| Copyright | (c) The University of Glasgow 1994-2009 | 
|---|---|
| License | see libraries/base/LICENSE | 
| Maintainer | libraries@haskell.org | 
| Stability | provisional | 
| Portability | non-portable | 
| Safe Haskell | Trustworthy | 
| Language | Haskell2010 | 
GHC.IO.Handle
Description
External API for GHC's Handle implementation
Synopsis
- data Handle
- data BufferMode
- mkFileHandle :: (RawIO dev, IODevice dev, BufferedIO dev, Typeable dev) => dev -> FilePath -> IOMode -> Maybe TextEncoding -> NewlineMode -> IO Handle
- mkDuplexHandle :: (RawIO dev, IODevice dev, BufferedIO dev, Typeable dev) => dev -> FilePath -> Maybe TextEncoding -> NewlineMode -> IO Handle
- hFileSize :: Handle -> IO Integer
- hSetFileSize :: Handle -> Integer -> IO ()
- hIsEOF :: Handle -> IO Bool
- isEOF :: IO Bool
- hLookAhead :: Handle -> IO Char
- hSetBuffering :: Handle -> BufferMode -> IO ()
- hSetBinaryMode :: Handle -> Bool -> IO ()
- hSetEncoding :: Handle -> TextEncoding -> IO ()
- hGetEncoding :: Handle -> IO (Maybe TextEncoding)
- hFlush :: Handle -> IO ()
- hFlushAll :: Handle -> IO ()
- hDuplicate :: Handle -> IO Handle
- hDuplicateTo :: Handle -> Handle -> IO ()
- hClose :: Handle -> IO ()
- hClose_help :: Handle__ -> IO (Handle__, Maybe SomeException)
- data LockMode
- hLock :: Handle -> LockMode -> IO ()
- hTryLock :: Handle -> LockMode -> IO Bool
- type HandlePosition = Integer
- data HandlePosn = HandlePosn Handle HandlePosition
- hGetPosn :: Handle -> IO HandlePosn
- hSetPosn :: HandlePosn -> IO ()
- data SeekMode
- hSeek :: Handle -> SeekMode -> Integer -> IO ()
- hTell :: Handle -> IO Integer
- hIsOpen :: Handle -> IO Bool
- hIsClosed :: Handle -> IO Bool
- hIsReadable :: Handle -> IO Bool
- hIsWritable :: Handle -> IO Bool
- hGetBuffering :: Handle -> IO BufferMode
- hIsSeekable :: Handle -> IO Bool
- hSetEcho :: Handle -> Bool -> IO ()
- hGetEcho :: Handle -> IO Bool
- hIsTerminalDevice :: Handle -> IO Bool
- hSetNewlineMode :: Handle -> NewlineMode -> IO ()
- data Newline
- data NewlineMode = NewlineMode {}
- nativeNewline :: Newline
- noNewlineTranslation :: NewlineMode
- universalNewlineMode :: NewlineMode
- nativeNewlineMode :: NewlineMode
- hShow :: Handle -> IO String
- hWaitForInput :: Handle -> Int -> IO Bool
- hGetChar :: Handle -> IO Char
- hGetLine :: Handle -> IO String
- hGetContents :: Handle -> IO String
- hGetContents' :: Handle -> IO String
- hPutChar :: Handle -> Char -> IO ()
- hPutStr :: Handle -> String -> IO ()
- hGetBuf :: Handle -> Ptr a -> Int -> IO Int
- hGetBufNonBlocking :: Handle -> Ptr a -> Int -> IO Int
- hPutBuf :: Handle -> Ptr a -> Int -> IO ()
- hPutBufNonBlocking :: Handle -> Ptr a -> Int -> IO Int
Documentation
Haskell defines operations to read and write characters from and to files,
 represented by values of type Handle.  Each value of this type is a
 handle: a record used by the Haskell run-time system to manage I/O
 with file system objects.  A handle has at least the following properties:
- whether it manages input or output or both;
- whether it is open, closed or semi-closed;
- whether the object is seekable;
- whether buffering is disabled, or enabled on a line or block basis;
- a buffer (whose length may be zero).
Most handles will also have a current I/O position indicating where the next
 input or output operation will occur.  A handle is readable if it
 manages only input or both input and output; likewise, it is writable if
 it manages only output or both input and output.  A handle is open when
 first allocated.
