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 , hPutStrLn -- :: Handle -> [Char] -> IO ()
205 , hPrint -- :: Handle -> [Char] -> IO ()
206 , hReady -- :: Handle -> [Char] -> IO ()
207 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
208 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
209 , hIsSeekable -- :: Handle -> IO Bool
212 , FilePath -- :: String
214 import NHC.IOExtras (fixIO)
217 import System.IO.Error (
218 isAlreadyExistsError, isDoesNotExistError, -- :: IOError -> Bool
219 isAlreadyInUseError, isFullError,
220 isEOFError, isIllegalOperation,
221 isPermissionError, isUserError,
223 ioeGetErrorString, -- :: IOError -> String
224 ioeGetHandle, -- :: IOError -> Maybe Handle
225 ioeGetFileName, -- :: IOError -> Maybe FilePath
227 try, -- :: IO a -> IO (Either IOError a)
229 -- re-exports of Prelude names
231 ioError, -- :: IOError -> IO a
232 userError, -- :: String -> IOError
233 catch -- :: IO a -> (IOError -> IO a) -> IO a
236 -- -----------------------------------------------------------------------------
239 #ifdef __GLASGOW_HASKELL__
240 -- | Write a character to the standard output device
241 -- (same as 'hPutChar' 'stdout').
243 putChar :: Char -> IO ()
244 putChar c = hPutChar stdout c
246 -- | Write a string to the standard output device
247 -- (same as 'hPutStr' 'stdout').
249 putStr :: String -> IO ()
250 putStr s = hPutStr stdout s
252 -- | The same as 'putStr', but adds a newline character.
254 putStrLn :: String -> IO ()
255 putStrLn s = do putStr s
258 -- | The 'print' function outputs a value of any printable type to the
259 -- standard output device.
260 -- Printable types are those that are instances of class 'Show'; 'print'
261 -- converts values to strings for output using the 'show' operation and
264 -- For example, a program to print the first 20 integers and their
265 -- powers of 2 could be written as:
267 -- > main = print ([(n, 2^n) | n <- [0..19]])
269 print :: Show a => a -> IO ()
270 print x = putStrLn (show x)
272 -- | Read a character from the standard input device
273 -- (same as 'hGetChar' 'stdin').
276 getChar = hGetChar stdin
278 -- | Read a line from the standard input device
279 -- (same as 'hGetLine' 'stdin').
282 getLine = hGetLine stdin
284 -- | The 'getContents' operation returns all user input as a single string,
285 -- which is read lazily as it is needed
286 -- (same as 'hGetContents' 'stdin').
288 getContents :: IO String
289 getContents = hGetContents stdin
291 -- | The 'interact' function takes a function of type @String->String@
292 -- as its argument. The entire input from the standard input device is
293 -- passed to this function as its argument, and the resulting string is
294 -- output on the standard output device.
296 interact :: (String -> String) -> IO ()
297 interact f = do s <- getContents
300 -- | The 'readFile' function reads a file and
301 -- returns the contents of the file as a string.
302 -- The file is read lazily, on demand, as with 'getContents'.
304 readFile :: FilePath -> IO String
305 readFile name = openFile name ReadMode >>= hGetContents
307 -- | The computation 'writeFile' @file str@ function writes the string @str@,
308 -- to the file @file@.
310 writeFile :: FilePath -> String -> IO ()
311 writeFile name str = do
312 hdl <- openFile name WriteMode
316 -- | The computation 'appendFile' @file str@ function appends the string @str@,
317 -- to the file @file@.
319 -- Note that 'writeFile' and 'appendFile' write a literal string
320 -- to a file. To write a value of any printable type, as with 'print',
321 -- use the 'show' function to convert the value to a string first.
323 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
325 appendFile :: FilePath -> String -> IO ()
326 appendFile name str = do
327 hdl <- openFile name AppendMode
331 -- | The 'readLn' function combines 'getLine' and 'readIO'.
333 readLn :: Read a => IO a
334 readLn = do l <- getLine
338 -- | The 'readIO' function is similar to 'read' except that it signals
339 -- parse failure to the 'IO' monad instead of terminating the program.
341 readIO :: Read a => String -> IO a
342 readIO s = case (do { (x,t) <- reads s ;
346 [] -> ioError (userError "Prelude.readIO: no parse")
347 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
348 #endif /* __GLASGOW_HASKELL__ */
351 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
352 -- available for input from handle @hdl@.
354 -- This operation may fail with:
356 -- * 'isEOFError' if the end of file has been reached.
358 hReady :: Handle -> IO Bool
359 hReady h = hWaitForInput h 0
361 -- | The same as 'hPutStr', but adds a newline character.
363 hPutStrLn :: Handle -> String -> IO ()
364 hPutStrLn hndl str = do
368 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
369 -- given by the 'shows' function to the file or channel managed by @hdl@
370 -- and appends a newline.
372 -- This operation may fail with:
374 -- * 'isFullError' if the device is full; or
376 -- * 'isPermissionError' if another system resource limit would be exceeded.
378 hPrint :: Show a => Handle -> a -> IO ()
379 hPrint hdl = hPutStrLn hdl . show
380 #endif /* !__NHC__ */
382 -- ---------------------------------------------------------------------------
385 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
386 fixIO :: (a -> IO a) -> IO a
388 ref <- newIORef (throw NonTermination)
389 ans <- unsafeInterleaveIO (readIORef ref)
391 writeIORef ref result
394 -- NOTE: we do our own explicit black holing here, because GHC's lazy
395 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
396 -- computation a few times before it notices the loop, which is wrong.
400 -- Assume a unix platform, where text and binary I/O are identical.
401 openBinaryFile = openFile
402 hSetBinaryMode _ _ = return ()
406 -- Implementations should enforce as far as possible, at least locally to the
407 -- Haskell process, multiple-reader single-writer locking on files.
408 -- That is, /there may either be many handles on the same file which manage
409 -- input, or just one handle on the file which manages output/. If any
410 -- open or semi-closed handle is managing a file for output, no new
411 -- handle can be allocated for that file. If any open or semi-closed
412 -- handle is managing a file for input, new handles can only be allocated
413 -- if they do not manage output. Whether two files are the same is
414 -- implementation-dependent, but they should normally be the same if they
415 -- have the same absolute path name and neither has been renamed, for
418 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
419 -- the file until the entire contents of the file have been consumed.
420 -- It follows that an attempt to write to a file (using 'writeFile', for
421 -- example) that was earlier opened by 'readFile' will usually result in
422 -- failure with 'isAlreadyInUseError'.