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.
184 -- ** Unicode encodings
188 utf16, utf16le, utf16be,
189 utf32, utf32le, utf32be,
194 #if !defined(__NHC__) && !defined(__HUGS__)
195 -- * Newline conversion
197 -- | In Haskell, a newline is always represented by the character
198 -- '\n'. However, in files and external character streams, a
199 -- newline may be represented by another character sequence, such
202 -- A text-mode 'Handle' has an associated 'NewlineMode' that
203 -- specifies how to transate newline characters. The
204 -- 'NewlineMode' specifies the input and output translation
205 -- separately, so that for instance you can translate '\r\n'
206 -- to '\n' on input, but leave newlines as '\n' on output.
208 -- The default 'NewlineMode' for a 'Handle' is
209 -- 'nativeNewlineMode', which does no translation on Unix systems,
210 -- but translates '\r\n' to '\n' and back on Windows.
212 -- Binary-mode 'Handle's do no newline translation at all.
215 Newline(..), nativeNewline,
217 noNewlineTranslation, universalNewlineMode, nativeNewlineMode,
221 import Control.Exception.Base
227 import Foreign.C.Error
228 import Foreign.C.Types
229 import System.Posix.Internals
232 #ifdef __GLASGOW_HASKELL__
234 import GHC.IO hiding ( onException )
236 import GHC.IO.Handle.FD
239 import GHC.IO.Exception ( userError )
240 import GHC.IO.Encoding
251 import System.IO.Unsafe ( unsafeInterleaveIO )
258 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
259 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
260 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
261 , stdin, stdout, stderr
262 , openFile -- :: FilePath -> IOMode -> IO Handle
263 , hClose -- :: Handle -> IO ()
264 , hFileSize -- :: Handle -> IO Integer
265 , hIsEOF -- :: Handle -> IO Bool
266 , isEOF -- :: IO Bool
267 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
268 , hGetBuffering -- :: Handle -> IO BufferMode
269 , hFlush -- :: Handle -> IO ()
270 , hGetPosn -- :: Handle -> IO HandlePosn
271 , hSetPosn -- :: HandlePosn -> IO ()
272 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
273 , hWaitForInput -- :: Handle -> Int -> IO Bool
274 , hGetChar -- :: Handle -> IO Char
275 , hGetLine -- :: Handle -> IO [Char]
276 , hLookAhead -- :: Handle -> IO Char
277 , hGetContents -- :: Handle -> IO [Char]
278 , hPutChar -- :: Handle -> Char -> IO ()
279 , hPutStr -- :: Handle -> [Char] -> IO ()
280 , hPutStrLn -- :: Handle -> [Char] -> IO ()
281 , hPrint -- :: Handle -> [Char] -> IO ()
282 , hReady -- :: Handle -> [Char] -> IO ()
283 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
284 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
285 , hIsSeekable -- :: Handle -> IO Bool
289 , FilePath -- :: String
291 import NHC.IOExtras (fixIO, hPutBuf, hGetBuf)
295 -- -----------------------------------------------------------------------------
298 #ifdef __GLASGOW_HASKELL__
299 -- | Write a character to the standard output device
300 -- (same as 'hPutChar' 'stdout').
302 putChar :: Char -> IO ()
303 putChar c = hPutChar stdout c
305 -- | Write a string to the standard output device
306 -- (same as 'hPutStr' 'stdout').
308 putStr :: String -> IO ()
309 putStr s = hPutStr stdout s
311 -- | The same as 'putStr', but adds a newline character.
313 putStrLn :: String -> IO ()
314 putStrLn s = do putStr s
317 -- | The 'print' function outputs a value of any printable type to the
318 -- standard output device.
319 -- Printable types are those that are instances of class 'Show'; 'print'
320 -- converts values to strings for output using the 'show' operation and
323 -- For example, a program to print the first 20 integers and their
324 -- powers of 2 could be written as:
326 -- > main = print ([(n, 2^n) | n <- [0..19]])
328 print :: Show a => a -> IO ()
329 print x = putStrLn (show x)
331 -- | Read a character from the standard input device
332 -- (same as 'hGetChar' 'stdin').
335 getChar = hGetChar stdin
337 -- | Read a line from the standard input device
338 -- (same as 'hGetLine' 'stdin').
341 getLine = hGetLine stdin
343 -- | The 'getContents' operation returns all user input as a single string,
344 -- which is read lazily as it is needed
345 -- (same as 'hGetContents' 'stdin').
