1 {-# OPTIONS_GHC -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
40 openFile, -- :: FilePath -> IOMode -> IO Handle
41 IOMode(ReadMode,WriteMode,AppendMode,ReadWriteMode),
45 hClose, -- :: Handle -> IO ()
49 -- | These functions are also exported by the "Prelude".
51 readFile, -- :: FilePath -> IO String
52 writeFile, -- :: FilePath -> String -> IO ()
53 appendFile, -- :: FilePath -> String -> IO ()
59 -- * Operations on handles
61 -- ** Determining and changing the size of a file
63 hFileSize, -- :: Handle -> IO Integer
64 #ifdef __GLASGOW_HASKELL__
65 hSetFileSize, -- :: Handle -> Integer -> IO ()
68 -- ** Detecting the end of input
70 hIsEOF, -- :: Handle -> IO Bool
73 -- ** Buffering operations
75 BufferMode(NoBuffering,LineBuffering,BlockBuffering),
76 hSetBuffering, -- :: Handle -> BufferMode -> IO ()
77 hGetBuffering, -- :: Handle -> IO BufferMode
78 hFlush, -- :: Handle -> IO ()
80 -- ** Repositioning handles
82 hGetPosn, -- :: Handle -> IO HandlePosn
83 hSetPosn, -- :: HandlePosn -> IO ()
84 HandlePosn, -- abstract, instance of: Eq, Show.
86 hSeek, -- :: Handle -> SeekMode -> Integer -> IO ()
87 SeekMode(AbsoluteSeek,RelativeSeek,SeekFromEnd),
89 hTell, -- :: Handle -> IO Integer
92 -- ** Handle properties
94 hIsOpen, hIsClosed, -- :: Handle -> IO Bool
95 hIsReadable, hIsWritable, -- :: Handle -> IO Bool
96 hIsSeekable, -- :: Handle -> IO Bool
98 -- ** Terminal operations
100 #if !defined(__NHC__)
101 hIsTerminalDevice, -- :: Handle -> IO Bool
103 hSetEcho, -- :: Handle -> Bool -> IO ()
104 hGetEcho, -- :: Handle -> IO Bool
107 -- ** Showing handle state
109 #ifdef __GLASGOW_HASKELL__
110 hShow, -- :: Handle -> IO String
113 -- * Text input and output
117 hWaitForInput, -- :: Handle -> Int -> IO Bool
118 hReady, -- :: Handle -> IO Bool
119 hGetChar, -- :: Handle -> IO Char
120 hGetLine, -- :: Handle -> IO [Char]
121 hLookAhead, -- :: Handle -> IO Char
122 hGetContents, -- :: Handle -> IO [Char]
126 hPutChar, -- :: Handle -> Char -> IO ()
127 hPutStr, -- :: Handle -> [Char] -> IO ()
128 hPutStrLn, -- :: Handle -> [Char] -> IO ()
129 hPrint, -- :: Show a => Handle -> a -> IO ()
131 -- ** Special cases for standard input and output
133 -- | These functions are also exported by the "Prelude".
135 interact, -- :: (String -> String) -> IO ()
136 putChar, -- :: Char -> IO ()
137 putStr, -- :: String -> IO ()
138 putStrLn, -- :: String -> IO ()
139 print, -- :: Show a => a -> IO ()
140 getChar, -- :: IO Char
141 getLine, -- :: IO String
142 getContents, -- :: IO String
143 readIO, -- :: Read a => String -> IO a
144 readLn, -- :: Read a => IO a
146 -- * Binary input and output
149 openBinaryFile, -- :: FilePath -> IOMode -> IO Handle
150 hSetBinaryMode, -- :: Handle -> Bool -> IO ()
151 hPutBuf, -- :: Handle -> Ptr a -> Int -> IO ()
152 hGetBuf, -- :: Handle -> Ptr a -> Int -> IO Int
153 #if !defined(__NHC__) && !defined(__HUGS__)
154 hPutBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
155 hGetBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
167 import Foreign.C.Error
168 import Foreign.C.String
169 import System.Posix.Internals
171 #ifdef __GLASGOW_HASKELL__
172 import GHC.Exception as ExceptionBase hiding (catch)
175 import Hugs.Exception as ExceptionBase
178 #ifdef __GLASGOW_HASKELL__
180 import GHC.IOBase -- Together these four Prelude modules define
181 import GHC.Handle -- all the stuff exported by IO for the GHC version
193 import Hugs.Prelude ( throw, Exception(NonTermination) )
194 import Control.Exception ( bracket )
195 import System.IO.Unsafe ( unsafeInterleaveIO )
202 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
203 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
204 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
205 , stdin, stdout, stderr
206 , openFile -- :: FilePath -> IOMode -> IO Handle
207 , hClose -- :: Handle -> IO ()
208 , hFileSize -- :: Handle -> IO Integer
209 , hIsEOF -- :: Handle -> IO Bool
210 , isEOF -- :: IO Bool
211 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
212 , hGetBuffering -- :: Handle -> IO BufferMode
213 , hFlush -- :: Handle -> IO ()
214 , hGetPosn -- :: Handle -> IO HandlePosn
215 , hSetPosn -- :: HandlePosn -> IO ()
216 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
217 , hWaitForInput -- :: Handle -> Int -> IO Bool
218 , hGetChar -- :: Handle -> IO Char
219 , hGetLine -- :: Handle -> IO [Char]
220 , hLookAhead -- :: Handle -> IO Char
221 , hGetContents -- :: Handle -> IO [Char]
222 , hPutChar -- :: Handle -> Char -> IO ()
223 , hPutStr -- :: Handle -> [Char] -> IO ()
224 , hPutStrLn -- :: Handle -> [Char] -> IO ()
225 , hPrint -- :: Handle -> [Char] -> IO ()
226 , hReady -- :: Handle -> [Char] -> IO ()
227 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
228 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
229 , hIsSeekable -- :: Handle -> IO Bool
233 , FilePath -- :: String
235 import NHC.IOExtras (fixIO, hPutBuf, hGetBuf)
239 -- -----------------------------------------------------------------------------
242 #ifdef __GLASGOW_HASKELL__
243 -- | Write a character to the standard output device
244 -- (same as 'hPutChar' 'stdout').