 Once it is closed it can no longer be used for either input or output,
 though an implementation cannot re-use its storage while references
 remain to it.  Handles are in the Show and Eq classes.  The string
 produced by showing a handle is system dependent; it should include
 enough information to identify the handle for debugging.  A handle is
 equal according to == only to itself; no attempt
 is made to compare the internal state of different handles for equality.
data BufferMode #
Three kinds of buffering are supported: line-buffering, block-buffering or no-buffering. These modes have the following effects. For output, items are written out, or flushed, from the internal buffer according to the buffer mode:
- line-buffering: the entire output buffer is flushed
    whenever a newline is output, the buffer overflows,
    a hFlushis issued, or the handle is closed.
- block-buffering: the entire buffer is written out whenever it
    overflows, a hFlushis issued, or the handle is closed.
- no-buffering: output is written immediately, and never stored in the buffer.
An implementation is free to flush the buffer more frequently, but not less frequently, than specified above. The output buffer is emptied as soon as it has been written out.
Similarly, input occurs according to the buffer mode for the handle:
- line-buffering: when the buffer for the handle is not empty, the next item is obtained from the buffer; otherwise, when the buffer is empty, characters up to and including the next newline character are read into the buffer. No characters are available until the newline character is available or the buffer is full.
- block-buffering: when the buffer for the handle becomes empty, the next block of data is read into the buffer.
- no-buffering: the next input item is read and returned.
    The hLookAheadoperation implies that even a no-buffered handle may require a one-character buffer.
The default buffering mode when a handle is opened is implementation-dependent and may depend on the file system object which is attached to that handle. For most implementations, physical files will normally be block-buffered and terminals will normally be line-buffered.
Constructors
| NoBuffering | buffering is disabled if possible. | 
| LineBuffering | line-buffering should be enabled if possible. | 
| BlockBuffering (Maybe Int) | block-buffering should be enabled if possible.
 The size of the buffer is  | 
Instances
Arguments
| :: (RawIO dev, IODevice dev, BufferedIO dev, Typeable dev) | |
| => dev | the underlying IO device, which must support
  | 
| -> FilePath | a string describing the  | 
| -> IOMode | |
| -> Maybe TextEncoding | |
| -> NewlineMode | |
| -> IO Handle | 
makes a new Handle
mkDuplexHandle :: (RawIO dev, IODevice dev, BufferedIO dev, Typeable dev) => dev -> FilePath -> Maybe TextEncoding -> NewlineMode -> IO Handle #
like mkFileHandle, except that a Handle is created with two
 independent buffers, one for reading and one for writing.  Used for
 full-duplex streams, such as network sockets.
hFileSize :: Handle -> IO Integer #
For a handle hdl which attached to a physical file,
 hFileSize hdl returns the size of that file in 8-bit bytes.
hSetFileSize :: Handle -> Integer -> IO () #
hSetFileSize hdl size truncates the physical file with handle hdl to size bytes.
For a readable handle hdl, hIsEOF hdl returns
 True if no further input can be taken from hdl or for a
 physical file, if the current I/O position is equal to the length of
 the file.  Otherwise, it returns False.
NOTE: hIsEOF may block, because it has to attempt to read from
 the stream to determine whether there is any more data to be read.
hLookAhead :: Handle -> IO Char #
Computation hLookAhead returns the next character from the handle
 without removing it from the input buffer, blocking until a character
 is available.
This operation may fail with:
- isEOFErrorif the end of file has been reached.
hSetBuffering :: Handle -> BufferMode -> IO () #
Computation hSetBuffering hdl mode sets the mode of buffering for
 handle hdl on subsequent reads and writes.
If the buffer mode is changed from BlockBuffering or
 LineBuffering to NoBuffering, then
- if hdlis writable, the buffer is flushed as forhFlush;
- if hdlis not writable, the contents of the buffer is discarded.
This operation may fail with:
- isPermissionErrorif the handle has already been used for reading or writing and the implementation does not allow the buffering mode to be changed.
hSetBinaryMode :: Handle -> Bool -> IO () #
Select binary mode (True) or text mode (False) on a open handle.
 (See also openBinaryFile.)
This has the same effect as calling hSetEncoding with char8, together
 with hSetNewlineMode with noNewlineTranslation.
hSetEncoding :: Handle -> TextEncoding -> IO () #
The action hSetEncoding hdl encoding changes the text encoding
 for the handle hdl to encoding.  The default encoding when a Handle is
 created is localeEncoding, namely the default encoding for the
 current locale.
To create a Handle with no encoding at all, use openBinaryFile.  To
 stop further encoding or decoding on an existing Handle, use
 hSetBinaryMode.
hSetEncoding may need to flush buffered data in order to change
 the encoding.
hGetEncoding :: Handle -> IO (Maybe TextEncoding) #
Return the current TextEncoding for the specified Handle, or
 Nothing if the Handle is in binary mode.
