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
163 #if !defined(__NHC__) && !defined(__HUGS__)
164 -- * Unicode encoding\/decoding
166 -- | A text-mode 'Handle' has an associated 'TextEncoding', which
167 -- is used to decode bytes into Unicode characters when reading,
168 -- and encode Unicode characters into bytes when writing.
170 -- The default 'TextEncoding' is the same as the default encoding
171 -- on your system, which is also available as 'localeEncoding'.
172 -- (GHC note: on Windows, currently 'localeEncoding' is always
173 -- 'latin1'; there is no support for encoding and decoding using
174 -- the ANSI code page).
176 -- Encoding and decoding errors are always detected and reported,
177 -- except during lazy I/O ('hGetContents', 'getContents', and
178 -- 'readFile'), where a decoding error merely results in
179 -- termination of the character stream, as with other I/O errors.
183 -- ** Unicode encodings
187 utf16, utf16le, utf16be,
188 utf32, utf32le, utf32be,
193 #if !defined(__NHC__) && !defined(__HUGS__)
194 -- * Newline conversion
196 -- | In Haskell, a newline is always represented by the character
197 -- '\n'. However, in files and external character streams, a
198 -- newline may be represented by another character sequence, such
201 -- A text-mode 'Handle' has an associated 'NewlineMode' that
202 -- specifies how to transate newline characters. The
203 -- 'NewlineMode' specifies the input and output translation
204 -- separately, so that for instance you can translate '\r\n'
205 -- to '\n' on input, but leave newlines as '\n' on output.
207 -- The default 'NewlineMode' for a 'Handle' is
208 -- 'nativeNewlineMode', which does no translation on Unix systems,
209 -- but translates '\r\n' to '\n' and back on Windows.
211 -- Binary-mode 'Handle's do no newline translation at all.
214 Newline(..), nativeNewline,
216 noNewlineTranslation, universalNewlineMode, nativeNewlineMode,
220 import Control.Exception.Base
226 import Foreign.C.Error
227 import Foreign.C.Types
228 import System.Posix.Internals
231 #ifdef __GLASGOW_HASKELL__
233 import GHC.IO hiding ( onException )
235 import GHC.IO.Handle.FD
238 import GHC.IO.Exception ( userError )
239 import GHC.IO.Encoding
250 import System.IO.Unsafe ( unsafeInterleaveIO )
257 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
258 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
259 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
260 , stdin, stdout, stderr
261 , openFile -- :: FilePath -> IOMode -> IO Handle
262 , hClose -- :: Handle -> IO ()
263 , hFileSize -- :: Handle -> IO Integer
264 , hIsEOF -- :: Handle -> IO Bool
265 , isEOF -- :: IO Bool
266 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
267 , hGetBuffering -- :: Handle -> IO BufferMode
268 , hFlush -- :: Handle -> IO ()
269 , hGetPosn -- :: Handle -> IO HandlePosn
270 , hSetPosn -- :: HandlePosn -> IO ()
271 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
272 , hWaitForInput -- :: Handle -> Int -> IO Bool
273 , hGetChar -- :: Handle -> IO Char
274 , hGetLine -- :: Handle -> IO [Char]
275 , hLookAhead -- :: Handle -> IO Char
276 , hGetContents -- :: Handle -> IO [Char]
277 , hPutChar -- :: Handle -> Char -> IO ()
278 , hPutStr -- :: Handle -> [Char] -> IO ()
279 , hPutStrLn -- :: Handle -> [Char] -> IO ()
280 , hPrint -- :: Handle -> [Char] -> IO ()
281 , hReady -- :: Handle -> [Char] -> IO ()
282 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
283 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
284 , hIsSeekable -- :: Handle -> IO Bool
288 , FilePath -- :: String
290 import NHC.IOExtras (fixIO, hPutBuf, hGetBuf)
294 -- -----------------------------------------------------------------------------
297 #ifdef __GLASGOW_HASKELL__
298 -- | Write a character to the standard output device
299 -- (same as 'hPutChar' 'stdout').
301 putChar :: Char -> IO ()
302 putChar c = hPutChar stdout c
304 -- | Write a string to the standard output device
305 -- (same as 'hPutStr' 'stdout').
307 putStr :: String -> IO ()
308 putStr s = hPutStr stdout s
310 -- | The same as 'putStr', but adds a newline character.
312 putStrLn :: String -> IO ()
313 putStrLn s = do putStr s
316 -- | The 'print' function outputs a value of any printable type to the
317 -- standard output device.
