| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell98 |
System.Path.IO
Description
This module provides type-safe access to IO operations.
It is designed to be imported instead of System.IO. (It is intended to provide versions of functions from that module which have equivalent functionality but are more typesafe). System.Path is a companion module providing a type-safe alternative to System.FilePath.
You will typically want to import as follows:
import Prelude hiding (FilePath) import qualified System.Path as Path import qualified System.Path.Directory as Dir import qualified System.Path.IO as PIO
Ben Moseley - (c) 2009
Synopsis
- withFile :: AbsRel ar => FilePath ar -> IOMode -> (Handle -> IO r) -> IO r
- openFile :: AbsRel ar => FilePath ar -> IOMode -> IO Handle
- readFile :: AbsRel ar => FilePath ar -> IO String
- writeFile :: AbsRel ar => FilePath ar -> String -> IO ()
- appendFile :: AbsRel ar => FilePath ar -> String -> IO ()
- withBinaryFile :: AbsRel ar => FilePath ar -> IOMode -> (Handle -> IO r) -> IO r
- openBinaryFile :: AbsRel ar => FilePath ar -> IOMode -> IO Handle
- openTempFile :: AbsRel ar => DirPath ar -> RelFile -> IO (AbsFile, Handle)
- openBinaryTempFile :: AbsRel ar => DirPath ar -> RelFile -> IO (AbsFile, Handle)
- data IO a
- fixIO :: (a -> IO a) -> IO a
- data Handle
- stdin :: Handle
- stdout :: Handle
- stderr :: Handle
- data IOMode
- hClose :: Handle -> IO ()
- hFileSize :: Handle -> IO Integer
- hSetFileSize :: Handle -> Integer -> IO ()
- hIsEOF :: Handle -> IO Bool
- isEOF :: IO Bool
- data BufferMode
- hSetBuffering :: Handle -> BufferMode -> IO ()
- hGetBuffering :: Handle -> IO BufferMode
- hFlush :: Handle -> IO ()
- hGetPosn :: Handle -> IO HandlePosn
- hSetPosn :: HandlePosn -> IO ()
- data HandlePosn
- hSeek :: Handle -> SeekMode -> Integer -> IO ()
- data SeekMode
- hTell :: Handle -> IO Integer
- hIsOpen :: Handle -> IO Bool
- hIsClosed :: Handle -> IO Bool
- hIsReadable :: Handle -> IO Bool
- hIsWritable :: Handle -> IO Bool
- hIsSeekable :: Handle -> IO Bool
- hIsTerminalDevice :: Handle -> IO Bool
- hSetEcho :: Handle -> Bool -> IO ()
- hGetEcho :: Handle -> IO Bool
- hShow :: Handle -> IO String
- hWaitForInput :: Handle -> Int -> IO Bool
- hReady :: Handle -> IO Bool
- hGetChar :: Handle -> IO Char
- hGetLine :: Handle -> IO String
- hLookAhead :: Handle -> IO Char
- hGetContents :: Handle -> IO String
- hPutChar :: Handle -> Char -> IO ()
- hPutStr :: Handle -> String -> IO ()
- hPutStrLn :: Handle -> String -> IO ()
- hPrint :: Show a => Handle -> a -> IO ()
- interact :: (String -> String) -> IO ()
- putChar :: Char -> IO ()
- putStr :: String -> IO ()
- putStrLn :: String -> IO ()
- print :: Show a => a -> IO ()
- getChar :: IO Char
- getLine :: IO String
- getContents :: IO String
- readIO :: Read a => String -> IO a
- readLn :: Read a => IO a
- hSetBinaryMode :: Handle -> Bool -> IO ()
- hPutBuf :: Handle -> Ptr a -> Int -> IO ()
- hGetBuf :: Handle -> Ptr a -> Int -> IO Int
- hPutBufNonBlocking :: Handle -> Ptr a -> Int -> IO Int
- hGetBufNonBlocking :: Handle -> Ptr a -> Int -> IO Int
Covers for System.IO functions
Re-exports
A value of type IO aa.
