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.Types
172 import System.Posix.Internals
175 #ifdef __GLASGOW_HASKELL__
177 import GHC.IO hiding ( onException )
179 import GHC.IO.Handle.FD
182 import GHC.IO.Exception ( userError )
193 import System.IO.Unsafe ( unsafeInterleaveIO )
200 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
201 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
202 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
203 , stdin, stdout, stderr
204 , openFile -- :: FilePath -> IOMode -> IO Handle
205 , hClose -- :: Handle -> IO ()
206 , hFileSize -- :: Handle -> IO Integer
207 , hIsEOF -- :: Handle -> IO Bool
208 , isEOF -- :: IO Bool
209 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
210 , hGetBuffering -- :: Handle -> IO BufferMode
211 , hFlush -- :: Handle -> IO ()
212 , hGetPosn -- :: Handle -> IO HandlePosn
213 , hSetPosn -- :: HandlePosn -> IO ()
214 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
215 , hWaitForInput -- :: Handle -> Int -> IO Bool
216 , hGetChar -- :: Handle -> IO Char
217 , hGetLine -- :: Handle -> IO [Char]
218 , hLookAhead -- :: Handle -> IO Char
219 , hGetContents -- :: Handle -> IO [Char]
220 , hPutChar -- :: Handle -> Char -> IO ()
221 , hPutStr -- :: Handle -> [Char] -> IO ()
222 , hPutStrLn -- :: Handle -> [Char] -> IO ()
223 , hPrint -- :: Handle -> [Char] -> IO ()
224 , hReady -- :: Handle -> [Char] -> IO ()
225 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
226 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
227 , hIsSeekable -- :: Handle -> IO Bool
231 , FilePath -- :: String
233 import NHC.IOExtras (fixIO, hPutBuf, hGetBuf)
237 -- -----------------------------------------------------------------------------
240 #ifdef __GLASGOW_HASKELL__
241 -- | Write a character to the standard output device
242 -- (same as 'hPutChar' 'stdout').
244 putChar :: Char -> IO ()
245 putChar c = hPutChar stdout c
247 -- | Write a string to the standard output device
248 -- (same as 'hPutStr' 'stdout').
250 putStr :: String -> IO ()
251 putStr s = hPutStr stdout s
253 -- | The same as 'putStr', but adds a newline character.
255 putStrLn :: String -> IO ()
256 putStrLn s = do putStr s
259 -- | The 'print' function outputs a value of any printable type to the
260 -- standard output device.
261 -- Printable types are those that are instances of class 'Show'; 'print'
262 -- converts values to strings for output using the 'show' operation and
265 -- For example, a program to print the first 20 integers and their
266 -- powers of 2 could be written as:
268 -- > main = print ([(n, 2^n) | n <- [0..19]])
270 print :: Show a => a -> IO ()
271 print x = putStrLn (show x)
273 -- | Read a character from the standard input device
274 -- (same as 'hGetChar' 'stdin').
277 getChar = hGetChar stdin
279 -- | Read a line from the standard input device
280 -- (same as 'hGetLine' 'stdin').
283 getLine = hGetLine stdin
285 -- | The 'getContents' operation returns all user input as a single string,
286 -- which is read lazily as it is needed
287 -- (same as 'hGetContents' 'stdin').
289 getContents :: IO String
290 getContents = hGetContents stdin
292 -- | The 'interact' function takes a function of type @String->String@
293 -- as its argument. The entire input from the standard input device is
294 -- passed to this function as its argument, and the resulting string is
295 -- output on the standard output device.
297 interact :: (String -> String) -> IO ()
298 interact f = do s <- getContents
301 -- | The 'readFile' function reads a file and
302 -- returns the contents of the file as a string.
303 -- The file is read lazily, on demand, as with 'getContents'.
305 readFile :: FilePath -> IO String
306 readFile name = openFile name ReadMode >>= hGetContents
308 -- | The computation 'writeFile' @file str@ function writes the string @str@,
309 -- to the file @file@.
