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 mb_exc1 <- hClose' h w
86 mb_exc2 <- hClose' h r
89 Just e -> hClose_maybethrow mb_exc2 h
91 hClose_maybethrow :: Maybe SomeException -> Handle -> IO ()
92 hClose_maybethrow Nothing h = return ()
93 hClose_maybethrow (Just e) h = hClose_rethrow e h
95 hClose_rethrow :: SomeException -> Handle -> IO ()
97 case fromException e of
98 Just ioe -> ioError (augmentIOError ioe "hClose" h)
101 hClose' :: Handle -> MVar Handle__ -> IO (Maybe SomeException)
102 hClose' h m = withHandle' "hClose" h m $ hClose_help
104 -----------------------------------------------------------------------------
105 -- Detecting and changing the size of a file
107 -- | For a handle @hdl@ which attached to a physical file,
108 -- 'hFileSize' @hdl@ returns the size of that file in 8-bit bytes.
110 hFileSize :: Handle -> IO Integer
112 withHandle_ "hFileSize" handle $ \ handle_@Handle__{haDevice=dev} -> do
113 case haType handle_ of
114 ClosedHandle -> ioe_closedHandle
115 SemiClosedHandle -> ioe_closedHandle
116 _ -> do flushWriteBuffer handle_
117 r <- IODevice.getSize dev
120 else ioException (IOError Nothing InappropriateType "hFileSize"
121 "not a regular file" Nothing Nothing)
124 -- | 'hSetFileSize' @hdl@ @size@ truncates the physical file with handle @hdl@ to @size@ bytes.
126 hSetFileSize :: Handle -> Integer -> IO ()
127 hSetFileSize handle size =
128 withHandle_ "hSetFileSize" handle $ \ handle_@Handle__{haDevice=dev} -> do
129 case haType handle_ of
130 ClosedHandle -> ioe_closedHandle
131 SemiClosedHandle -> ioe_closedHandle
132 _ -> do flushWriteBuffer handle_
133 IODevice.setSize dev size
136 -- ---------------------------------------------------------------------------
137 -- Detecting the End of Input
139 -- | For a readable handle @hdl@, 'hIsEOF' @hdl@ returns
140 -- 'True' if no further input can be taken from @hdl@ or for a
141 -- physical file, if the current I\/O position is equal to the length of
142 -- the file. Otherwise, it returns 'False'.
144 -- NOTE: 'hIsEOF' may block, because it has to attempt to read from
145 -- the stream to determine whether there is any more data to be read.
147 hIsEOF :: Handle -> IO Bool
148 hIsEOF handle = wantReadableHandle_ "hIsEOF" handle $ \Handle__{..} -> do
150 cbuf <- readIORef haCharBuffer
151 if not (isEmptyBuffer cbuf) then return False else do
153 bbuf <- readIORef haByteBuffer
154 if not (isEmptyBuffer bbuf) then return False else do
156 -- NB. do no decoding, just fill the byte buffer; see #3808
157 (r,bbuf') <- Buffered.fillReadBuffer haDevice bbuf
160 else do writeIORef haByteBuffer bbuf'
163 -- ---------------------------------------------------------------------------
166 -- | Computation 'hLookAhead' returns the next character from the handle
167 -- without removing it from the input buffer, blocking until a character
170 -- This operation may fail with:
172 -- * 'isEOFError' if the end of file has been reached.
174 hLookAhead :: Handle -> IO Char
176 wantReadableHandle_ "hLookAhead" handle hLookAhead_
178 -- ---------------------------------------------------------------------------
179 -- Buffering Operations
181 -- Three kinds of buffering are supported: line-buffering,
182 -- block-buffering or no-buffering. See GHC.IO.Handle for definition and
183 -- further explanation of what the type represent.
185 -- | Computation 'hSetBuffering' @hdl mode@ sets the mode of buffering for
186 -- handle @hdl@ on subsequent reads and writes.
188 -- If the buffer mode is changed from 'BlockBuffering' or
189 -- 'LineBuffering' to 'NoBuffering', then
191 -- * if @hdl@ is writable, the buffer is flushed as for 'hFlush';
193 -- * if @hdl@ is not writable, the contents of the buffer is discarded.