Note that the TextEncoding remembers nothing about the state of
 the encoder/decoder in use on this Handle.  For example, if the
 encoding in use is UTF-16, then using hGetEncoding and
 hSetEncoding to save and restore the encoding may result in an
 extra byte-order-mark being written to the file.
The action hFlush hdl causes any items buffered for output
 in handle hdl to be sent immediately to the operating system.
This operation may fail with:
- isFullErrorif the device is full;
- isPermissionErrorif a system resource limit would be exceeded. It is unspecified whether the characters in the buffer are discarded or retained under these circumstances.
hFlushAll :: Handle -> IO () #
The action hFlushAll hdl flushes all buffered data in hdl,
 including any buffered read data.  Buffered read data is flushed
 by seeking the file position back to the point before the bufferred
 data was read, and hence only works if hdl is seekable (see
 hIsSeekable).
This operation may fail with:
- isFullErrorif the device is full;
- isPermissionErrorif a system resource limit would be exceeded. It is unspecified whether the characters in the buffer are discarded or retained under these circumstances;
- isIllegalOperationif- hdlhas buffered read data, and is not seekable.
hDuplicate :: Handle -> IO Handle #
Returns a duplicate of the original handle, with its own buffer. The two Handles will share a file pointer, however. The original handle's buffer is flushed, including discarding any input data, before the handle is duplicated.
hDuplicateTo :: Handle -> Handle -> IO () #
Makes the second handle a duplicate of the first handle. The second handle will be closed first, if it is not already.
This can be used to retarget the standard Handles, for example:
do h <- openFile "mystdout" WriteMode hDuplicateTo h stdout
Computation hClose hdl makes handle hdl closed.  Before the
 computation finishes, if hdl is writable its buffer is flushed as
 for hFlush.
 Performing hClose on a handle that has already been closed has no effect;
 doing so is not an error.  All other operations on a closed handle will fail.
 If hClose fails for any reason, any further operations (apart from
 hClose) on the handle will still fail as if hdl had been successfully
 closed.
hClose_help :: Handle__ -> IO (Handle__, Maybe SomeException) #
Indicates a mode in which a file should be locked.
Constructors
| SharedLock | |
| ExclusiveLock | 
hLock :: Handle -> LockMode -> IO () #
If a Handle references a file descriptor, attempt to lock contents of the
 underlying file in appropriate mode. If the file is already locked in
 incompatible mode, this function blocks until the lock is established. The
 lock is automatically released upon closing a Handle.
Things to be aware of:
1) This function may block inside a C call. If it does, in order to be able to interrupt it with asynchronous exceptions and/or for other threads to continue working, you MUST use threaded version of the runtime system.
2) The implementation uses LockFileEx on Windows and flock otherwise,
 hence all of their caveats also apply here.
3) On non-Windows platforms that don't support flock (e.g. Solaris) this
 function throws FileLockingNotImplemented. We deliberately choose to not
 provide fcntl based locking instead because of its broken semantics.
Since: base-4.10.0.0
type HandlePosition = Integer #
data HandlePosn #
Constructors
| HandlePosn Handle HandlePosition | 
Instances
| Show HandlePosn # | Since: base-4.1.0.0 | 
| Defined in GHC.IO.Handle Methods showsPrec :: Int -> HandlePosn -> ShowS # show :: HandlePosn -> String # showList :: [HandlePosn] -> ShowS # | |
| Eq HandlePosn # | Since: base-4.1.0.0 | 
| Defined in GHC.IO.Handle Methods (==) :: HandlePosn -> HandlePosn -> Bool Source # (/=) :: HandlePosn -> HandlePosn -> Bool Source # | |
hGetPosn :: Handle -> IO HandlePosn #
Computation hGetPosn hdl returns the current I/O position of
 hdl as a value of the abstract type HandlePosn.
hSetPosn :: HandlePosn -> IO () #
If a call to hGetPosn hdl returns a position p,
 then computation hSetPosn p sets the position of hdl
 to the position it held at the time of the call to hGetPosn.
This operation may fail with:
- isPermissionErrorif a system resource limit would be exceeded.
A mode that determines the effect of hSeek hdl mode i.