310 writeFile :: FilePath -> String -> IO ()
311 writeFile f txt = withFile f WriteMode (\ hdl -> hPutStr hdl txt)
313 -- | The computation 'appendFile' @file str@ function appends the string @str@,
314 -- to the file @file@.
316 -- Note that 'writeFile' and 'appendFile' write a literal string
317 -- to a file. To write a value of any printable type, as with 'print',
318 -- use the 'show' function to convert the value to a string first.
320 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
322 appendFile :: FilePath -> String -> IO ()
323 appendFile f txt = withFile f AppendMode (\ hdl -> hPutStr hdl txt)
325 -- | The 'readLn' function combines 'getLine' and 'readIO'.
327 readLn :: Read a => IO a
328 readLn = do l <- getLine
332 -- | The 'readIO' function is similar to 'read' except that it signals
333 -- parse failure to the 'IO' monad instead of terminating the program.
335 readIO :: Read a => String -> IO a
336 readIO s = case (do { (x,t) <- reads s ;
340 [] -> ioError (userError "Prelude.readIO: no parse")
341 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
342 #endif /* __GLASGOW_HASKELL__ */
345 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
346 -- available for input from handle @hdl@.
348 -- This operation may fail with:
350 -- * 'System.IO.Error.isEOFError' if the end of file has been reached.
352 hReady :: Handle -> IO Bool
353 hReady h = hWaitForInput h 0
355 -- | The same as 'hPutStr', but adds a newline character.
357 hPutStrLn :: Handle -> String -> IO ()
358 hPutStrLn hndl str = do
362 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
363 -- given by the 'shows' function to the file or channel managed by @hdl@
364 -- and appends a newline.
366 -- This operation may fail with:
368 -- * 'System.IO.Error.isFullError' if the device is full; or
370 -- * 'System.IO.Error.isPermissionError' if another system resource limit would be exceeded.
372 hPrint :: Show a => Handle -> a -> IO ()
373 hPrint hdl = hPutStrLn hdl . show
374 #endif /* !__NHC__ */
376 -- | @'withFile' name mode act@ opens a file using 'openFile' and passes
377 -- the resulting handle to the computation @act@. The handle will be
378 -- closed on exit from 'withFile', whether by normal termination or by
379 -- raising an exception.
380 withFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
381 withFile name mode = bracket (openFile name mode) hClose
383 -- | @'withBinaryFile' name mode act@ opens a file using 'openBinaryFile'
384 -- and passes the resulting handle to the computation @act@. The handle
385 -- will be closed on exit from 'withBinaryFile', whether by normal
386 -- termination or by raising an exception.
387 withBinaryFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
388 withBinaryFile name mode = bracket (openBinaryFile name mode) hClose
390 -- ---------------------------------------------------------------------------
393 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
394 fixIO :: (a -> IO a) -> IO a
396 ref <- newIORef (throw NonTermination)
397 ans <- unsafeInterleaveIO (readIORef ref)
399 writeIORef ref result
402 -- NOTE: we do our own explicit black holing here, because GHC's lazy
403 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
404 -- computation a few times before it notices the loop, which is wrong.
408 -- Assume a unix platform, where text and binary I/O are identical.
409 openBinaryFile = openFile
410 hSetBinaryMode _ _ = return ()
413 -- | The function creates a temporary file in ReadWrite mode.
414 -- The created file isn\'t deleted automatically, so you need to delete it manually.
416 -- The file is creates with permissions such that only the current
417 -- user can read\/write it.
419 -- With some exceptions (see below), the file will be created securely
420 -- in the sense that an attacker should not be able to cause
421 -- openTempFile to overwrite another file on the filesystem using your
422 -- credentials, by putting symbolic links (on Unix) in the place where
423 -- the temporary file is to be created. On Unix the @O_CREAT@ and
424 -- @O_EXCL@ flags are used to prevent this attack, but note that
425 -- @O_EXCL@ is sometimes not supported on NFS filesystems, so if you
426 -- rely on this behaviour it is best to use local filesystems only.
