1 {-# OPTIONS -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
5 -- Copyright : (c) The University of Glasgow 2001
6 -- License : BSD-style (see the file libraries/base/LICENSE)
8 -- Maintainer : libraries@haskell.org
10 -- Portability : portable
12 -- The standard IO library.
14 -----------------------------------------------------------------------------
19 IO, -- instance MonadFix
20 fixIO, -- :: (a -> IO a) -> IO a
22 -- * Files and handles
24 FilePath, -- :: String
26 Handle, -- abstract, instance of: Eq, Show.
28 -- ** Standard handles
30 -- | Three handles are allocated during program initialisation,
31 -- and are initially open.
33 stdin, stdout, stderr, -- :: Handle
35 -- * Opening and closing files
39 openFile, -- :: FilePath -> IOMode -> IO Handle
40 IOMode(ReadMode,WriteMode,AppendMode,ReadWriteMode),
44 hClose, -- :: Handle -> IO ()
48 -- | These functions are also exported by the "Prelude".
50 readFile, -- :: FilePath -> IO String
51 writeFile, -- :: FilePath -> String -> IO ()
52 appendFile, -- :: FilePath -> String -> IO ()
58 -- * Operations on handles
60 -- ** Determining the size of a file
62 hFileSize, -- :: Handle -> IO Integer
64 -- ** Detecting the end of input
66 hIsEOF, -- :: Handle -> IO Bool
69 -- ** Buffering operations
71 BufferMode(NoBuffering,LineBuffering,BlockBuffering),
72 hSetBuffering, -- :: Handle -> BufferMode -> IO ()
73 hGetBuffering, -- :: Handle -> IO BufferMode
74 hFlush, -- :: Handle -> IO ()
76 -- ** Repositioning handles
78 hGetPosn, -- :: Handle -> IO HandlePosn
79 hSetPosn, -- :: HandlePosn -> IO ()
80 HandlePosn, -- abstract, instance of: Eq, Show.
82 hSeek, -- :: Handle -> SeekMode -> Integer -> IO ()
83 SeekMode(AbsoluteSeek,RelativeSeek,SeekFromEnd),
85 hTell, -- :: Handle -> IO Integer
88 -- ** Handle properties
90 hIsOpen, hIsClosed, -- :: Handle -> IO Bool
91 hIsReadable, hIsWritable, -- :: Handle -> IO Bool
92 hIsSeekable, -- :: Handle -> IO Bool
94 -- ** Terminal operations
96 #if !defined(__HUGS__) && !defined(__NHC__)
97 hIsTerminalDevice, -- :: Handle -> IO Bool
99 hSetEcho, -- :: Handle -> Bool -> IO ()
100 hGetEcho, -- :: Handle -> IO Bool
103 -- ** Showing handle state
105 #ifdef __GLASGOW_HASKELL__
106 hShow, -- :: Handle -> IO String
109 -- * Text input and output
113 hWaitForInput, -- :: Handle -> Int -> IO Bool
114 hReady, -- :: Handle -> IO Bool
115 hGetChar, -- :: Handle -> IO Char
116 hGetLine, -- :: Handle -> IO [Char]
117 hLookAhead, -- :: Handle -> IO Char
118 hGetContents, -- :: Handle -> IO [Char]
122 hPutChar, -- :: Handle -> Char -> IO ()
123 hPutStr, -- :: Handle -> [Char] -> IO ()
124 hPutStrLn, -- :: Handle -> [Char] -> IO ()
125 hPrint, -- :: Show a => Handle -> a -> IO ()
127 -- ** Special cases for standard input and output
129 -- | These functions are also exported by the "Prelude".