246 putChar :: Char -> IO ()
247 putChar c = hPutChar stdout c
249 -- | Write a string to the standard output device
250 -- (same as 'hPutStr' 'stdout').
252 putStr :: String -> IO ()
253 putStr s = hPutStr stdout s
255 -- | The same as 'putStr', but adds a newline character.
257 putStrLn :: String -> IO ()
258 putStrLn s = do putStr s
261 -- | The 'print' function outputs a value of any printable type to the
262 -- standard output device.
263 -- Printable types are those that are instances of class 'Show'; 'print'
264 -- converts values to strings for output using the 'show' operation and
267 -- For example, a program to print the first 20 integers and their
268 -- powers of 2 could be written as:
270 -- > main = print ([(n, 2^n) | n <- [0..19]])
272 print :: Show a => a -> IO ()
273 print x = putStrLn (show x)
275 -- | Read a character from the standard input device
276 -- (same as 'hGetChar' 'stdin').
279 getChar = hGetChar stdin
281 -- | Read a line from the standard input device
282 -- (same as 'hGetLine' 'stdin').
285 getLine = hGetLine stdin
287 -- | The 'getContents' operation returns all user input as a single string,
288 -- which is read lazily as it is needed
289 -- (same as 'hGetContents' 'stdin').
291 getContents :: IO String
292 getContents = hGetContents stdin
294 -- | The 'interact' function takes a function of type @String->String@
295 -- as its argument. The entire input from the standard input device is
296 -- passed to this function as its argument, and the resulting string is
297 -- output on the standard output device.
299 interact :: (String -> String) -> IO ()
300 interact f = do s <- getContents
303 -- | The 'readFile' function reads a file and
304 -- returns the contents of the file as a string.
305 -- The file is read lazily, on demand, as with 'getContents'.
307 readFile :: FilePath -> IO String
308 readFile name = openFile name ReadMode >>= hGetContents
310 -- | The computation 'writeFile' @file str@ function writes the string @str@,
311 -- to the file @file@.
312 writeFile :: FilePath -> String -> IO ()
313 writeFile f txt = withFile f WriteMode (\ hdl -> hPutStr hdl txt)
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 f txt = withFile f AppendMode (\ hdl -> hPutStr hdl txt)
327 -- | The 'readLn' function combines 'getLine' and 'readIO'.
329 readLn :: Read a => IO a
330 readLn = do l <- getLine
334 -- | The 'readIO' function is similar to 'read' except that it signals
335 -- parse failure to the 'IO' monad instead of terminating the program.
337 readIO :: Read a => String -> IO a
338 readIO s = case (do { (x,t) <- reads s ;
342 [] -> ioError (userError "Prelude.readIO: no parse")
343 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
344 #endif /* __GLASGOW_HASKELL__ */
347 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
348 -- available for input from handle @hdl@.
350 -- This operation may fail with:
352 -- * 'System.IO.Error.isEOFError' if the end of file has been reached.
354 hReady :: Handle -> IO Bool
355 hReady h = hWaitForInput h 0
357 -- | The same as 'hPutStr', but adds a newline character.
359 hPutStrLn :: Handle -> String -> IO ()
360 hPutStrLn hndl str = do
364 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
365 -- given by the 'shows' function to the file or channel managed by @hdl@
366 -- and appends a newline.
368 -- This operation may fail with:
370 -- * 'System.IO.Error.isFullError' if the device is full; or
372 -- * 'System.IO.Error.isPermissionError' if another system resource limit would be exceeded.
374 hPrint :: Show a => Handle -> a -> IO ()
375 hPrint hdl = hPutStrLn hdl . show
376 #endif /* !__NHC__ */
378 -- | @'withFile' name mode act@ opens a file using 'openFile' and passes
379 -- the resulting handle to the computation @act@. The handle will be
380 -- closed on exit from 'withFile', whether by normal termination or by
381 -- raising an exception.
