1 {-# OPTIONS_GHC -XNoImplicitPrelude #-}
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 (not portable: GHC\/Hugs only)
100 #if !defined(__NHC__)
101 hIsTerminalDevice, -- :: Handle -> IO Bool
103 hSetEcho, -- :: Handle -> Bool -> IO ()
104 hGetEcho, -- :: Handle -> IO Bool
107 -- ** Showing handle state (not portable: GHC only)
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
164 import Control.Exception hiding (bracket)
170 import Foreign.C.Error
171 import Foreign.C.String
172 import System.Posix.Internals
175 #ifdef __GLASGOW_HASKELL__
176 import GHC.IOBase as ExceptionBase
179 import Hugs.Exception as ExceptionBase
182 #ifdef __GLASGOW_HASKELL__
184 import GHC.IOBase -- Together these four Prelude modules define
185 import GHC.Handle -- all the stuff exported by IO for the GHC version
197 import Hugs.Prelude ( throw, Exception(NonTermination) )
198 import Control.Exception ( bracket )
199 import System.IO.Unsafe ( unsafeInterleaveIO )
206 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
207 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
208 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
209 , stdin, stdout, stderr
210 , openFile -- :: FilePath -> IOMode -> IO Handle
211 , hClose -- :: Handle -> IO ()
212 , hFileSize -- :: Handle -> IO Integer
213 , hIsEOF -- :: Handle -> IO Bool
214 , isEOF -- :: IO Bool
215 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
216 , hGetBuffering -- :: Handle -> IO BufferMode
217 , hFlush -- :: Handle -> IO ()
218 , hGetPosn -- :: Handle -> IO HandlePosn
219 , hSetPosn -- :: HandlePosn -> IO ()
220 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
221 , hWaitForInput -- :: Handle -> Int -> IO Bool
222 , hGetChar -- :: Handle -> IO Char
223 , hGetLine -- :: Handle -> IO [Char]
224 , hLookAhead -- :: Handle -> IO Char
225 , hGetContents -- :: Handle -> IO [Char]
226 , hPutChar -- :: Handle -> Char -> IO ()
227 , hPutStr -- :: Handle -> [Char] -> IO ()
228 , hPutStrLn -- :: Handle -> [Char] -> IO ()
229 , hPrint -- :: Handle -> [Char] -> IO ()
230 , hReady -- :: Handle -> [Char] -> IO ()
231 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
232 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
233 , hIsSeekable -- :: Handle -> IO Bool
237 , FilePath -- :: String
239 import NHC.IOExtras (fixIO, hPutBuf, hGetBuf)
243 -- -----------------------------------------------------------------------------
246 #ifdef __GLASGOW_HASKELL__
247 -- | Write a character to the standard output device
248 -- (same as 'hPutChar' 'stdout').
250 putChar :: Char -> IO ()
251 putChar c = hPutChar stdout c
253 -- | Write a string to the standard output device
254 -- (same as 'hPutStr' 'stdout').
256 putStr :: String -> IO ()
257 putStr s = hPutStr stdout s
259 -- | The same as 'putStr', but adds a newline character.
261 putStrLn :: String -> IO ()
262 putStrLn s = do putStr s
265 -- | The 'print' function outputs a value of any printable type to the
266 -- standard output device.
267 -- Printable types are those that are instances of class 'Show'; 'print'
268 -- converts values to strings for output using the 'show' operation and
271 -- For example, a program to print the first 20 integers and their
272 -- powers of 2 could be written as:
274 -- > main = print ([(n, 2^n) | n <- [0..19]])
276 print :: Show a => a -> IO ()
277 print x = putStrLn (show x)
279 -- | Read a character from the standard input device
280 -- (same as 'hGetChar' 'stdin').
283 getChar = hGetChar stdin
285 -- | Read a line from the standard input device
286 -- (same as 'hGetLine' 'stdin').
289 getLine = hGetLine stdin
291 -- | The 'getContents' operation returns all user input as a single string,
292 -- which is read lazily as it is needed
293 -- (same as 'hGetContents' 'stdin').
