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.Base
170 import Foreign.C.Error
171 import Foreign.C.String
172 import System.Posix.Internals
175 #ifdef __GLASGOW_HASKELL__
177 import GHC.IOBase -- Together these four Prelude modules define
178 import GHC.Handle -- all the stuff exported by IO for the GHC version
190 import System.IO.Unsafe ( unsafeInterleaveIO )
197 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
198 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
199 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
200 , stdin, stdout, stderr
201 , openFile -- :: FilePath -> IOMode -> IO Handle
202 , hClose -- :: Handle -> IO ()
203 , hFileSize -- :: Handle -> IO Integer
204 , hIsEOF -- :: Handle -> IO Bool
205 , isEOF -- :: IO Bool
206 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
207 , hGetBuffering -- :: Handle -> IO BufferMode
208 , hFlush -- :: Handle -> IO ()
209 , hGetPosn -- :: Handle -> IO HandlePosn
210 , hSetPosn -- :: HandlePosn -> IO ()
211 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
212 , hWaitForInput -- :: Handle -> Int -> IO Bool
213 , hGetChar -- :: Handle -> IO Char
214 , hGetLine -- :: Handle -> IO [Char]
215 , hLookAhead -- :: Handle -> IO Char
216 , hGetContents -- :: Handle -> IO [Char]
217 , hPutChar -- :: Handle -> Char -> IO ()
218 , hPutStr -- :: Handle -> [Char] -> IO ()
219 , hPutStrLn -- :: Handle -> [Char] -> IO ()
220 , hPrint -- :: Handle -> [Char] -> IO ()
221 , hReady -- :: Handle -> [Char] -> IO ()
222 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
223 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
224 , hIsSeekable -- :: Handle -> IO Bool
228 , FilePath -- :: String
230 import NHC.IOExtras (fixIO, hPutBuf, hGetBuf)
234 -- -----------------------------------------------------------------------------
237 #ifdef __GLASGOW_HASKELL__
238 -- | Write a character to the standard output device
239 -- (same as 'hPutChar' 'stdout').
241 putChar :: Char -> IO ()
242 putChar c = hPutChar stdout c
244 -- | Write a string to the standard output device
245 -- (same as 'hPutStr' 'stdout').
247 putStr :: String -> IO ()
248 putStr s = hPutStr stdout s
250 -- | The same as 'putStr', but adds a newline character.
252 putStrLn :: String -> IO ()
253 putStrLn s = do putStr s
256 -- | The 'print' function outputs a value of any printable type to the
257 -- standard output device.
258 -- Printable types are those that are instances of class 'Show'; 'print'
259 -- converts values to strings for output using the 'show' operation and
262 -- For example, a program to print the first 20 integers and their
263 -- powers of 2 could be written as:
265 -- > main = print ([(n, 2^n) | n <- [0..19]])
267 print :: Show a => a -> IO ()
268 print x = putStrLn (show x)
270 -- | Read a character from the standard input device
271 -- (same as 'hGetChar' 'stdin').
274 getChar = hGetChar stdin
276 -- | Read a line from the standard input device
277 -- (same as 'hGetLine' 'stdin').
280 getLine = hGetLine stdin
282 -- | The 'getContents' operation returns all user input as a single string,
283 -- which is read lazily as it is needed
284 -- (same as 'hGetContents' 'stdin').
286 getContents :: IO String
287 getContents = hGetContents stdin
289 -- | The 'interact' function takes a function of type @String->String@
290 -- as its argument. The entire input from the standard input device is
291 -- passed to this function as its argument, and the resulting string is
292 -- output on the standard output device.
294 interact :: (String -> String) -> IO ()
295 interact f = do s <- getContents
298 -- | The 'readFile' function reads a file and
299 -- returns the contents of the file as a string.
300 -- The file is read lazily, on demand, as with 'getContents'.
