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 openBinaryFile, -- :: FilePath -> IOMode -> IO Handle
145 hSetBinaryMode, -- :: Handle -> Bool -> IO ()
146 #if !defined(__NHC__)
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 )
174 import Hugs.Prelude ( throw, Exception(NonTermination) )
175 import System.IO.Unsafe ( unsafeInterleaveIO )
182 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
183 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
184 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
185 , stdin, stdout, stderr
186 , openFile -- :: FilePath -> IOMode -> IO Handle
187 , hClose -- :: Handle -> IO ()
188 , hFileSize -- :: Handle -> IO Integer
189 , hIsEOF -- :: Handle -> IO Bool
190 , isEOF -- :: IO Bool
191 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
192 , hGetBuffering -- :: Handle -> IO BufferMode
193 , hFlush -- :: Handle -> IO ()
194 , hGetPosn -- :: Handle -> IO HandlePosn
195 , hSetPosn -- :: HandlePosn -> IO ()
196 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
197 , hWaitForInput -- :: Handle -> Int -> IO Bool
198 , hGetChar -- :: Handle -> IO Char
199 , hGetLine -- :: Handle -> IO [Char]
200 , hLookAhead -- :: Handle -> IO Char
201 , hGetContents -- :: Handle -> IO [Char]
202 , hPutChar -- :: Handle -> Char -> IO ()
203 , hPutStr -- :: Handle -> [Char] -> IO ()
204 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
205 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
206 , hIsSeekable -- :: Handle -> IO Bool
209 , FilePath -- :: String
211 import NHC.IOExtras (fixIO)
212 openBinaryFile = openFile
213 hSetBinaryMode _ _ = return ()
216 import System.IO.Error (
217 isAlreadyExistsError, isDoesNotExistError, -- :: IOError -> Bool
218 isAlreadyInUseError, isFullError,
219 isEOFError, isIllegalOperation,
220 isPermissionError, isUserError,
222 ioeGetErrorString, -- :: IOError -> String
223 ioeGetHandle, -- :: IOError -> Maybe Handle
224 ioeGetFileName, -- :: IOError -> Maybe FilePath
226 try, -- :: IO a -> IO (Either IOError a)
228 -- re-exports of Prelude names
230 ioError, -- :: IOError -> IO a
231 userError, -- :: String -> IOError
232 catch -- :: IO a -> (IOError -> IO a) -> IO a
235 -- -----------------------------------------------------------------------------
239 -- | Write a character to the standard output device
240 -- (same as 'hPutChar' 'stdout').
242 putChar :: Char -> IO ()
243 putChar c = hPutChar stdout c
245 -- | Write a string to the standard output device
246 -- (same as 'hPutStr' 'stdout').
248 putStr :: String -> IO ()
249 putStr s = hPutStr stdout s
251 -- | The same as 'putStr', but adds a newline character.
253 putStrLn :: String -> IO ()
254 putStrLn s = do putStr s
257 -- | The 'print' function outputs a value of any printable type to the
258 -- standard output device.
259 -- Printable types are those that are instances of class 'Show'; 'print'
260 -- converts values to strings for output using the 'show' operation and
263 -- For example, a program to print the first 20 integers and their
264 -- powers of 2 could be written as:
266 -- > main = print ([(n, 2^n) | n <- [0..19]])
268 print :: Show a => a -> IO ()
269 print x = putStrLn (show x)
271 -- | Read a character from the standard input device
272 -- (same as 'hGetChar' 'stdin').
275 getChar = hGetChar stdin
277 -- | Read a line from the standard input device
278 -- (same as 'hGetLine' 'stdin').
281 getLine = hGetLine stdin
283 -- | The 'getContents' operation returns all user input as a single string,
284 -- which is read lazily as it is needed
285 -- (same as 'hGetContents' 'stdin').
287 getContents :: IO String
288 getContents = hGetContents stdin
290 -- | The 'interact' function takes a function of type @String->String@
291 -- as its argument. The entire input from the standard input device is
292 -- passed to this function as its argument, and the resulting string is
293 -- output on the standard output device.
295 interact :: (String -> String) -> IO ()
296 interact f = do s <- getContents
299 -- | The 'readFile' function reads a file and
300 -- returns the contents of the file as a string.
301 -- The file is read lazily, on demand, as with 'getContents'.
303 readFile :: FilePath -> IO String
304 readFile name = openFile name ReadMode >>= hGetContents
306 -- | The computation 'writeFile' @file str@ function writes the string @str@,
307 -- to the file @file@.
309 writeFile :: FilePath -> String -> IO ()
310 writeFile name str = do
311 hdl <- openFile name WriteMode
315 -- | The computation 'appendFile' @file str@ function appends the string @str@,
316 -- to the file @file@.
318 -- Note that 'writeFile' and 'appendFile' write a literal string
319 -- to a file. To write a value of any printable type, as with 'print',
320 -- use the 'show' function to convert the value to a string first.
322 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
324 appendFile :: FilePath -> String -> IO ()
325 appendFile name str = do
326 hdl <- openFile name AppendMode
330 -- | The 'readLn' function combines 'getLine' and 'readIO'.
332 readLn :: Read a => IO a
333 readLn = do l <- getLine
337 -- | The 'readIO' function is similar to 'read' except that it signals
338 -- parse failure to the 'IO' monad instead of terminating the program.
340 readIO :: Read a => String -> IO a
341 readIO s = case (do { (x,t) <- reads s ;
345 [] -> ioError (userError "Prelude.readIO: no parse")
346 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
347 #endif /* __HUGS__ */
349 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
350 -- available for input from handle @hdl@.
352 -- This operation may fail with:
354 -- * 'isEOFError' if the end of file has been reached.
356 hReady :: Handle -> IO Bool
357 hReady h = hWaitForInput h 0
359 -- | The same as 'hPutStr', but adds a newline character.
361 hPutStrLn :: Handle -> String -> IO ()
362 hPutStrLn hndl str = do
366 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
367 -- given by the 'shows' function to the file or channel managed by @hdl@
368 -- and appends a newline.
370 -- This operation may fail with:
372 -- * 'isFullError' if the device is full; or
374 -- * 'isPermissionError' if another system resource limit would be exceeded.
376 hPrint :: Show a => Handle -> a -> IO ()
377 hPrint hdl = hPutStrLn hdl . show
379 -- ---------------------------------------------------------------------------
382 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
383 fixIO :: (a -> IO a) -> IO a
385 ref <- newIORef (throw NonTermination)
386 ans <- unsafeInterleaveIO (readIORef ref)
388 writeIORef ref result
391 -- NOTE: we do our own explicit black holing here, because GHC's lazy
392 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
393 -- computation a few times before it notices the loop, which is wrong.
397 -- Implementations should enforce as far as possible, at least locally to the
398 -- Haskell process, multiple-reader single-writer locking on files.
399 -- That is, /there may either be many handles on the same file which manage
400 -- input, or just one handle on the file which manages output/. If any
401 -- open or semi-closed handle is managing a file for output, no new
402 -- handle can be allocated for that file. If any open or semi-closed
403 -- handle is managing a file for input, new handles can only be allocated
404 -- if they do not manage output. Whether two files are the same is
405 -- implementation-dependent, but they should normally be the same if they
406 -- have the same absolute path name and neither has been renamed, for
409 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
410 -- the file until the entire contents of the file have been consumed.
411 -- It follows that an attempt to write to a file (using 'writeFile', for
412 -- example) that was earlier opened by 'readFile' will usually result in
413 -- failure with 'isAlreadyInUseError'.