Constructors
| AbsoluteSeek | the position of  | 
| RelativeSeek | the position of  | 
| SeekFromEnd | the position of  | 
Instances
| Enum SeekMode # | Since: base-4.2.0.0 | 
| Ix SeekMode # | Since: base-4.2.0.0 | 
| Defined in GHC.IO.Device Methods range :: (SeekMode, SeekMode) -> [SeekMode] # index :: (SeekMode, SeekMode) -> SeekMode -> Int # unsafeIndex :: (SeekMode, SeekMode) -> SeekMode -> Int # inRange :: (SeekMode, SeekMode) -> SeekMode -> Bool # rangeSize :: (SeekMode, SeekMode) -> Int # unsafeRangeSize :: (SeekMode, SeekMode) -> Int # | |
| Read SeekMode # | Since: base-4.2.0.0 | 
| Show SeekMode # | Since: base-4.2.0.0 | 
| Eq SeekMode # | Since: base-4.2.0.0 | 
| Ord SeekMode # | Since: base-4.2.0.0 | 
| Defined in GHC.IO.Device | |
hSeek :: Handle -> SeekMode -> Integer -> IO () #
Computation hSeek hdl mode i sets the position of handle
 hdl depending on mode.
 The offset i is given in terms of 8-bit bytes.
If hdl is block- or line-buffered, then seeking to a position which is not
 in the current buffer will first cause any items in the output buffer to be
 written to the device, and then cause the input buffer to be discarded.
 Some handles may not be seekable (see hIsSeekable), or only support a
 subset of the possible positioning operations (for instance, it may only
 be possible to seek to the end of a tape, or to a positive offset from
 the beginning or current position).
 It is not possible to set a negative I/O position, or for
 a physical file, an I/O position beyond the current end-of-file.
This operation may fail with:
- isIllegalOperationErrorif the Handle is not seekable, or does not support the requested seek mode.
- isPermissionErrorif a system resource limit would be exceeded.
hTell :: Handle -> IO Integer #
Computation hTell hdl returns the current position of the
 handle hdl, as the number of bytes from the beginning of
 the file.  The value returned may be subsequently passed to
 hSeek to reposition the handle to the current position.
This operation may fail with:
- isIllegalOperationErrorif the Handle is not seekable.
hIsReadable :: Handle -> IO Bool #
hIsWritable :: Handle -> IO Bool #
hGetBuffering :: Handle -> IO BufferMode #
Computation hGetBuffering hdl returns the current buffering mode
 for hdl.
hIsSeekable :: Handle -> IO Bool #
hIsTerminalDevice :: Handle -> IO Bool #
Is the handle connected to a terminal?
hSetNewlineMode :: Handle -> NewlineMode -> IO () #
Set the NewlineMode on the specified Handle.  All buffered
 data is flushed first.
The representation of a newline in the external file or stream.
Instances
| Read Newline # | Since: base-4.3.0.0 | 
| Show Newline # | Since: base-4.3.0.0 | 
| Eq Newline # | Since: base-4.2.0.0 | 
| Ord Newline # | Since: base-4.3.0.0 | 
| Defined in GHC.IO.Handle.Types | |
data NewlineMode #
Specifies the translation, if any, of newline characters between
 internal Strings and the external file or stream.  Haskell Strings
 are assumed to represent newlines with the '\n' character; the
 newline mode specifies how to translate '\n' on output, and what to
 translate into '\n' on input.
Constructors
| NewlineMode | |
Instances
noNewlineTranslation :: NewlineMode #
Do no newline translation at all.
noNewlineTranslation  = NewlineMode { inputNL  = LF, outputNL = LF }universalNewlineMode :: NewlineMode #
Map '\r\n' into '\n' on input, and '\n' to the native newline
 representation on output.  This mode can be used on any platform, and
 works with text files using any newline convention.  The downside is
 that readFile >>= writeFile might yield a different file.
universalNewlineMode  = NewlineMode { inputNL  = CRLF,
                                      outputNL = nativeNewline }nativeNewlineMode :: NewlineMode #
Use the native newline representation on both input and output
nativeNewlineMode  = NewlineMode { inputNL  = nativeNewline
                                   outputNL = nativeNewline }hWaitForInput :: Handle -> Int -> IO Bool #
Computation hWaitForInput hdl t
 waits until input is available on handle hdl.
 It returns True as soon as input is available on hdl,
 or False if no input is available within t milliseconds.  Note that
 hWaitForInput waits until one or more full characters are available,
 which means that it needs to do decoding, and hence may fail
 with a decoding error.
If t is less than zero, then hWaitForInput waits indefinitely.
This operation may fail with:
- isEOFErrorif the end of file has been reached.
- a decoding error, if the input begins with an invalid byte sequence in this Handle's encoding.