318 -- Printable types are those that are instances of class 'Show'; 'print'
319 -- converts values to strings for output using the 'show' operation and
322 -- For example, a program to print the first 20 integers and their
323 -- powers of 2 could be written as:
325 -- > main = print ([(n, 2^n) | n <- [0..19]])
327 print :: Show a => a -> IO ()
328 print x = putStrLn (show x)
330 -- | Read a character from the standard input device
331 -- (same as 'hGetChar' 'stdin').
334 getChar = hGetChar stdin
336 -- | Read a line from the standard input device
337 -- (same as 'hGetLine' 'stdin').
340 getLine = hGetLine stdin
342 -- | The 'getContents' operation returns all user input as a single string,
343 -- which is read lazily as it is needed
344 -- (same as 'hGetContents' 'stdin').
346 getContents :: IO String
347 getContents = hGetContents stdin
349 -- | The 'interact' function takes a function of type @String->String@
350 -- as its argument. The entire input from the standard input device is
351 -- passed to this function as its argument, and the resulting string is
352 -- output on the standard output device.
354 interact :: (String -> String) -> IO ()
355 interact f = do s <- getContents
358 -- | The 'readFile' function reads a file and
359 -- returns the contents of the file as a string.
360 -- The file is read lazily, on demand, as with 'getContents'.
362 readFile :: FilePath -> IO String
363 readFile name = openFile name ReadMode >>= hGetContents
365 -- | The computation 'writeFile' @file str@ function writes the string @str@,
366 -- to the file @file@.
367 writeFile :: FilePath -> String -> IO ()
368 writeFile f txt = withFile f WriteMode (\ hdl -> hPutStr hdl txt)
370 -- | The computation 'appendFile' @file str@ function appends the string @str@,
371 -- to the file @file@.
373 -- Note that 'writeFile' and 'appendFile' write a literal string
374 -- to a file. To write a value of any printable type, as with 'print',
375 -- use the 'show' function to convert the value to a string first.
377 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
379 appendFile :: FilePath -> String -> IO ()
380 appendFile f txt = withFile f AppendMode (\ hdl -> hPutStr hdl txt)
382 -- | The 'readLn' function combines 'getLine' and 'readIO'.
384 readLn :: Read a => IO a
385 readLn = do l <- getLine
389 -- | The 'readIO' function is similar to 'read' except that it signals
390 -- parse failure to the 'IO' monad instead of terminating the program.
392 readIO :: Read a => String -> IO a
393 readIO s = case (do { (x,t) <- reads s ;
397 [] -> ioError (userError "Prelude.readIO: no parse")
398 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
399 #endif /* __GLASGOW_HASKELL__ */
402 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
403 -- available for input from handle @hdl@.
405 -- This operation may fail with:
407 -- * 'System.IO.Error.isEOFError' if the end of file has been reached.
409 hReady :: Handle -> IO Bool
410 hReady h = hWaitForInput h 0
412 -- | The same as 'hPutStr', but adds a newline character.
414 hPutStrLn :: Handle -> String -> IO ()
415 hPutStrLn hndl str = do
419 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
420 -- given by the 'shows' function to the file or channel managed by @hdl@
421 -- and appends a newline.
423 -- This operation may fail with:
425 -- * 'System.IO.Error.isFullError' if the device is full; or
427 -- * 'System.IO.Error.isPermissionError' if another system resource limit would be exceeded.
429 hPrint :: Show a => Handle -> a -> IO ()
430 hPrint hdl = hPutStrLn hdl . show
431 #endif /* !__NHC__ */
433 -- | @'withFile' name mode act@ opens a file using 'openFile' and passes
434 -- the resulting handle to the computation @act@. The handle will be
435 -- closed on exit from 'withFile', whether by normal termination or by
436 -- raising an exception.
437 withFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
438 withFile name mode = bracket (openFile name mode) hClose
440 -- | @'withBinaryFile' name mode act@ opens a file using 'openBinaryFile'
441 -- and passes the resulting handle to the computation @act@. The handle
442 -- will be closed on exit from 'withBinaryFile', whether by normal
443 -- termination or by raising an exception.
444 withBinaryFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
445 withBinaryFile name mode = bracket (openBinaryFile name mode) hClose
447 -- ---------------------------------------------------------------------------
450 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
451 fixIO :: (a -> IO a) -> IO a
453 ref <- newIORef (throw NonTermination)
454 ans <- unsafeInterleaveIO (readIORef ref)
456 writeIORef ref result
459 -- NOTE: we do our own explicit black holing here, because GHC's lazy
460 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
461 -- computation a few times before it notices the loop, which is wrong.
465 -- Assume a unix platform, where text and binary I/O are identical.
466 openBinaryFile = openFile
467 hSetBinaryMode _ _ = return ()
470 -- | The function creates a temporary file in ReadWrite mode.