131 interact, -- :: (String -> String) -> IO ()
132 putChar, -- :: Char -> IO ()
133 putStr, -- :: String -> IO ()
134 putStrLn, -- :: String -> IO ()
135 print, -- :: Show a => a -> IO ()
136 getChar, -- :: IO Char
137 getLine, -- :: IO String
138 getContents, -- :: IO String
139 readIO, -- :: Read a => String -> IO a
140 readLn, -- :: Read a => IO a
142 -- * Binary input and output
144 #if !defined(__NHC__)
145 openBinaryFile, -- :: FilePath -> IOMode -> IO Handle
148 #if !defined(__HUGS__) && !defined(__NHC__)
149 hSetBinaryMode, -- :: Handle -> Bool -> IO ()
150 hPutBuf, -- :: Handle -> Ptr a -> Int -> IO ()
151 hGetBuf, -- :: Handle -> Ptr a -> Int -> IO Int
152 hPutBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
153 hGetBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
156 module System.IO.Error,
159 #ifdef __GLASGOW_HASKELL__
161 import GHC.IOBase -- Together these four Prelude modules define
162 import GHC.Handle -- all the stuff exported by IO for the GHC version
164 import GHC.ST ( fixST )
180 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
181 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
182 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
183 , stdin, stdout, stderr
184 , openFile -- :: FilePath -> IOMode -> IO Handle
185 , hClose -- :: Handle -> IO ()
186 , hFileSize -- :: Handle -> IO Integer
187 , hIsEOF -- :: Handle -> IO Bool
188 , isEOF -- :: IO Bool
189 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
190 , hGetBuffering -- :: Handle -> IO BufferMode
191 , hFlush -- :: Handle -> IO ()
192 , hGetPosn -- :: Handle -> IO HandlePosn
193 , hSetPosn -- :: HandlePosn -> IO ()
194 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
195 , hWaitForInput -- :: Handle -> Int -> IO Bool
196 , hGetChar -- :: Handle -> IO Char
197 , hGetLine -- :: Handle -> IO [Char]
198 , hLookAhead -- :: Handle -> IO Char
199 , hGetContents -- :: Handle -> IO [Char]
200 , hPutChar -- :: Handle -> Char -> IO ()
201 , hPutStr -- :: Handle -> [Char] -> IO ()
202 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
203 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
204 , hIsSeekable -- :: Handle -> IO Bool
207 , FilePath -- :: String
209 import NHC.IOExtras (fixIO)
212 import System.IO.Error (
213 isAlreadyExistsError, isDoesNotExistError, -- :: IOError -> Bool
214 isAlreadyInUseError, isFullError,
215 isEOFError, isIllegalOperation,
216 isPermissionError, isUserError,
218 ioeGetErrorString, -- :: IOError -> String
219 ioeGetHandle, -- :: IOError -> Maybe Handle
220 ioeGetFileName, -- :: IOError -> Maybe FilePath
222 try, -- :: IO a -> IO (Either IOError a)
224 -- re-exports of Prelude names
226 ioError, -- :: IOError -> IO a
227 userError, -- :: String -> IOError
228 catch -- :: IO a -> (IOError -> IO a) -> IO a
231 -- -----------------------------------------------------------------------------
235 -- | Write a character to the standard output device
236 -- (same as 'hPutChar' 'stdout').
238 putChar :: Char -> IO ()
239 putChar c = hPutChar stdout c
241 -- | Write a string to the standard output device
242 -- (same as 'hPutStr' 'stdout').
244 putStr :: String -> IO ()
245 putStr s = hPutStr stdout s
247 -- | The same as 'putStr', but adds a newline character.
249 putStrLn :: String -> IO ()
250 putStrLn s = do putStr s
253 -- | The 'print' function outputs a value of any printable type to the
254 -- standard output device.
255 -- Printable types are those that are instances of class 'Show'; 'print'
256 -- converts values to strings for output using the 'show' operation and
259 -- For example, a program to print the first 20 integers and their
260 -- powers of 2 could be written as:
262 -- > main = print ([(n, 2^n) | n <- [0..19]])
264 print :: Show a => a -> IO ()
265 print x = putStrLn (show x)
267 -- | Read a character from the standard input device
268 -- (same as 'hGetChar' 'stdin').