295 getContents :: IO String
296 getContents = hGetContents stdin
298 -- | The 'interact' function takes a function of type @String->String@
299 -- as its argument. The entire input from the standard input device is
300 -- passed to this function as its argument, and the resulting string is
301 -- output on the standard output device.
303 interact :: (String -> String) -> IO ()
304 interact f = do s <- getContents
307 -- | The 'readFile' function reads a file and
308 -- returns the contents of the file as a string.
309 -- The file is read lazily, on demand, as with 'getContents'.
311 readFile :: FilePath -> IO String
312 readFile name = openFile name ReadMode >>= hGetContents
314 -- | The computation 'writeFile' @file str@ function writes the string @str@,
315 -- to the file @file@.
316 writeFile :: FilePath -> String -> IO ()
317 writeFile f txt = withFile f WriteMode (\ hdl -> hPutStr hdl txt)
319 -- | The computation 'appendFile' @file str@ function appends the string @str@,
320 -- to the file @file@.
322 -- Note that 'writeFile' and 'appendFile' write a literal string
323 -- to a file. To write a value of any printable type, as with 'print',
324 -- use the 'show' function to convert the value to a string first.
326 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
328 appendFile :: FilePath -> String -> IO ()
329 appendFile f txt = withFile f AppendMode (\ hdl -> hPutStr hdl txt)
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 -- * 'System.IO.Error.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 -- * 'System.IO.Error.isFullError' if the device is full; or
376 -- * 'System.IO.Error.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 -- | @'withFile' name mode act@ opens a file using 'openFile' and passes
383 -- the resulting handle to the computation @act@. The handle will be
384 -- closed on exit from 'withFile', whether by normal termination or by
385 -- raising an exception.
386 withFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
387 withFile name mode = bracket (openFile name mode) hClose
389 -- | @'withBinaryFile' name mode act@ opens a file using 'openBinaryFile'
390 -- and passes the resulting handle to the computation @act@. The handle
391 -- will be closed on exit from 'withBinaryFile', whether by normal
392 -- termination or by raising an exception.
393 withBinaryFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
394 withBinaryFile name mode = bracket (openBinaryFile name mode) hClose
396 -- ---------------------------------------------------------------------------
399 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
400 fixIO :: (a -> IO a) -> IO a
402 ref <- newIORef (throw NonTermination)
403 ans <- unsafeInterleaveIO (readIORef ref)
405 writeIORef ref result
408 -- NOTE: we do our own explicit black holing here, because GHC's lazy
409 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
410 -- computation a few times before it notices the loop, which is wrong.
414 -- Assume a unix platform, where text and binary I/O are identical.
415 openBinaryFile = openFile
416 hSetBinaryMode _ _ = return ()
419 -- | The function creates a temporary file in ReadWrite mode.
420 -- The created file isn\'t deleted automatically, so you need to delete it manually.
422 -- The file is creates with permissions such that only the current
423 -- user can read\/write it.
425 -- With some exceptions (see below), the file will be created securely
426 -- in the sense that an attacker should not be able to cause
427 -- openTempFile to overwrite another file on the filesystem using your
428 -- credentials, by putting symbolic links (on Unix) in the place where
429 -- the temporary file is to be created. On Unix the @O_CREAT@ and
430 -- @O_EXCL@ flags are used to prevent this attack, but note that
431 -- @O_EXCL@ is sometimes not supported on NFS filesystems, so if you
432 -- rely on this behaviour it is best to use local filesystems only.
434 openTempFile :: FilePath -- ^ Directory in which to create the file
435 -> String -- ^ File name template. If the template is \"foo.ext\" then
436 -- the created file will be \"fooXXX.ext\" where XXX is some
438 -> IO (FilePath, Handle)
439 openTempFile tmp_dir template = openTempFile' "openTempFile" tmp_dir template False
441 -- | Like 'openTempFile', but opens the file in binary mode. See 'openBinaryFile' for more comments.