195 -- This operation may fail with:
197 -- * 'isPermissionError' if the handle has already been used for reading
198 -- or writing and the implementation does not allow the buffering mode
201 hSetBuffering :: Handle -> BufferMode -> IO ()
202 hSetBuffering handle mode =
203 withAllHandles__ "hSetBuffering" handle $ \ handle_@Handle__{..} -> do
205 ClosedHandle -> ioe_closedHandle
207 if mode == haBufferMode then return handle_ else do
209 -- See [note Buffer Sizing] in GHC.IO.Handle.Types
213 BlockBuffering (Just n) | n <= 0 -> ioe_bufsiz n
216 -- for input terminals we need to put the terminal into
217 -- cooked or raw mode depending on the type of buffering.
218 is_tty <- IODevice.isTerminal haDevice
219 when (is_tty && isReadableHandleType haType) $
221 #ifndef mingw32_HOST_OS
222 -- 'raw' mode under win32 is a bit too specialised (and troublesome
223 -- for most common uses), so simply disable its use here.
224 NoBuffering -> IODevice.setRaw haDevice True
226 NoBuffering -> return ()
228 _ -> IODevice.setRaw haDevice False
230 -- throw away spare buffers, they might be the wrong size
231 writeIORef haBuffers BufferListNil
233 return Handle__{ haBufferMode = mode,.. }
235 -- -----------------------------------------------------------------------------
238 -- | The action 'hSetEncoding' @hdl@ @encoding@ changes the text encoding
239 -- for the handle @hdl@ to @encoding@. The default encoding when a 'Handle' is
240 -- created is 'localeEncoding', namely the default encoding for the current
243 -- To create a 'Handle' with no encoding at all, use 'openBinaryFile'. To
244 -- stop further encoding or decoding on an existing 'Handle', use
247 -- 'hSetEncoding' may need to flush buffered data in order to change
250 hSetEncoding :: Handle -> TextEncoding -> IO ()
251 hSetEncoding hdl encoding = do
252 withAllHandles__ "hSetEncoding" hdl $ \h_@Handle__{..} -> do
255 openTextEncoding (Just encoding) haType $ \ mb_encoder mb_decoder -> do
256 bbuf <- readIORef haByteBuffer
257 ref <- newIORef (error "last_decode")
258 return (Handle__{ haLastDecode = ref,
259 haDecoder = mb_decoder,
260 haEncoder = mb_encoder,
261 haCodec = Just encoding, .. })
263 -- | Return the current 'TextEncoding' for the specified 'Handle', or
264 -- 'Nothing' if the 'Handle' is in binary mode.
266 -- Note that the 'TextEncoding' remembers nothing about the state of
267 -- the encoder/decoder in use on this 'Handle'. For example, if the
268 -- encoding in use is UTF-16, then using 'hGetEncoding' and
269 -- 'hSetEncoding' to save and restore the encoding may result in an
270 -- extra byte-order-mark being written to the file.
272 hGetEncoding :: Handle -> IO (Maybe TextEncoding)
274 withHandle_ "hGetEncoding" hdl $ \h_@Handle__{..} -> return haCodec
276 -- -----------------------------------------------------------------------------
279 -- | The action 'hFlush' @hdl@ causes any items buffered for output
280 -- in handle @hdl@ to be sent immediately to the operating system.
282 -- This operation may fail with:
284 -- * 'isFullError' if the device is full;
286 -- * 'isPermissionError' if a system resource limit would be exceeded.
287 -- It is unspecified whether the characters in the buffer are discarded
288 -- or retained under these circumstances.
290 hFlush :: Handle -> IO ()
291 hFlush handle = wantWritableHandle "hFlush" handle flushWriteBuffer
293 -- | The action 'hFlushAll' @hdl@ flushes all buffered data in @hdl@,
294 -- including any buffered read data. Buffered read data is flushed
295 -- by seeking the file position back to the point before the bufferred
296 -- data was read, and hence only works if @hdl@ is seekable (see
299 -- This operation may fail with:
301 -- * 'isFullError' if the device is full;
303 -- * 'isPermissionError' if a system resource limit would be exceeded.