There is really only one way to "perform" an I/O action: bind it to
Main.main in your program. When your program is run, the I/O will
be performed. It isn't possible to perform I/O from an arbitrary
function, unless that function is itself in the IO monad and called
at some point, directly or indirectly, from Main.main.
IO is a monad, so IO actions can be combined using either the do-notation
or the >> and >>= operations from the Monad
class.
Instances
fixIO :: (a -> IO a) -> IO a #
The implementation of mfix for IO. If the function
passed to fixIO inspects its argument, the resulting action will throw
FixIOException.
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.
Instances
See openFile
Constructors
| ReadMode | |
| WriteMode | |
| AppendMode | |
| ReadWriteMode |
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 is an interruptible operation in the sense described in
Control.Exception. If hClose is interrupted by an asynchronous
exception in the process of flushing its buffers, then the I/O device
(e.g., file) will be closed anyway.
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.
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
| Read BufferMode | Since: base-4.2.0.0 |
Defined in GHC.IO.Handle.Types Methods readsPrec :: Int -> ReadS BufferMode # readList :: ReadS [BufferMode] # readPrec :: ReadPrec BufferMode # readListPrec :: ReadPrec [BufferMode] # | |
| Show BufferMode | Since: base-4.2.0.0 |
Defined in GHC.IO.Handle.Types Methods showsPrec :: Int -> BufferMode -> ShowS # show :: BufferMode -> String # showList :: [BufferMode] -> ShowS # | |
| Eq BufferMode | Since: base-4.2.0.0 |
Defined in GHC.IO.Handle.Types | |
| Ord BufferMode | Since: base-4.2.0.0 |
Defined in GHC.IO.Handle.Types Methods compare :: BufferMode -> BufferMode -> Ordering # (<) :: BufferMode -> BufferMode -> Bool # (<=) :: BufferMode -> BufferMode -> Bool # (>) :: BufferMode -> BufferMode -> Bool # (>=) :: BufferMode -> BufferMode -> Bool # max :: BufferMode -> BufferMode -> BufferMode # min :: BufferMode -> BufferMode -> BufferMode # | |
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.
hGetBuffering :: Handle -> IO BufferMode #
Computation hGetBuffering hdl returns the current buffering mode
for hdl.
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.
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.
data HandlePosn #
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 | |
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.
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 | |
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 #
hIsSeekable :: Handle -> IO Bool #
hIsTerminalDevice :: Handle -> IO Bool #
Is the handle connected to a terminal?
On Windows the result of hIsTerminalDevide might be misleading,
because non-native terminals, such as MinTTY used in MSYS and Cygwin environments,
are implemented via redirection.
Use System.Win32.Types.withHandleToHANDLE System.Win32.MinTTY.isMinTTYHandle
to recognise it. Also consider ansi-terminal package for crossplatform terminal
support.
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.
Computation hReady hdl indicates whether at least one item is
available for input from handle hdl.
This operation may fail with:
isEOFErrorif the end of file has been reached.
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.
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.
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.
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; orisPermissionErrorif 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; orisPermissionErrorif another system resource limit would be exceeded.
hPrint :: Show a => Handle -> a -> IO () #
Computation hPrint hdl t writes the string representation of t
given by the shows function to the file or channel managed by hdl
and appends a newline.
This operation may fail with:
isFullErrorif the device is full; orisPermissionErrorif another system resource limit would be exceeded.
interact :: (String -> String) -> IO () #
The interact function takes a function of type String->String
as its argument. The entire input from the standard input device is
passed to this function as its argument, and the resulting string is
output on the standard output device.
print :: Show a => a -> IO () #
The print function outputs a value of any printable type to the
standard output device.
Printable types are those that are instances of class Show; print
converts values to strings for output using the show operation and
adds a newline.
For example, a program to print the first 20 integers and their powers of 2 could be written as:
main = print ([(n, 2^n) | n <- [0..19]])
getContents :: IO String #
The getContents operation returns all user input as a single string,
which is read lazily as it is needed
(same as hGetContents stdin).
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.
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).
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.