302 readFile :: FilePath -> IO String
303 readFile name = openFile name ReadMode >>= hGetContents
305 -- | The computation 'writeFile' @file str@ function writes the string @str@,
306 -- to the file @file@.
307 writeFile :: FilePath -> String -> IO ()
308 writeFile f txt = withFile f WriteMode (\ hdl -> hPutStr hdl txt)
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 f txt = withFile f AppendMode (\ hdl -> hPutStr hdl txt)
322 -- | The 'readLn' function combines 'getLine' and 'readIO'.
324 readLn :: Read a => IO a
325 readLn = do l <- getLine
329 -- | The 'readIO' function is similar to 'read' except that it signals
330 -- parse failure to the 'IO' monad instead of terminating the program.
332 readIO :: Read a => String -> IO a
333 readIO s = case (do { (x,t) <- reads s ;
337 [] -> ioError (userError "Prelude.readIO: no parse")
338 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
339 #endif /* __GLASGOW_HASKELL__ */
342 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
343 -- available for input from handle @hdl@.
345 -- This operation may fail with:
347 -- * 'System.IO.Error.isEOFError' if the end of file has been reached.
349 hReady :: Handle -> IO Bool
350 hReady h = hWaitForInput h 0
352 -- | The same as 'hPutStr', but adds a newline character.
354 hPutStrLn :: Handle -> String -> IO ()
355 hPutStrLn hndl str = do
359 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
360 -- given by the 'shows' function to the file or channel managed by @hdl@
361 -- and appends a newline.
363 -- This operation may fail with:
365 -- * 'System.IO.Error.isFullError' if the device is full; or
367 -- * 'System.IO.Error.isPermissionError' if another system resource limit would be exceeded.
369 hPrint :: Show a => Handle -> a -> IO ()
370 hPrint hdl = hPutStrLn hdl . show
371 #endif /* !__NHC__ */
373 -- | @'withFile' name mode act@ opens a file using 'openFile' and passes
374 -- the resulting handle to the computation @act@. The handle will be
375 -- closed on exit from 'withFile', whether by normal termination or by
376 -- raising an exception.
377 withFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
378 withFile name mode = bracket (openFile name mode) hClose
380 -- | @'withBinaryFile' name mode act@ opens a file using 'openBinaryFile'
381 -- and passes the resulting handle to the computation @act@. The handle
382 -- will be closed on exit from 'withBinaryFile', whether by normal
383 -- termination or by raising an exception.
384 withBinaryFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
385 withBinaryFile name mode = bracket (openBinaryFile name mode) hClose
387 -- ---------------------------------------------------------------------------
390 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
391 fixIO :: (a -> IO a) -> IO a
393 ref <- newIORef (throw NonTermination)
394 ans <- unsafeInterleaveIO (readIORef ref)
396 writeIORef ref result
399 -- NOTE: we do our own explicit black holing here, because GHC's lazy
400 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
401 -- computation a few times before it notices the loop, which is wrong.
405 -- Assume a unix platform, where text and binary I/O are identical.
406 openBinaryFile = openFile
407 hSetBinaryMode _ _ = return ()
410 -- | The function creates a temporary file in ReadWrite mode.
411 -- The created file isn\'t deleted automatically, so you need to delete it manually.
413 -- The file is creates with permissions such that only the current
414 -- user can read\/write it.
416 -- With some exceptions (see below), the file will be created securely
417 -- in the sense that an attacker should not be able to cause
418 -- openTempFile to overwrite another file on the filesystem using your
419 -- credentials, by putting symbolic links (on Unix) in the place where
420 -- the temporary file is to be created. On Unix the @O_CREAT@ and
421 -- @O_EXCL@ flags are used to prevent this attack, but note that
422 -- @O_EXCL@ is sometimes not supported on NFS filesystems, so if you
423 -- rely on this behaviour it is best to use local filesystems only.