382 withFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
383 withFile name mode = bracket (openFile name mode) hClose
385 -- | @'withBinaryFile' name mode act@ opens a file using 'openBinaryFile'
386 -- and passes the resulting handle to the computation @act@. The handle
387 -- will be closed on exit from 'withBinaryFile', whether by normal
388 -- termination or by raising an exception.
389 withBinaryFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
390 withBinaryFile name mode = bracket (openBinaryFile name mode) hClose
392 -- ---------------------------------------------------------------------------
395 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
396 fixIO :: (a -> IO a) -> IO a
398 ref <- newIORef (throw NonTermination)
399 ans <- unsafeInterleaveIO (readIORef ref)
401 writeIORef ref result
404 -- NOTE: we do our own explicit black holing here, because GHC's lazy
405 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
406 -- computation a few times before it notices the loop, which is wrong.
410 -- Assume a unix platform, where text and binary I/O are identical.
411 openBinaryFile = openFile
412 hSetBinaryMode _ _ = return ()
415 -- | The function creates a temporary file in ReadWrite mode.
416 -- The created file isn\'t deleted automatically, so you need to delete it manually.
417 openTempFile :: FilePath -- ^ Directory in which to create the file
418 -> String -- ^ File name template. If the template is \"foo.ext\" then
419 -- the create file will be \"fooXXX.ext\" where XXX is some
421 -> IO (FilePath, Handle)
422 openTempFile tmp_dir template = openTempFile' "openTempFile" tmp_dir template False
424 -- | Like 'openTempFile', but opens the file in binary mode. See 'openBinaryFile' for more comments.
425 openBinaryTempFile :: FilePath -> String -> IO (FilePath, Handle)
426 openBinaryTempFile tmp_dir template = openTempFile' "openBinaryTempFile" tmp_dir template True
428 openTempFile' :: String -> FilePath -> String -> Bool -> IO (FilePath, Handle)
429 openTempFile' loc tmp_dir template binary = do
433 -- We split off the last extension, so we can use .foo.ext files
434 -- for temporary files (hidden on Unix OSes). Unfortunately we're
435 -- below filepath in the hierarchy here.
436 (prefix,suffix) = case break (== '.') $ reverse template of
437 (rev_suffix, rev_prefix) ->
438 (reverse rev_prefix, reverse rev_suffix)
440 oflags1 = rw_flags .|. o_EXCL
446 oflags = oflags1 .|. binary_flags
449 fd <- withCString filepath $ \ f ->
450 c_open f oflags 0o666
455 then findTempName (x+1)
456 else ioError (errnoToIOError loc errno Nothing (Just tmp_dir))
458 -- XXX We want to tell fdToHandle what the filepath is,
459 -- as any exceptions etc will only be able to report the
462 `ExceptionBase.catchException` \e -> do c_close fd; throw e
465 filename = prefix ++ show x ++ suffix
466 filepath = tmp_dir ++ [pathSeparator] ++ filename
468 fdToHandle fd = openFd (fromIntegral fd) False ReadWriteMode binary
471 -- XXX Should use filepath library
472 pathSeparator :: Char
473 #ifdef mingw32_HOST_OS
479 -- XXX Copied from GHC.Handle
480 std_flags = o_NONBLOCK .|. o_NOCTTY
481 output_flags = std_flags .|. o_CREAT
482 read_flags = std_flags .|. o_RDONLY
483 write_flags = output_flags .|. o_WRONLY
484 rw_flags = output_flags .|. o_RDWR
485 append_flags = write_flags .|. o_APPEND
488 -- Implementations should enforce as far as possible, at least locally to the
489 -- Haskell process, multiple-reader single-writer locking on files.
490 -- That is, /there may either be many handles on the same file which manage
491 -- input, or just one handle on the file which manages output/. If any
492 -- open or semi-closed handle is managing a file for output, no new
493 -- handle can be allocated for that file. If any open or semi-closed
494 -- handle is managing a file for input, new handles can only be allocated
495 -- if they do not manage output. Whether two files are the same is
496 -- implementation-dependent, but they should normally be the same if they
497 -- have the same absolute path name and neither has been renamed, for
500 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
501 -- the file until the entire contents of the file have been consumed.
502 -- It follows that an attempt to write to a file (using 'writeFile', for
503 -- example) that was earlier opened by 'readFile' will usually result in
504 -- failure with 'System.IO.Error.isAlreadyInUseError'.
506 -- -----------------------------------------------------------------------------
509 #ifdef __GLASGOW_HASKELL__
510 -- Copied here to avoid recursive dependency with Control.Exception
512 :: IO a -- ^ computation to run first (\"acquire resource\")
513 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
514 -> (a -> IO c) -- ^ computation to run in-between
515 -> IO c -- returns the value from the in-between computation
516 bracket before after thing =
521 (\e -> do { after a; throw e })