NOTE for GHC users: unless you use the -threaded flag,
 hWaitForInput hdl t where t >= 0 will block all other Haskell
 threads for the duration of the call.  It behaves like a
 safe foreign call in this respect.
hGetChar :: Handle -> IO Char #
Computation hGetChar hdl reads a character from the file or
 channel managed by hdl, blocking until a character is available.
This operation may fail with:
- isEOFErrorif the end of file has been reached.
hGetLine :: Handle -> IO String #
Computation hGetLine hdl reads a line from the file or
 channel managed by hdl.
This operation may fail with:
- isEOFErrorif the end of file is encountered when reading the first character of the line.
If hGetLine encounters end-of-file at any other point while reading
 in a line, it is treated as a line terminator and the (partial)
 line is returned.
hGetContents :: Handle -> IO String #
Computation hGetContents hdl returns the list of characters
 corresponding to the unread portion of the channel or file managed
 by hdl, which is put into an intermediate state, semi-closed.
 In this state, hdl is effectively closed,
 but items are read from hdl on demand and accumulated in a special
 list returned by hGetContents hdl.
Any operation that fails because a handle is closed,
 also fails if a handle is semi-closed.  The only exception is
 hClose.  A semi-closed handle becomes closed:
- if hCloseis applied to it;
- if an I/O error occurs when reading an item from the handle;
- or once the entire contents of the handle has been read.
Once a semi-closed handle becomes closed, the contents of the associated list becomes fixed. The contents of this final list is only partially specified: it will contain at least all the items of the stream that were evaluated prior to the handle becoming closed.
Any I/O errors encountered while a handle is semi-closed are simply discarded.
This operation may fail with:
- isEOFErrorif the end of file has been reached.
hGetContents' :: Handle -> IO String #
The hGetContents' operation reads all input on the given handle
 before returning it as a String and closing the handle.
Since: base-4.15.0.0
hPutChar :: Handle -> Char -> IO () #
Computation hPutChar hdl ch writes the character ch to the
 file or channel managed by hdl.  Characters may be buffered if
 buffering is enabled for hdl.
This operation may fail with:
- isFullErrorif the device is full; or
- isPermissionErrorif another system resource limit would be exceeded.
hPutStr :: Handle -> String -> IO () #
Computation hPutStr hdl s writes the string
 s to the file or channel managed by hdl.
This operation may fail with:
- isFullErrorif the device is full; or
- isPermissionErrorif another system resource limit would be exceeded.
hGetBuf :: Handle -> Ptr a -> Int -> IO Int #
hGetBuf hdl buf count reads data from the handle hdl
 into the buffer buf until either EOF is reached or
 count 8-bit bytes have been read.
 It returns the number of bytes actually read.  This may be zero if
 EOF was reached before any data was read (or if count is zero).
hGetBuf never raises an EOF exception, instead it returns a value
 smaller than count.
If the handle is a pipe or socket, and the writing end
 is closed, hGetBuf will behave as if EOF was reached.
hGetBuf ignores the prevailing TextEncoding and NewlineMode
 on the Handle, and reads bytes directly.
hGetBufNonBlocking :: Handle -> Ptr a -> Int -> IO Int #
hGetBufNonBlocking hdl buf count reads data from the handle hdl
 into the buffer buf until either EOF is reached, or
 count 8-bit bytes have been read, or there is no more data available
 to read immediately.
hGetBufNonBlocking is identical to hGetBuf, except that it will
 never block waiting for data to become available, instead it returns
 only whatever data is available.  To wait for data to arrive before
 calling hGetBufNonBlocking, use hWaitForInput.
If the handle is a pipe or socket, and the writing end
 is closed, hGetBufNonBlocking will behave as if EOF was reached.
hGetBufNonBlocking ignores the prevailing TextEncoding and
 NewlineMode on the Handle, and reads bytes directly.
NOTE: on Windows, this function does not work correctly; it
 behaves identically to hGetBuf.
hPutBuf :: Handle -> Ptr a -> Int -> IO () #
hPutBuf hdl buf count writes count 8-bit bytes from the
 buffer buf to the handle hdl.  It returns ().
hPutBuf ignores any text encoding that applies to the Handle,
 writing the bytes directly to the underlying file or device.
hPutBuf ignores the prevailing TextEncoding and
 NewlineMode on the Handle, and writes bytes directly.
This operation may fail with:
- ResourceVanishedif the handle is a pipe or socket, and the reading end is closed. (If this is a POSIX system, and the program has not asked to ignore SIGPIPE, then a SIGPIPE may be delivered instead, whose default action is to terminate the program).