425 openTempFile :: FilePath -- ^ Directory in which to create the file
426 -> String -- ^ File name template. If the template is \"foo.ext\" then
427 -- the created file will be \"fooXXX.ext\" where XXX is some
429 -> IO (FilePath, Handle)
430 openTempFile tmp_dir template = openTempFile' "openTempFile" tmp_dir template False
432 -- | Like 'openTempFile', but opens the file in binary mode. See 'openBinaryFile' for more comments.
433 openBinaryTempFile :: FilePath -> String -> IO (FilePath, Handle)
434 openBinaryTempFile tmp_dir template = openTempFile' "openBinaryTempFile" tmp_dir template True
436 openTempFile' :: String -> FilePath -> String -> Bool -> IO (FilePath, Handle)
437 openTempFile' loc tmp_dir template binary = do
441 -- We split off the last extension, so we can use .foo.ext files
442 -- for temporary files (hidden on Unix OSes). Unfortunately we're
443 -- below filepath in the hierarchy here.
445 case break (== '.') $ reverse template of
446 -- First case: template contains no '.'s. Just re-reverse it.
447 (rev_suffix, "") -> (reverse rev_suffix, "")
448 -- Second case: template contains at least one '.'. Strip the
449 -- dot from the prefix and prepend it to the suffix (if we don't
450 -- do this, the unique number will get added after the '.' and
451 -- thus be part of the extension, which is wrong.)
452 (rev_suffix, '.':rest) -> (reverse rest, '.':reverse rev_suffix)
453 -- Otherwise, something is wrong, because (break (== '.')) should
454 -- always return a pair with either the empty string or a string
455 -- beginning with '.' as the second component.
456 _ -> error "bug in System.IO.openTempFile"
459 oflags1 = rw_flags .|. o_EXCL
465 oflags = oflags1 .|. binary_flags
469 findTempName x = do h <- openFile filepath ReadWriteMode
473 fd <- withCString filepath $ \ f ->
474 c_open f oflags 0o600
479 then findTempName (x+1)
480 else ioError (errnoToIOError loc errno Nothing (Just tmp_dir))
482 -- XXX We want to tell fdToHandle what the filepath is,
483 -- as any exceptions etc will only be able to report the
485 h <- fdToHandle fd `onException` c_close fd
489 filename = prefix ++ show x ++ suffix
490 filepath = tmp_dir `combine` filename
492 -- XXX bits copied from System.FilePath, since that's not available here
496 | last a == pathSeparator = a ++ b
497 | otherwise = a ++ [pathSeparator] ++ b
500 fdToHandle fd = openFd (fromIntegral fd) False ReadWriteMode binary
503 -- XXX Should use filepath library
504 pathSeparator :: Char
505 #ifdef mingw32_HOST_OS
512 -- XXX Copied from GHC.Handle
513 std_flags = o_NONBLOCK .|. o_NOCTTY
514 output_flags = std_flags .|. o_CREAT
515 read_flags = std_flags .|. o_RDONLY
516 write_flags = output_flags .|. o_WRONLY
517 rw_flags = output_flags .|. o_RDWR
518 append_flags = write_flags .|. o_APPEND
522 foreign import ccall "getpid" c_getpid :: IO Int
526 -- Implementations should enforce as far as possible, at least locally to the
527 -- Haskell process, multiple-reader single-writer locking on files.
528 -- That is, /there may either be many handles on the same file which manage
529 -- input, or just one handle on the file which manages output/. If any
530 -- open or semi-closed handle is managing a file for output, no new
531 -- handle can be allocated for that file. If any open or semi-closed
532 -- handle is managing a file for input, new handles can only be allocated
533 -- if they do not manage output. Whether two files are the same is
534 -- implementation-dependent, but they should normally be the same if they
535 -- have the same absolute path name and neither has been renamed, for
538 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
539 -- the file until the entire contents of the file have been consumed.
540 -- It follows that an attempt to write to a file (using 'writeFile', for
541 -- example) that was earlier opened by 'readFile' will usually result in
542 -- failure with 'System.IO.Error.isAlreadyInUseError'.