428 openTempFile :: FilePath -- ^ Directory in which to create the file
429 -> String -- ^ File name template. If the template is \"foo.ext\" then
430 -- the created file will be \"fooXXX.ext\" where XXX is some
432 -> IO (FilePath, Handle)
433 openTempFile tmp_dir template = openTempFile' "openTempFile" tmp_dir template False
435 -- | Like 'openTempFile', but opens the file in binary mode. See 'openBinaryFile' for more comments.
436 openBinaryTempFile :: FilePath -> String -> IO (FilePath, Handle)
437 openBinaryTempFile tmp_dir template = openTempFile' "openBinaryTempFile" tmp_dir template True
439 openTempFile' :: String -> FilePath -> String -> Bool -> IO (FilePath, Handle)
440 openTempFile' loc tmp_dir template binary = do
444 -- We split off the last extension, so we can use .foo.ext files
445 -- for temporary files (hidden on Unix OSes). Unfortunately we're
446 -- below filepath in the hierarchy here.
448 case break (== '.') $ reverse template of
449 -- First case: template contains no '.'s. Just re-reverse it.
450 (rev_suffix, "") -> (reverse rev_suffix, "")
451 -- Second case: template contains at least one '.'. Strip the
452 -- dot from the prefix and prepend it to the suffix (if we don't
453 -- do this, the unique number will get added after the '.' and
454 -- thus be part of the extension, which is wrong.)
455 (rev_suffix, '.':rest) -> (reverse rest, '.':reverse rev_suffix)
456 -- Otherwise, something is wrong, because (break (== '.')) should
457 -- always return a pair with either the empty string or a string
458 -- beginning with '.' as the second component.
459 _ -> error "bug in System.IO.openTempFile"
462 oflags1 = rw_flags .|. o_EXCL
468 oflags = oflags1 .|. binary_flags
472 findTempName x = do h <- openFile filepath ReadWriteMode
476 fd <- withFilePath filepath $ \ f ->
477 c_open f oflags 0o600
482 then findTempName (x+1)
483 else ioError (errnoToIOError loc errno Nothing (Just tmp_dir))
485 -- XXX We want to tell fdToHandle what the filepath is,
486 -- as any exceptions etc will only be able to report the
488 h <- fdToHandle fd `onException` c_close fd
492 filename = prefix ++ show x ++ suffix
493 filepath = tmp_dir `combine` filename
495 -- XXX bits copied from System.FilePath, since that's not available here
499 | last a == pathSeparator = a ++ b
500 | otherwise = a ++ [pathSeparator] ++ b
503 fdToHandle fd = openFd (fromIntegral fd) False ReadWriteMode binary
506 -- XXX Should use filepath library
507 pathSeparator :: Char
508 #ifdef mingw32_HOST_OS
515 -- XXX Copied from GHC.Handle
516 std_flags, output_flags, rw_flags :: CInt
517 std_flags = o_NONBLOCK .|. o_NOCTTY
518 output_flags = std_flags .|. o_CREAT
519 rw_flags = output_flags .|. o_RDWR
523 foreign import ccall "getpid" c_getpid :: IO Int
527 -- Implementations should enforce as far as possible, at least locally to the
528 -- Haskell process, multiple-reader single-writer locking on files.
529 -- That is, /there may either be many handles on the same file which manage
530 -- input, or just one handle on the file which manages output/. If any
531 -- open or semi-closed handle is managing a file for output, no new
532 -- handle can be allocated for that file. If any open or semi-closed
533 -- handle is managing a file for input, new handles can only be allocated
534 -- if they do not manage output. Whether two files are the same is
535 -- implementation-dependent, but they should normally be the same if they
536 -- have the same absolute path name and neither has been renamed, for
539 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
540 -- the file until the entire contents of the file have been consumed.
541 -- It follows that an attempt to write to a file (using 'writeFile', for
542 -- example) that was earlier opened by 'readFile' will usually result in
543 -- failure with 'System.IO.Error.isAlreadyInUseError'.