- | Set the 'NewlineMode' on the specified 'Handle'. All buffered
583 -- data is flushed first.
584 hSetNewlineMode :: Handle -> NewlineMode -> IO ()
585 hSetNewlineMode handle NewlineMode{ inputNL=i, outputNL=o } =
586 withAllHandles__ "hSetNewlineMode" handle $ \h_@Handle__{..} ->
589 return h_{ haInputNL=i, haOutputNL=o }
591 -- -----------------------------------------------------------------------------
592 -- Duplicating a Handle
594 -- | Returns a duplicate of the original handle, with its own buffer.
595 -- The two Handles will share a file pointer, however. The original
596 -- handle's buffer is flushed, including discarding any input data,
597 -- before the handle is duplicated.
599 hDuplicate :: Handle -> IO Handle
600 hDuplicate h@(FileHandle path m) = do
601 withHandle_' "hDuplicate" h m $ \h_ ->
602 dupHandle path h Nothing h_ (Just handleFinalizer)
603 hDuplicate h@(DuplexHandle path r w) = do
604 write_side@(FileHandle _ write_m) <-
605 withHandle_' "hDuplicate" h w $ \h_ ->
606 dupHandle path h Nothing h_ (Just handleFinalizer)
607 read_side@(FileHandle _ read_m) <-
608 withHandle_' "hDuplicate" h r $ \h_ ->
609 dupHandle path h (Just write_m) h_ Nothing
610 return (DuplexHandle path read_m write_m)
612 dupHandle :: FilePath
614 -> Maybe (MVar Handle__)
616 -> Maybe HandleFinalizer
618 dupHandle filepath h other_side h_@Handle__{..} mb_finalizer = do
619 -- flush the buffer first, so we don't have to copy its contents
623 new_dev <- IODevice.dup haDevice
624 dupHandle_ new_dev filepath other_side h_ mb_finalizer
626 withHandle_' "dupHandle" h r $ \Handle__{haDevice=dev} -> do
627 dupHandle_ dev filepath other_side h_ mb_finalizer
629 dupHandle_ :: (IODevice dev, BufferedIO dev, Typeable dev) => dev
631 -> Maybe (MVar Handle__)
633 -> Maybe HandleFinalizer
635 dupHandle_ new_dev filepath other_side h_@Handle__{..} mb_finalizer = do
637 let mb_codec = if isJust haEncoder then Just localeEncoding else Nothing
638 mkHandle new_dev filepath haType True{-buffered-} mb_codec
639 NewlineMode { inputNL = haInputNL, outputNL = haOutputNL }
640 mb_finalizer other_side
642 -- -----------------------------------------------------------------------------
643 -- Replacing a Handle
646 Makes the second handle a duplicate of the first handle. The second
647 handle will be closed first, if it is not already.
649 This can be used to retarget the standard Handles, for example:
651 > do h <- openFile "mystdout" WriteMode
652 > hDuplicateTo h stdout
655 hDuplicateTo :: Handle -> Handle -> IO ()
656 hDuplicateTo h1@(FileHandle path m1) h2@(FileHandle _ m2) = do
657 withHandle__' "hDuplicateTo" h2 m2 $ \h2_ -> do
659 withHandle_' "hDuplicateTo" h1 m1 $ \h1_ -> do
660 dupHandleTo path h1 Nothing h2_ h1_ (Just handleFinalizer)
661 hDuplicateTo h1@(DuplexHandle path r1 w1) h2@(DuplexHandle _ r2 w2) = do
662 withHandle__' "hDuplicateTo" h2 w2 $ \w2_ -> do
664 withHandle_' "hDuplicateTo" h1 w1 $ \w1_ -> do
665 dupHandleTo path h1 Nothing w2_ w1_ (Just handleFinalizer)
666 withHandle__' "hDuplicateTo" h2 r2 $ \r2_ -> do
668 withHandle_' "hDuplicateTo" h1 r1 $ \r1_ -> do
669 dupHandleTo path h1 (Just w1) r2_ r1_ Nothing
671 ioe_dupHandlesNotCompatible h1
674 ioe_dupHandlesNotCompatible :: Handle -> IO a
675 ioe_dupHandlesNotCompatible h =
676 ioException (IOError (Just h) IllegalOperation "hDuplicateTo"
677 "handles are incompatible" Nothing Nothing)
679 dupHandleTo :: FilePath
681 -> Maybe (MVar Handle__)
684 -> Maybe HandleFinalizer
686 dupHandleTo filepath h other_side
687 hto_@Handle__{haDevice=devTo,..}
688 h_@Handle__{haDevice=dev} mb_finalizer = do
691 Nothing -> ioe_dupHandlesNotCompatible h
693 _ <- IODevice.dup2 dev dev'
694 FileHandle _ m <- dupHandle_ dev' filepath other_side h_ mb_finalizer
697 -- ---------------------------------------------------------------------------
700 -- | 'hShow' is in the 'IO' monad, and gives more comprehensive output
701 -- than the (pure) instance of 'Show' for 'Handle'.
703 hShow :: Handle -> IO String
704 hShow h@(FileHandle path _) = showHandle' path False h
705 hShow h@(DuplexHandle path _ _) = showHandle' path True h
707 showHandle' :: String -> Bool -> Handle -> IO String
708 showHandle' filepath is_duplex h =
709 withHandle_ "showHandle" h $ \hdl_ ->
711 showType | is_duplex = showString "duplex (read-write)"
712 | otherwise = shows (haType hdl_)
716 showHdl (haType hdl_)
717 (showString "loc=" . showString filepath . showChar ',' .
718 showString "type=" . showType . showChar ',' .
719 showString "buffering=" . showBufMode (unsafePerformIO (readIORef (haCharBuffer hdl_))) (haBufferMode hdl_) . showString "}" )
723 showHdl :: HandleType -> ShowS -> ShowS
726 ClosedHandle -> shows ht . showString "}"
729 showBufMode :: Buffer e -> BufferMode -> ShowS
730 showBufMode buf bmo =
732 NoBuffering -> showString "none"
733 LineBuffering -> showString "line"
734 BlockBuffering (Just n) -> showString "block " . showParen True (shows n)
735 BlockBuffering Nothing -> showString "block " . showParen True (shows def)