347 getContents :: IO String
348 getContents = hGetContents stdin
350 -- | The 'interact' function takes a function of type @String->String@
351 -- as its argument. The entire input from the standard input device is
352 -- passed to this function as its argument, and the resulting string is
353 -- output on the standard output device.
355 interact :: (String -> String) -> IO ()
356 interact f = do s <- getContents
359 -- | The 'readFile' function reads a file and
360 -- returns the contents of the file as a string.
361 -- The file is read lazily, on demand, as with 'getContents'.
363 readFile :: FilePath -> IO String
364 readFile name = openFile name ReadMode >>= hGetContents
366 -- | The computation 'writeFile' @file str@ function writes the string @str@,
367 -- to the file @file@.
368 writeFile :: FilePath -> String -> IO ()
369 writeFile f txt = withFile f WriteMode (\ hdl -> hPutStr hdl txt)
371 -- | The computation 'appendFile' @file str@ function appends the string @str@,
372 -- to the file @file@.
374 -- Note that 'writeFile' and 'appendFile' write a literal string
375 -- to a file. To write a value of any printable type, as with 'print',
376 -- use the 'show' function to convert the value to a string first.
378 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
380 appendFile :: FilePath -> String -> IO ()
381 appendFile f txt = withFile f AppendMode (\ hdl -> hPutStr hdl txt)
383 -- | The 'readLn' function combines 'getLine' and 'readIO'.
385 readLn :: Read a => IO a
386 readLn = do l <- getLine
390 -- | The 'readIO' function is similar to 'read' except that it signals
391 -- parse failure to the 'IO' monad instead of terminating the program.
393 readIO :: Read a => String -> IO a
394 readIO s = case (do { (x,t) <- reads s ;
398 [] -> ioError (userError "Prelude.readIO: no parse")
399 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
400 #endif /* __GLASGOW_HASKELL__ */
403 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
404 -- available for input from handle @hdl@.
406 -- This operation may fail with:
408 -- * 'System.IO.Error.isEOFError' if the end of file has been reached.
410 hReady :: Handle -> IO Bool
411 hReady h = hWaitForInput h 0
413 -- | The same as 'hPutStr', but adds a newline character.
415 hPutStrLn :: Handle -> String -> IO ()
416 hPutStrLn hndl str = do
420 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
421 -- given by the 'shows' function to the file or channel managed by @hdl@
422 -- and appends a newline.
424 -- This operation may fail with:
426 -- * 'System.IO.Error.isFullError' if the device is full; or
428 -- * 'System.IO.Error.isPermissionError' if another system resource limit would be exceeded.
430 hPrint :: Show a => Handle -> a -> IO ()
431 hPrint hdl = hPutStrLn hdl . show
432 #endif /* !__NHC__ */
434 -- | @'withFile' name mode act@ opens a file using 'openFile' and passes
435 -- the resulting handle to the computation @act@. The handle will be
436 -- closed on exit from 'withFile', whether by normal termination or by
437 -- raising an exception.
438 withFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
439 withFile name mode = bracket (openFile name mode) hClose
441 -- | @'withBinaryFile' name mode act@ opens a file using 'openBinaryFile'
442 -- and passes the resulting handle to the computation @act@. The handle
443 -- will be closed on exit from 'withBinaryFile', whether by normal
444 -- termination or by raising an exception.
445 withBinaryFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
446 withBinaryFile name mode = bracket (openBinaryFile name mode) hClose
448 -- ---------------------------------------------------------------------------
451 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
452 fixIO :: (a -> IO a) -> IO a
454 ref <- newIORef (throw NonTermination)
455 ans <- unsafeInterleaveIO (readIORef ref)
457 writeIORef ref result
460 -- NOTE: we do our own explicit black holing here, because GHC's lazy
461 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
462 -- computation a few times before it notices the loop, which is wrong.
466 -- Assume a unix platform, where text and binary I/O are identical.
467 openBinaryFile = openFile
468 hSetBinaryMode _ _ = return ()
471 -- | The function creates a temporary file in ReadWrite mode.
472 -- The created file isn\'t deleted automatically, so you need to delete it manually.
474 -- The file is creates with permissions such that only the current
475 -- user can read\/write it.