442 openBinaryTempFile :: FilePath -> String -> IO (FilePath, Handle)
443 openBinaryTempFile tmp_dir template = openTempFile' "openBinaryTempFile" tmp_dir template True
445 openTempFile' :: String -> FilePath -> String -> Bool -> IO (FilePath, Handle)
446 openTempFile' loc tmp_dir template binary = do
450 -- We split off the last extension, so we can use .foo.ext files
451 -- for temporary files (hidden on Unix OSes). Unfortunately we're
452 -- below filepath in the hierarchy here.
454 case break (== '.') $ reverse template of
455 -- First case: template contains no '.'s. Just re-reverse it.
456 (rev_suffix, "") -> (reverse rev_suffix, "")
457 -- Second case: template contains at least one '.'. Strip the
458 -- dot from the prefix and prepend it to the suffix (if we don't
459 -- do this, the unique number will get added after the '.' and
460 -- thus be part of the extension, which is wrong.)
461 (rev_suffix, '.':rest) -> (reverse rest, '.':reverse rev_suffix)
462 -- Otherwise, something is wrong, because (break (== '.')) should
463 -- always return a pair with either the empty string or a string
464 -- beginning with '.' as the second component.
465 _ -> error "bug in System.IO.openTempFile"
468 oflags1 = rw_flags .|. o_EXCL
474 oflags = oflags1 .|. binary_flags
478 findTempName x = do h <- openFile filepath ReadWriteMode
482 fd <- withCString filepath $ \ f ->
483 c_open f oflags 0o600
488 then findTempName (x+1)
489 else ioError (errnoToIOError loc errno Nothing (Just tmp_dir))
491 -- XXX We want to tell fdToHandle what the filepath is,
492 -- as any exceptions etc will only be able to report the
495 `ExceptionBase.catchAny` \e -> do c_close fd; throw e
499 filename = prefix ++ show x ++ suffix
500 filepath = tmp_dir `combine` filename
502 -- XXX bits copied from System.FilePath, since that's not available here
506 | last a == pathSeparator = a ++ b
507 | otherwise = a ++ [pathSeparator] ++ b
510 fdToHandle fd = openFd (fromIntegral fd) False ReadWriteMode binary
513 -- XXX Should use filepath library
514 pathSeparator :: Char
515 #ifdef mingw32_HOST_OS
522 -- XXX Copied from GHC.Handle
523 std_flags = o_NONBLOCK .|. o_NOCTTY
524 output_flags = std_flags .|. o_CREAT
525 read_flags = std_flags .|. o_RDONLY
526 write_flags = output_flags .|. o_WRONLY
527 rw_flags = output_flags .|. o_RDWR
528 append_flags = write_flags .|. o_APPEND
532 foreign import ccall "getpid" c_getpid :: IO Int
536 -- Implementations should enforce as far as possible, at least locally to the
537 -- Haskell process, multiple-reader single-writer locking on files.
538 -- That is, /there may either be many handles on the same file which manage
539 -- input, or just one handle on the file which manages output/. If any
540 -- open or semi-closed handle is managing a file for output, no new
541 -- handle can be allocated for that file. If any open or semi-closed
542 -- handle is managing a file for input, new handles can only be allocated
543 -- if they do not manage output. Whether two files are the same is
544 -- implementation-dependent, but they should normally be the same if they
545 -- have the same absolute path name and neither has been renamed, for
548 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
549 -- the file until the entire contents of the file have been consumed.
550 -- It follows that an attempt to write to a file (using 'writeFile', for
551 -- example) that was earlier opened by 'readFile' will usually result in
552 -- failure with 'System.IO.Error.isAlreadyInUseError'.
554 -- -----------------------------------------------------------------------------
557 #ifdef __GLASGOW_HASKELL__
558 -- Copied here to avoid recursive dependency with Control.Exception
560 :: IO a -- ^ computation to run first (\"acquire resource\")
561 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
562 -> (a -> IO c) -- ^ computation to run in-between
563 -> IO c -- returns the value from the in-between computation
564 bracket before after thing =
569 (\e -> do { after a; throw e })