304 -- It is unspecified whether the characters in the buffer are discarded
305 -- or retained under these circumstances;
307 -- * 'isIllegalOperation' if @hdl@ has buffered read data, and is not
310 hFlushAll :: Handle -> IO ()
311 hFlushAll handle = withHandle_ "hFlushAll" handle flushBuffer
313 -- -----------------------------------------------------------------------------
314 -- Repositioning Handles
316 data HandlePosn = HandlePosn Handle HandlePosition
318 instance Eq HandlePosn where
319 (HandlePosn h1 p1) == (HandlePosn h2 p2) = p1==p2 && h1==h2
321 instance Show HandlePosn where
322 showsPrec p (HandlePosn h pos) =
323 showsPrec p h . showString " at position " . shows pos
325 -- HandlePosition is the Haskell equivalent of POSIX' off_t.
326 -- We represent it as an Integer on the Haskell side, but
327 -- cheat slightly in that hGetPosn calls upon a C helper
328 -- that reports the position back via (merely) an Int.
329 type HandlePosition = Integer
331 -- | Computation 'hGetPosn' @hdl@ returns the current I\/O position of
332 -- @hdl@ as a value of the abstract type 'HandlePosn'.
334 hGetPosn :: Handle -> IO HandlePosn
337 return (HandlePosn handle posn)
339 -- | If a call to 'hGetPosn' @hdl@ returns a position @p@,
340 -- then computation 'hSetPosn' @p@ sets the position of @hdl@
341 -- to the position it held at the time of the call to 'hGetPosn'.
343 -- This operation may fail with:
345 -- * 'isPermissionError' if a system resource limit would be exceeded.
347 hSetPosn :: HandlePosn -> IO ()
348 hSetPosn (HandlePosn h i) = hSeek h AbsoluteSeek i
350 -- ---------------------------------------------------------------------------
354 - when seeking using `SeekFromEnd', positive offsets (>=0) means
355 seeking at or past EOF.
357 - we possibly deviate from the report on the issue of seeking within
358 the buffer and whether to flush it or not. The report isn't exactly
362 -- | Computation 'hSeek' @hdl mode i@ sets the position of handle
363 -- @hdl@ depending on @mode@.
364 -- The offset @i@ is given in terms of 8-bit bytes.
366 -- If @hdl@ is block- or line-buffered, then seeking to a position which is not
367 -- in the current buffer will first cause any items in the output buffer to be
368 -- written to the device, and then cause the input buffer to be discarded.
369 -- Some handles may not be seekable (see 'hIsSeekable'), or only support a
370 -- subset of the possible positioning operations (for instance, it may only
371 -- be possible to seek to the end of a tape, or to a positive offset from
372 -- the beginning or current position).
373 -- It is not possible to set a negative I\/O position, or for
374 -- a physical file, an I\/O position beyond the current end-of-file.
376 -- This operation may fail with:
378 -- * 'isIllegalOperationError' if the Handle is not seekable, or does
379 -- not support the requested seek mode.
381 -- * 'isPermissionError' if a system resource limit would be exceeded.
383 hSeek :: Handle -> SeekMode -> Integer -> IO ()
384 hSeek handle mode offset =
385 wantSeekableHandle "hSeek" handle $ \ handle_@Handle__{..} -> do
386 debugIO ("hSeek " ++ show (mode,offset))
387 buf <- readIORef haCharBuffer
390 then do flushWriteBuffer handle_
391 IODevice.seek haDevice mode offset
394 let r = bufL buf; w = bufR buf
395 if mode == RelativeSeek && isNothing haDecoder &&
396 offset >= 0 && offset < fromIntegral (w - r)
397 then writeIORef haCharBuffer buf{ bufL = r + fromIntegral offset }
400 flushCharReadBuffer handle_
401 flushByteReadBuffer handle_
402 IODevice.seek haDevice mode offset
405 -- | Computation 'hTell' @hdl@ returns the current position of the
406 -- handle @hdl@, as the number of bytes from the beginning of
407 -- the file. The value returned may be subsequently passed to
408 -- 'hSeek' to reposition the handle to the current position.