477 -- With some exceptions (see below), the file will be created securely
478 -- in the sense that an attacker should not be able to cause
479 -- openTempFile to overwrite another file on the filesystem using your
480 -- credentials, by putting symbolic links (on Unix) in the place where
481 -- the temporary file is to be created. On Unix the @O_CREAT@ and
482 -- @O_EXCL@ flags are used to prevent this attack, but note that
483 -- @O_EXCL@ is sometimes not supported on NFS filesystems, so if you
484 -- rely on this behaviour it is best to use local filesystems only.
486 openTempFile :: FilePath -- ^ Directory in which to create the file
487 -> String -- ^ File name template. If the template is \"foo.ext\" then
488 -- the created file will be \"fooXXX.ext\" where XXX is some
490 -> IO (FilePath, Handle)
491 openTempFile tmp_dir template = openTempFile' "openTempFile" tmp_dir template False
493 -- | Like 'openTempFile', but opens the file in binary mode. See 'openBinaryFile' for more comments.
494 openBinaryTempFile :: FilePath -> String -> IO (FilePath, Handle)
495 openBinaryTempFile tmp_dir template = openTempFile' "openBinaryTempFile" tmp_dir template True
497 openTempFile' :: String -> FilePath -> String -> Bool -> IO (FilePath, Handle)
498 openTempFile' loc tmp_dir template binary = do
502 -- We split off the last extension, so we can use .foo.ext files
503 -- for temporary files (hidden on Unix OSes). Unfortunately we're
504 -- below filepath in the hierarchy here.
506 case break (== '.') $ reverse template of
507 -- First case: template contains no '.'s. Just re-reverse it.
508 (rev_suffix, "") -> (reverse rev_suffix, "")
509 -- Second case: template contains at least one '.'. Strip the
510 -- dot from the prefix and prepend it to the suffix (if we don't
511 -- do this, the unique number will get added after the '.' and
512 -- thus be part of the extension, which is wrong.)
513 (rev_suffix, '.':rest) -> (reverse rest, '.':reverse rev_suffix)
514 -- Otherwise, something is wrong, because (break (== '.')) should
515 -- always return a pair with either the empty string or a string
516 -- beginning with '.' as the second component.
517 _ -> error "bug in System.IO.openTempFile"
520 oflags1 = rw_flags .|. o_EXCL
526 oflags = oflags1 .|. binary_flags
530 findTempName x = do h <- openFile filepath ReadWriteMode
534 fd <- withFilePath filepath $ \ f ->
535 c_open f oflags 0o600
540 then findTempName (x+1)
541 else ioError (errnoToIOError loc errno Nothing (Just tmp_dir))
543 -- XXX We want to tell fdToHandle what the filepath is,
544 -- as any exceptions etc will only be able to report the
546 h <- fdToHandle fd `onException` c_close fd
550 filename = prefix ++ show x ++ suffix
551 filepath = tmp_dir `combine` filename
553 -- XXX bits copied from System.FilePath, since that's not available here
557 | last a == pathSeparator = a ++ b
558 | otherwise = a ++ [pathSeparator] ++ b
561 fdToHandle fd = openFd (fromIntegral fd) False ReadWriteMode binary
564 -- XXX Should use filepath library
565 pathSeparator :: Char
566 #ifdef mingw32_HOST_OS
573 -- XXX Copied from GHC.Handle
574 std_flags, output_flags, rw_flags :: CInt
575 std_flags = o_NONBLOCK .|. o_NOCTTY
576 output_flags = std_flags .|. o_CREAT
577 rw_flags = output_flags .|. o_RDWR
581 foreign import ccall "getpid" c_getpid :: IO Int
585 -- Implementations should enforce as far as possible, at least locally to the
586 -- Haskell process, multiple-reader single-writer locking on files.
587 -- That is, /there may either be many handles on the same file which manage
588 -- input, or just one handle on the file which manages output/. If any
589 -- open or semi-closed handle is managing a file for output, no new
590 -- handle can be allocated for that file. If any open or semi-closed
591 -- handle is managing a file for input, new handles can only be allocated
592 -- if they do not manage output. Whether two files are the same is
593 -- implementation-dependent, but they should normally be the same if they
594 -- have the same absolute path name and neither has been renamed, for
597 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
598 -- the file until the entire contents of the file have been consumed.
599 -- It follows that an attempt to write to a file (using 'writeFile', for
600 -- example) that was earlier opened by 'readFile' will usually result in
601 -- failure with 'System.IO.Error.isAlreadyInUseError'.