471 -- The created file isn\'t deleted automatically, so you need to delete it manually.
473 -- The file is creates with permissions such that only the current
474 -- user can read\/write it.
476 -- With some exceptions (see below), the file will be created securely
477 -- in the sense that an attacker should not be able to cause
478 -- openTempFile to overwrite another file on the filesystem using your
479 -- credentials, by putting symbolic links (on Unix) in the place where
480 -- the temporary file is to be created. On Unix the @O_CREAT@ and
481 -- @O_EXCL@ flags are used to prevent this attack, but note that
482 -- @O_EXCL@ is sometimes not supported on NFS filesystems, so if you
483 -- rely on this behaviour it is best to use local filesystems only.
485 openTempFile :: FilePath -- ^ Directory in which to create the file
486 -> String -- ^ File name template. If the template is \"foo.ext\" then
487 -- the created file will be \"fooXXX.ext\" where XXX is some
489 -> IO (FilePath, Handle)
490 openTempFile tmp_dir template = openTempFile' "openTempFile" tmp_dir template False
492 -- | Like 'openTempFile', but opens the file in binary mode. See 'openBinaryFile' for more comments.
493 openBinaryTempFile :: FilePath -> String -> IO (FilePath, Handle)
494 openBinaryTempFile tmp_dir template = openTempFile' "openBinaryTempFile" tmp_dir template True
496 openTempFile' :: String -> FilePath -> String -> Bool -> IO (FilePath, Handle)
497 openTempFile' loc tmp_dir template binary = do
501 -- We split off the last extension, so we can use .foo.ext files
502 -- for temporary files (hidden on Unix OSes). Unfortunately we're
503 -- below filepath in the hierarchy here.
505 case break (== '.') $ reverse template of
506 -- First case: template contains no '.'s. Just re-reverse it.
507 (rev_suffix, "") -> (reverse rev_suffix, "")
508 -- Second case: template contains at least one '.'. Strip the
509 -- dot from the prefix and prepend it to the suffix (if we don't
510 -- do this, the unique number will get added after the '.' and
511 -- thus be part of the extension, which is wrong.)
512 (rev_suffix, '.':rest) -> (reverse rest, '.':reverse rev_suffix)
513 -- Otherwise, something is wrong, because (break (== '.')) should
514 -- always return a pair with either the empty string or a string
515 -- beginning with '.' as the second component.
516 _ -> error "bug in System.IO.openTempFile"
519 oflags1 = rw_flags .|. o_EXCL
525 oflags = oflags1 .|. binary_flags
529 findTempName x = do h <- openFile filepath ReadWriteMode
533 fd <- withFilePath filepath $ \ f ->
534 c_open f oflags 0o600
539 then findTempName (x+1)
540 else ioError (errnoToIOError loc errno Nothing (Just tmp_dir))
542 -- XXX We want to tell fdToHandle what the filepath is,
543 -- as any exceptions etc will only be able to report the
545 h <- fdToHandle fd `onException` c_close fd
549 filename = prefix ++ show x ++ suffix
550 filepath = tmp_dir `combine` filename
552 -- XXX bits copied from System.FilePath, since that's not available here
556 | last a == pathSeparator = a ++ b
557 | otherwise = a ++ [pathSeparator] ++ b
560 fdToHandle fd = openFd (fromIntegral fd) False ReadWriteMode binary
563 -- XXX Should use filepath library
564 pathSeparator :: Char
565 #ifdef mingw32_HOST_OS
572 -- XXX Copied from GHC.Handle
573 std_flags, output_flags, rw_flags :: CInt
574 std_flags = o_NONBLOCK .|. o_NOCTTY
575 output_flags = std_flags .|. o_CREAT
576 rw_flags = output_flags .|. o_RDWR
580 foreign import ccall "getpid" c_getpid :: IO Int
584 -- Implementations should enforce as far as possible, at least locally to the
585 -- Haskell process, multiple-reader single-writer locking on files.
586 -- That is, /there may either be many handles on the same file which manage
587 -- input, or just one handle on the file which manages output/. If any
588 -- open or semi-closed handle is managing a file for output, no new
589 -- handle can be allocated for that file. If any open or semi-closed
590 -- handle is managing a file for input, new handles can only be allocated
591 -- if they do not manage output. Whether two files are the same is
592 -- implementation-dependent, but they should normally be the same if they
593 -- have the same absolute path name and neither has been renamed, for
596 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
597 -- the file until the entire contents of the file have been consumed.
598 -- It follows that an attempt to write to a file (using 'writeFile', for
599 -- example) that was earlier opened by 'readFile' will usually result in
600 -- failure with 'System.IO.Error.isAlreadyInUseError'.