410 -- This operation may fail with:
412 -- * 'isIllegalOperationError' if the Handle is not seekable.
414 hTell :: Handle -> IO Integer
416 wantSeekableHandle "hGetPosn" handle $ \ handle_@Handle__{..} -> do
418 posn <- IODevice.tell haDevice
420 -- we can't tell the real byte offset if there are buffered
421 -- Chars, so must flush first:
422 flushCharBuffer handle_
424 bbuf <- readIORef haByteBuffer
427 | isWriteBuffer bbuf = posn + fromIntegral (bufferElems bbuf)
428 | otherwise = posn - fromIntegral (bufferElems bbuf)
430 cbuf <- readIORef haCharBuffer
431 debugIO ("\nhGetPosn: (posn, real_posn) = " ++ show (posn, real_posn))
432 debugIO (" cbuf: " ++ summaryBuffer cbuf ++
433 " bbuf: " ++ summaryBuffer bbuf)
437 -- -----------------------------------------------------------------------------
440 -- A number of operations return information about the properties of a
441 -- handle. Each of these operations returns `True' if the handle has
442 -- the specified property, and `False' otherwise.
444 hIsOpen :: Handle -> IO Bool
446 withHandle_ "hIsOpen" handle $ \ handle_ -> do
447 case haType handle_ of
448 ClosedHandle -> return False
449 SemiClosedHandle -> return False
452 hIsClosed :: Handle -> IO Bool
454 withHandle_ "hIsClosed" handle $ \ handle_ -> do
455 case haType handle_ of
456 ClosedHandle -> return True
459 {- not defined, nor exported, but mentioned
460 here for documentation purposes:
462 hSemiClosed :: Handle -> IO Bool
466 return (not (ho || hc))
469 hIsReadable :: Handle -> IO Bool
470 hIsReadable (DuplexHandle _ _ _) = return True
472 withHandle_ "hIsReadable" handle $ \ handle_ -> do
473 case haType handle_ of
474 ClosedHandle -> ioe_closedHandle
475 SemiClosedHandle -> ioe_closedHandle
476 htype -> return (isReadableHandleType htype)
478 hIsWritable :: Handle -> IO Bool
479 hIsWritable (DuplexHandle _ _ _) = return True
481 withHandle_ "hIsWritable" handle $ \ handle_ -> do
482 case haType handle_ of
483 ClosedHandle -> ioe_closedHandle
484 SemiClosedHandle -> ioe_closedHandle
485 htype -> return (isWritableHandleType htype)
487 -- | Computation 'hGetBuffering' @hdl@ returns the current buffering mode
490 hGetBuffering :: Handle -> IO BufferMode
491 hGetBuffering handle =
492 withHandle_ "hGetBuffering" handle $ \ handle_ -> do
493 case haType handle_ of
494 ClosedHandle -> ioe_closedHandle
496 -- We're being non-standard here, and allow the buffering
497 -- of a semi-closed handle to be queried. -- sof 6/98
498 return (haBufferMode handle_) -- could be stricter..
500 hIsSeekable :: Handle -> IO Bool
502 withHandle_ "hIsSeekable" handle $ \ handle_@Handle__{..} -> do
504 ClosedHandle -> ioe_closedHandle
505 SemiClosedHandle -> ioe_closedHandle
506 AppendHandle -> return False
507 _ -> IODevice.isSeekable haDevice
509 -- -----------------------------------------------------------------------------
510 -- Changing echo status (Non-standard GHC extensions)
512 -- | Set the echoing status of a handle connected to a terminal.
514 hSetEcho :: Handle -> Bool -> IO ()
515 hSetEcho handle on = do
516 isT <- hIsTerminalDevice handle
520 withHandle_ "hSetEcho" handle $ \ Handle__{..} -> do
522 ClosedHandle -> ioe_closedHandle
523 _ -> IODevice.setEcho haDevice on
525 -- | Get the echoing status of a handle connected to a terminal.
