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.

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:

• isEOFError if the end of file has been reached.

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 hdl is writable, the buffer is flushed as for hFlush;
• if hdl is not writable, the contents of the buffer is discarded.

This operation may fail with:

• isPermissionError if the handle has already been used for reading or writing and the implementation does not allow the buffering mode to be changed.

Select binary mode (True) or text mode (False) on a open handle. (See also openBinaryFile.)

This has the same effect as calling hSetEncoding with latin1, together with hSetNewlineMode with noNewlineTranslation.

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.

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:

• isFullError if the device is full;
• isPermissionError if a system resource limit would be exceeded. It is unspecified whether the characters in the buffer are discarded or retained under these circumstances.

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:

• isFullError if the device is full;
• isPermissionError if a system resource limit would be exceeded. It is unspecified whether the characters in the buffer are discarded or retained under these circumstances;
• isIllegalOperation if hdl has buffered read data, and is not seekable.

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

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:

• isPermissionError if a system resource limit would be exceeded.

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:

• isPermissionError if a system resource limit would be exceeded.

Do no newline translation at all.

 noNewlineTranslation  = NewlineMode { inputNL  = LF, outputNL = LF }

Map '\r\n' into '\n' on input, and '\n' to the native newline represetnation 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 }

Use the native newline representation on both input and output

 nativeNewlineMode  = NewlineMode { inputNL  = nativeNewline
                                    outputNL = nativeNewline }

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.

If t is less than zero, then hWaitForInput waits indefinitely.

This operation may fail with:

• isEOFError if the end of file has been reached.

NOTE for GHC users: unless you use the -threaded flag, hWaitForInput 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.

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:

• isEOFError if the end of file has been reached.

Computation hGetLine hdl reads a line from the file or channel managed by hdl.

This operation may fail with:

• isEOFError if 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.

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 hClose is 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:

• isEOFError if the end of file has been reached.

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:

• isFullError if the device is full; or
• isPermissionError if another system resource limit would be exceeded.

Computation hPutStr hdl s writes the string s to the file or channel managed by hdl.

This operation may fail with:

• isFullError if the device is full; or
• isPermissionError if another system resource limit would be exceeded.

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 ignores whatever TextEncoding the Handle is currently using, and reads bytes directly from the underlying IO device.

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 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.

hGetBufNonBlocking ignores whatever TextEncoding the Handle is currently using, and reads bytes directly from the underlying IO device.

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.

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:

• ResourceVanished if 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).