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
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
146 hSetBinaryMode, -- :: Handle -> Bool -> IO ()
147 hPutBuf, -- :: Handle -> Ptr a -> Int -> IO ()
148 hGetBuf, -- :: Handle -> Ptr a -> Int -> IO Int
150 #if !defined(__NHC__) && !defined(__HUGS__)
151 hPutBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
152 hGetBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
155 module System.IO.Error,
158 #ifdef __GLASGOW_HASKELL__
160 import GHC.IOBase -- Together these four Prelude modules define
161 import GHC.Handle -- all the stuff exported by IO for the GHC version
163 import GHC.ST ( fixST )
179 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
180 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
181 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
182 , stdin, stdout, stderr
183 , openFile -- :: FilePath -> IOMode -> IO Handle
184 , hClose -- :: Handle -> IO ()
185 , hFileSize -- :: Handle -> IO Integer
186 , hIsEOF -- :: Handle -> IO Bool
187 , isEOF -- :: IO Bool
188 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
189 , hGetBuffering -- :: Handle -> IO BufferMode
190 , hFlush -- :: Handle -> IO ()
191 , hGetPosn -- :: Handle -> IO HandlePosn
192 , hSetPosn -- :: HandlePosn -> IO ()
193 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
194 , hWaitForInput -- :: Handle -> Int -> IO Bool
195 , hGetChar -- :: Handle -> IO Char
196 , hGetLine -- :: Handle -> IO [Char]
197 , hLookAhead -- :: Handle -> IO Char
198 , hGetContents -- :: Handle -> IO [Char]
199 , hPutChar -- :: Handle -> Char -> IO ()
200 , hPutStr -- :: Handle -> [Char] -> IO ()
201 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
202 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
203 , hIsSeekable -- :: Handle -> IO Bool
206 , FilePath -- :: String
208 import NHC.IOExtras (fixIO)
211 import System.IO.Error (
212 isAlreadyExistsError, isDoesNotExistError, -- :: IOError -> Bool
213 isAlreadyInUseError, isFullError,
214 isEOFError, isIllegalOperation,
215 isPermissionError, isUserError,
217 ioeGetErrorString, -- :: IOError -> String
218 ioeGetHandle, -- :: IOError -> Maybe Handle
219 ioeGetFileName, -- :: IOError -> Maybe FilePath
221 try, -- :: IO a -> IO (Either IOError a)
223 -- re-exports of Prelude names
225 ioError, -- :: IOError -> IO a
226 userError, -- :: String -> IOError
227 catch -- :: IO a -> (IOError -> IO a) -> IO a
230 -- -----------------------------------------------------------------------------
234 -- | Write a character to the standard output device
235 -- (same as 'hPutChar' 'stdout').
237 putChar :: Char -> IO ()
238 putChar c = hPutChar stdout c
240 -- | Write a string to the standard output device
241 -- (same as 'hPutStr' 'stdout').
243 putStr :: String -> IO ()
244 putStr s = hPutStr stdout s
246 -- | The same as 'putStr', but adds a newline character.
248 putStrLn :: String -> IO ()
249 putStrLn s = do putStr s
252 -- | The 'print' function outputs a value of any printable type to the
253 -- standard output device.
254 -- Printable types are those that are instances of class 'Show'; 'print'
255 -- converts values to strings for output using the 'show' operation and
258 -- For example, a program to print the first 20 integers and their
259 -- powers of 2 could be written as:
261 -- > main = print ([(n, 2^n) | n <- [0..19]])
263 print :: Show a => a -> IO ()
264 print x = putStrLn (show x)
266 -- | Read a character from the standard input device
267 -- (same as 'hGetChar' 'stdin').
270 getChar = hGetChar stdin
272 -- | Read a line from the standard input device
273 -- (same as 'hGetLine' 'stdin').
276 getLine = hGetLine stdin
278 -- | The 'getContents' operation returns all user input as a single string,
279 -- which is read lazily as it is needed
280 -- (same as 'hGetContents' 'stdin').
282 getContents :: IO String
283 getContents = hGetContents stdin
285 -- | The 'interact' function takes a function of type @String->String@
286 -- as its argument. The entire input from the standard input device is
287 -- passed to this function as its argument, and the resulting string is
288 -- output on the standard output device.
290 interact :: (String -> String) -> IO ()
291 interact f = do s <- getContents
294 -- | The 'readFile' function reads a file and
295 -- returns the contents of the file as a string.
296 -- The file is read lazily, on demand, as with 'getContents'.
298 readFile :: FilePath -> IO String
299 readFile name = openFile name ReadMode >>= hGetContents
301 -- | The computation 'writeFile' @file str@ function writes the string @str@,
302 -- to the file @file@.
304 writeFile :: FilePath -> String -> IO ()
305 writeFile name str = do
306 hdl <- openFile name WriteMode
310 -- | The computation 'appendFile' @file str@ function appends the string @str@,
311 -- to the file @file@.
313 -- Note that 'writeFile' and 'appendFile' write a literal string
314 -- to a file. To write a value of any printable type, as with 'print',
315 -- use the 'show' function to convert the value to a string first.
317 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
319 appendFile :: FilePath -> String -> IO ()
320 appendFile name str = do
321 hdl <- openFile name AppendMode
325 -- | The 'readLn' function combines 'getLine' and 'readIO'.
327 readLn :: Read a => IO a
328 readLn = do l <- getLine
332 -- | The 'readIO' function is similar to 'read' except that it signals
333 -- parse failure to the 'IO' monad instead of terminating the program.
335 readIO :: Read a => String -> IO a
336 readIO s = case (do { (x,t) <- reads s ;
340 [] -> ioError (userError "Prelude.readIO: no parse")
341 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
342 #endif /* __HUGS__ */
344 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
345 -- available for input from handle @hdl@.
347 -- This operation may fail with:
349 -- * 'isEOFError' if the end of file has been reached.
351 hReady :: Handle -> IO Bool
352 hReady h = hWaitForInput h 0
354 -- | The same as 'hPutStr', but adds a newline character.
356 hPutStrLn :: Handle -> String -> IO ()
357 hPutStrLn hndl str = do
361 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
362 -- given by the 'shows' function to the file or channel managed by @hdl@
363 -- and appends a newline.
365 -- This operation may fail with:
367 -- * 'isFullError' if the device is full; or
369 -- * 'isPermissionError' if another system resource limit would be exceeded.
371 hPrint :: Show a => Handle -> a -> IO ()
372 hPrint hdl = hPutStrLn hdl . show
374 -- ---------------------------------------------------------------------------
377 #ifdef __GLASGOW_HASKELL__
378 fixIO :: (a -> IO a) -> IO a
379 fixIO m = stToIO (fixST (ioToST . m))
383 -- Implementations should enforce as far as possible, at least locally to the
384 -- Haskell process, multiple-reader single-writer locking on files.
385 -- That is, /there may either be many handles on the same file which manage
386 -- input, or just one handle on the file which manages output/. If any
387 -- open or semi-closed handle is managing a file for output, no new
388 -- handle can be allocated for that file. If any open or semi-closed
389 -- handle is managing a file for input, new handles can only be allocated
390 -- if they do not manage output. Whether two files are the same is
391 -- implementation-dependent, but they should normally be the same if they
392 -- have the same absolute path name and neither has been renamed, for
395 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
396 -- the file until the entire contents of the file have been consumed.
397 -- It follows that an attempt to write to a file (using 'writeFile', for
398 -- example) that was earlier opened by 'readFile' will usually result in
399 -- failure with 'isAlreadyInUseError'.