/Haskell 8


Copyright (c) The University of Glasgow, 1994-2008
License see libraries/base/LICENSE
Maintainer libraries@haskell.org
Stability internal
Portability non-portable
Safe Haskell Trustworthy
Language Haskell2010


Type classes for I/O providers.

class RawIO a where Source

A low-level I/O provider where the data is bytes in memory.

Minimal complete definition

read, readNonBlocking, write, writeNonBlocking


read :: a -> Ptr Word8 -> Int -> IO Int Source

Read up to the specified number of bytes, returning the number of bytes actually read. This function should only block if there is no data available. If there is not enough data available, then the function should just return the available data. A return value of zero indicates that the end of the data stream (e.g. end of file) has been reached.

readNonBlocking :: a -> Ptr Word8 -> Int -> IO (Maybe Int) Source

Read up to the specified number of bytes, returning the number of bytes actually read, or Nothing if the end of the stream has been reached.

write :: a -> Ptr Word8 -> Int -> IO () Source

Write the specified number of bytes.

writeNonBlocking :: a -> Ptr Word8 -> Int -> IO Int Source

Write up to the specified number of bytes without blocking. Returns the actual number of bytes written.

class IODevice a where Source

I/O operations required for implementing a Handle.

Minimal complete definition

ready, close, devType


ready :: a -> Bool -> Int -> IO Bool Source

ready dev write msecs returns True if the device has data to read (if write is False) or space to write new data (if write is True). msecs specifies how long to wait, in milliseconds.

close :: a -> IO () Source

closes the device. Further operations on the device should produce exceptions.

isTerminal :: a -> IO Bool Source

returns True if the device is a terminal or console.

isSeekable :: a -> IO Bool Source

returns True if the device supports seek operations.

seek :: a -> SeekMode -> Integer -> IO () Source

seek to the specified position in the data.

tell :: a -> IO Integer Source

return the current position in the data.

getSize :: a -> IO Integer Source

return the size of the data.

setSize :: a -> Integer -> IO () Source

change the size of the data.

setEcho :: a -> Bool -> IO () Source

for terminal devices, changes whether characters are echoed on the device.

getEcho :: a -> IO Bool Source

returns the current echoing status.

setRaw :: a -> Bool -> IO () Source

some devices (e.g. terminals) support a "raw" mode where characters entered are immediately made available to the program. If available, this operations enables raw mode.

devType :: a -> IO IODeviceType Source

returns the IODeviceType corresponding to this device.

dup :: a -> IO a Source

duplicates the device, if possible. The new device is expected to share a file pointer with the original device (like Unix dup).

dup2 :: a -> a -> IO a Source

dup2 source target replaces the target device with the source device. The target device is closed first, if necessary, and then it is made into a duplicate of the first device (like Unix dup2).

data IODeviceType Source

Type of a device that can be used to back a Handle (see also mkFileHandle). The standard libraries provide creation of Handles via Posix file operations with file descriptors (see mkHandleFromFD) with FD being the underlying IODevice instance.

Users may provide custom instances of IODevice which are expected to conform the following rules:



The standard libraries do not have direct support for this device type, but a user implementation is expected to provide a list of file names in the directory, in any order, separated by '\0' characters, excluding the "." and ".." names. See also getDirectoryContents. Seek operations are not supported on directories (other than to the zero position).


A duplex communications channel (results in creation of a duplex Handle). The standard libraries use this device type when creating Handles for open sockets.


A file that may be read or written, and also may be seekable.


A "raw" (disk) device which supports block binary read and write operations and may be seekable only to positions of certain granularity (block- aligned).

data SeekMode Source

A mode that determines the effect of hSeek hdl mode i.



the position of hdl is set to i.


the position of hdl is set to offset i from the current position.


the position of hdl is set to offset i from the end of the file.


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Licensed under a BSD-style license (see top of the page).