527 hGetEcho :: Handle -> IO Bool
529 isT <- hIsTerminalDevice handle
533 withHandle_ "hGetEcho" handle $ \ Handle__{..} -> do
535 ClosedHandle -> ioe_closedHandle
536 _ -> IODevice.getEcho haDevice
538 -- | Is the handle connected to a terminal?
540 hIsTerminalDevice :: Handle -> IO Bool
541 hIsTerminalDevice handle = do
542 withHandle_ "hIsTerminalDevice" handle $ \ Handle__{..} -> do
544 ClosedHandle -> ioe_closedHandle
545 _ -> IODevice.isTerminal haDevice
547 -- -----------------------------------------------------------------------------
550 -- | Select binary mode ('True') or text mode ('False') on a open handle.
551 -- (See also 'openBinaryFile'.)
553 -- This has the same effect as calling 'hSetEncoding' with 'latin1', together
554 -- with 'hSetNewlineMode' with 'noNewlineTranslation'.
556 hSetBinaryMode :: Handle -> Bool -> IO ()
557 hSetBinaryMode handle bin =
558 withAllHandles__ "hSetBinaryMode" handle $ \ h_@Handle__{..} ->
563 let mb_te | bin = Nothing
564 | otherwise = Just localeEncoding
566 openTextEncoding mb_te haType $ \ mb_encoder mb_decoder -> do
568 -- should match the default newline mode, whatever that is
569 let nl | bin = noNewlineTranslation
570 | otherwise = nativeNewlineMode
572 bbuf <- readIORef haByteBuffer
573 ref <- newIORef (error "codec_state", bbuf)
575 return Handle__{ haLastDecode = ref,
576 haEncoder = mb_encoder,
577 haDecoder = mb_decoder,
579 haInputNL = inputNL nl,
580 haOutputNL = outputNL nl, .. }
582 -- -----------------------------------------------------------------------------
585 -- | Set the 'NewlineMode' on the specified 'Handle'. All buffered
586 -- data is flushed first.
587 hSetNewlineMode :: Handle -> NewlineMode -> IO ()
588 hSetNewlineMode handle NewlineMode{ inputNL=i, outputNL=o } =
589 withAllHandles__ "hSetNewlineMode" handle $ \h_@Handle__{..} ->
592 return h_{ haInputNL=i, haOutputNL=o }
594 -- -----------------------------------------------------------------------------
595 -- Duplicating a Handle
597 -- | Returns a duplicate of the original handle, with its own buffer.
598 -- The two Handles will share a file pointer, however. The original
599 -- handle's buffer is flushed, including discarding any input data,
600 -- before the handle is duplicated.
602 hDuplicate :: Handle -> IO Handle
603 hDuplicate h@(FileHandle path m) = do
604 withHandle_' "hDuplicate" h m $ \h_ ->
605 dupHandle path h Nothing h_ (Just handleFinalizer)
606 hDuplicate h@(DuplexHandle path r w) = do
607 write_side@(FileHandle _ write_m) <-
608 withHandle_' "hDuplicate" h w $ \h_ ->
609 dupHandle path h Nothing h_ (Just handleFinalizer)
610 read_side@(FileHandle _ read_m) <-
611 withHandle_' "hDuplicate" h r $ \h_ ->
612 dupHandle path h (Just write_m) h_ Nothing
613 return (DuplexHandle path read_m write_m)
615 dupHandle :: FilePath
617 -> Maybe (MVar Handle__)
619 -> Maybe HandleFinalizer
621 dupHandle filepath h other_side h_@Handle__{..} mb_finalizer = do
622 -- flush the buffer first, so we don't have to copy its contents
626 new_dev <- IODevice.dup haDevice
627 dupHandle_ new_dev filepath other_side h_ mb_finalizer
629 withHandle_' "dupHandle" h r $ \Handle__{haDevice=dev} -> do
630 dupHandle_ dev filepath other_side h_ mb_finalizer
632 dupHandle_ :: (IODevice dev, BufferedIO dev, Typeable dev) => dev
634 -> Maybe (MVar Handle__)
636 -> Maybe HandleFinalizer
638 dupHandle_ new_dev filepath other_side h_@Handle__{..} mb_finalizer = do
640 let mb_codec = if isJust haEncoder then Just localeEncoding else Nothing
641 mkHandle new_dev filepath haType True{-buffered-} mb_codec
642 NewlineMode { inputNL = haInputNL, outputNL = haOutputNL }
643 mb_finalizer other_side
645 -- -----------------------------------------------------------------------------
646 -- Replacing a Handle
649 Makes the second handle a duplicate of the first handle. The second
650 handle will be closed first, if it is not already.