271 getChar = hGetChar stdin
273 -- | Read a line from the standard input device
274 -- (same as 'hGetLine' 'stdin').
277 getLine = hGetLine stdin
279 -- | The 'getContents' operation returns all user input as a single string,
280 -- which is read lazily as it is needed
281 -- (same as 'hGetContents' 'stdin').
283 getContents :: IO String
284 getContents = hGetContents stdin
286 -- | The 'interact' function takes a function of type @String->String@
287 -- as its argument. The entire input from the standard input device is
288 -- passed to this function as its argument, and the resulting string is
289 -- output on the standard output device.
291 interact :: (String -> String) -> IO ()
292 interact f = do s <- getContents
295 -- | The 'readFile' function reads a file and
296 -- returns the contents of the file as a string.
297 -- The file is read lazily, on demand, as with 'getContents'.
299 readFile :: FilePath -> IO String
300 readFile name = openFile name ReadMode >>= hGetContents
302 -- | The computation 'writeFile' @file str@ function writes the string @str@,
303 -- to the file @file@.
305 writeFile :: FilePath -> String -> IO ()
306 writeFile name str = do
307 hdl <- openFile name WriteMode
311 -- | The computation 'appendFile' @file str@ function appends the string @str@,
312 -- to the file @file@.
314 -- Note that 'writeFile' and 'appendFile' write a literal string
315 -- to a file. To write a value of any printable type, as with 'print',
316 -- use the 'show' function to convert the value to a string first.
318 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
320 appendFile :: FilePath -> String -> IO ()
321 appendFile name str = do
322 hdl <- openFile name AppendMode
326 -- | The 'readLn' function combines 'getLine' and 'readIO'.
328 readLn :: Read a => IO a
329 readLn = do l <- getLine
333 -- | The 'readIO' function is similar to 'read' except that it signals
334 -- parse failure to the 'IO' monad instead of terminating the program.
336 readIO :: Read a => String -> IO a
337 readIO s = case (do { (x,t) <- reads s ;
341 [] -> ioError (userError "Prelude.readIO: no parse")
342 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
343 #endif /* __HUGS__ */
345 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
346 -- available for input from handle @hdl@.
348 -- This operation may fail with:
350 -- * 'isEOFError' if the end of file has been reached.
352 hReady :: Handle -> IO Bool
353 hReady h = hWaitForInput h 0
355 -- | The same as 'hPutStr', but adds a newline character.
357 hPutStrLn :: Handle -> String -> IO ()
358 hPutStrLn hndl str = do
362 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
363 -- given by the 'shows' function to the file or channel managed by @hdl@
364 -- and appends a newline.
366 -- This operation may fail with:
368 -- * 'isFullError' if the device is full; or
370 -- * 'isPermissionError' if another system resource limit would be exceeded.
372 hPrint :: Show a => Handle -> a -> IO ()
373 hPrint hdl = hPutStrLn hdl . show
375 -- ---------------------------------------------------------------------------
378 #ifdef __GLASGOW_HASKELL__
379 fixIO :: (a -> IO a) -> IO a
380 fixIO m = stToIO (fixST (ioToST . m))
384 -- Implementations should enforce as far as possible, at least locally to the
385 -- Haskell process, multiple-reader single-writer locking on files.
386 -- That is, /there may either be many handles on the same file which manage
387 -- input, or just one handle on the file which manages output/. If any
388 -- open or semi-closed handle is managing a file for output, no new
389 -- handle can be allocated for that file. If any open or semi-closed
390 -- handle is managing a file for input, new handles can only be allocated
391 -- if they do not manage output. Whether two files are the same is
392 -- implementation-dependent, but they should normally be the same if they
393 -- have the same absolute path name and neither has been renamed, for
396 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
397 -- the file until the entire contents of the file have been consumed.
398 -- It follows that an attempt to write to a file (using 'writeFile', for
399 -- example) that was earlier opened by 'readFile' will usually result in
400 -- failure with 'isAlreadyInUseError'.