652 This can be used to retarget the standard Handles, for example:
654 > do h <- openFile "mystdout" WriteMode
655 > hDuplicateTo h stdout
658 hDuplicateTo :: Handle -> Handle -> IO ()
659 hDuplicateTo h1@(FileHandle path m1) h2@(FileHandle _ m2) = do
660 withHandle__' "hDuplicateTo" h2 m2 $ \h2_ -> do
662 withHandle_' "hDuplicateTo" h1 m1 $ \h1_ -> do
663 dupHandleTo path h1 Nothing h2_ h1_ (Just handleFinalizer)
664 hDuplicateTo h1@(DuplexHandle path r1 w1) h2@(DuplexHandle _ r2 w2) = do
665 withHandle__' "hDuplicateTo" h2 w2 $ \w2_ -> do
667 withHandle_' "hDuplicateTo" h1 w1 $ \w1_ -> do
668 dupHandleTo path h1 Nothing w2_ w1_ (Just handleFinalizer)
669 withHandle__' "hDuplicateTo" h2 r2 $ \r2_ -> do
671 withHandle_' "hDuplicateTo" h1 r1 $ \r1_ -> do
672 dupHandleTo path h1 (Just w1) r2_ r1_ Nothing
674 ioe_dupHandlesNotCompatible h1
677 ioe_dupHandlesNotCompatible :: Handle -> IO a
678 ioe_dupHandlesNotCompatible h =
679 ioException (IOError (Just h) IllegalOperation "hDuplicateTo"
680 "handles are incompatible" Nothing Nothing)
682 dupHandleTo :: FilePath
684 -> Maybe (MVar Handle__)
687 -> Maybe HandleFinalizer
689 dupHandleTo filepath h other_side
690 hto_@Handle__{haDevice=devTo,..}
691 h_@Handle__{haDevice=dev} mb_finalizer = do
694 Nothing -> ioe_dupHandlesNotCompatible h
696 _ <- IODevice.dup2 dev dev'
697 FileHandle _ m <- dupHandle_ dev' filepath other_side h_ mb_finalizer
700 -- ---------------------------------------------------------------------------
703 -- | 'hShow' is in the 'IO' monad, and gives more comprehensive output
704 -- than the (pure) instance of 'Show' for 'Handle'.
706 hShow :: Handle -> IO String
707 hShow h@(FileHandle path _) = showHandle' path False h
708 hShow h@(DuplexHandle path _ _) = showHandle' path True h
710 showHandle' :: String -> Bool -> Handle -> IO String
711 showHandle' filepath is_duplex h =
712 withHandle_ "showHandle" h $ \hdl_ ->
714 showType | is_duplex = showString "duplex (read-write)"
715 | otherwise = shows (haType hdl_)
719 showHdl (haType hdl_)
720 (showString "loc=" . showString filepath . showChar ',' .
721 showString "type=" . showType . showChar ',' .
722 showString "buffering=" . showBufMode (unsafePerformIO (readIORef (haCharBuffer hdl_))) (haBufferMode hdl_) . showString "}" )
726 showHdl :: HandleType -> ShowS -> ShowS
729 ClosedHandle -> shows ht . showString "}"
732 showBufMode :: Buffer e -> BufferMode -> ShowS
733 showBufMode buf bmo =
735 NoBuffering -> showString "none"
736 LineBuffering -> showString "line"
737 BlockBuffering (Just n) -> showString "block " . showParen True (shows n)
738 BlockBuffering Nothing -> showString "block " . showParen True (shows def)