[project @ 2003-08-04 10:05:32 by ross]
[packages/random.git] / System / IO.hs
1 {-# OPTIONS -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
3 -- |
4 -- Module : System.IO
5 -- Copyright : (c) The University of Glasgow 2001
6 -- License : BSD-style (see the file libraries/base/LICENSE)
7 --
8 -- Maintainer : libraries@haskell.org
9 -- Stability : provisional
10 -- Portability : portable
11 --
12 -- The standard IO library.
13 --
14 -----------------------------------------------------------------------------
15
16 module System.IO (
17 -- * The IO monad
18
19 IO, -- instance MonadFix
20 fixIO, -- :: (a -> IO a) -> IO a
21
22 -- * Files and handles
23
24 FilePath, -- :: String
25
26 Handle, -- abstract, instance of: Eq, Show.
27
28 -- ** Standard handles
29
30 -- | Three handles are allocated during program initialisation,
31 -- and are initially open.
32
33 stdin, stdout, stderr, -- :: Handle
34
35 -- * Opening and closing files
36
37 -- ** Opening files
38
39 openFile, -- :: FilePath -> IOMode -> IO Handle
40 IOMode(ReadMode,WriteMode,AppendMode,ReadWriteMode),
41
42 -- ** Closing files
43
44 hClose, -- :: Handle -> IO ()
45
46 -- ** Special cases
47
48 -- | These functions are also exported by the "Prelude".
49
50 readFile, -- :: FilePath -> IO String
51 writeFile, -- :: FilePath -> String -> IO ()
52 appendFile, -- :: FilePath -> String -> IO ()
53
54 -- ** File locking
55
56 -- $locking
57
58 -- * Operations on handles
59
60 -- ** Determining the size of a file
61
62 hFileSize, -- :: Handle -> IO Integer
63
64 -- ** Detecting the end of input
65
66 hIsEOF, -- :: Handle -> IO Bool
67 isEOF, -- :: IO Bool
68
69 -- ** Buffering operations
70
71 BufferMode(NoBuffering,LineBuffering,BlockBuffering),
72 hSetBuffering, -- :: Handle -> BufferMode -> IO ()
73 hGetBuffering, -- :: Handle -> IO BufferMode
74 hFlush, -- :: Handle -> IO ()
75
76 -- ** Repositioning handles
77
78 hGetPosn, -- :: Handle -> IO HandlePosn
79 hSetPosn, -- :: HandlePosn -> IO ()
80 HandlePosn, -- abstract, instance of: Eq, Show.
81
82 hSeek, -- :: Handle -> SeekMode -> Integer -> IO ()
83 SeekMode(AbsoluteSeek,RelativeSeek,SeekFromEnd),
84 #if !defined(__NHC__)
85 hTell, -- :: Handle -> IO Integer
86 #endif
87
88 -- ** Handle properties
89
90 hIsOpen, hIsClosed, -- :: Handle -> IO Bool
91 hIsReadable, hIsWritable, -- :: Handle -> IO Bool
92 hIsSeekable, -- :: Handle -> IO Bool
93
94 -- ** Terminal operations
95
96 #if !defined(__HUGS__) && !defined(__NHC__)
97 hIsTerminalDevice, -- :: Handle -> IO Bool
98
99 hSetEcho, -- :: Handle -> Bool -> IO ()
100 hGetEcho, -- :: Handle -> IO Bool
101 #endif
102
103 -- ** Showing handle state
104
105 #ifdef __GLASGOW_HASKELL__
106 hShow, -- :: Handle -> IO String
107 #endif
108
109 -- * Text input and output
110
111 -- ** Text input
112
113 hWaitForInput, -- :: Handle -> Int -> IO Bool
114 hReady, -- :: Handle -> IO Bool
115 hGetChar, -- :: Handle -> IO Char
116 hGetLine, -- :: Handle -> IO [Char]
117 hLookAhead, -- :: Handle -> IO Char
118 hGetContents, -- :: Handle -> IO [Char]
119
120 -- ** Text output
121
122 hPutChar, -- :: Handle -> Char -> IO ()
123 hPutStr, -- :: Handle -> [Char] -> IO ()
124 hPutStrLn, -- :: Handle -> [Char] -> IO ()
125 hPrint, -- :: Show a => Handle -> a -> IO ()
126
127 -- ** Special cases for standard input and output
128
129 -- | These functions are also exported by the "Prelude".
130
131 interact, -- :: (String -> String) -> IO ()
132 putChar, -- :: Char -> IO ()
133 putStr, -- :: String -> IO ()
134 putStrLn, -- :: String -> IO ()
135 print, -- :: Show a => a -> IO ()
136 getChar, -- :: IO Char
137 getLine, -- :: IO String
138 getContents, -- :: IO String
139 readIO, -- :: Read a => String -> IO a
140 readLn, -- :: Read a => IO a
141
142 -- * Binary input and output
143
144 #if !defined(__NHC__)
145 openBinaryFile, -- :: FilePath -> IOMode -> IO Handle
146 #endif
147
148 #if !defined(__HUGS__) && !defined(__NHC__)
149 hSetBinaryMode, -- :: Handle -> Bool -> IO ()
150 hPutBuf, -- :: Handle -> Ptr a -> Int -> IO ()
151 hGetBuf, -- :: Handle -> Ptr a -> Int -> IO Int
152 #endif
153
154 module System.IO.Error,
155 ) where
156
157 #ifdef __GLASGOW_HASKELL__
158 import GHC.Base
159 import GHC.IOBase -- Together these four Prelude modules define
160 import GHC.Handle -- all the stuff exported by IO for the GHC version
161 import GHC.IO
162 import GHC.ST ( fixST )
163 import GHC.Exception
164 import GHC.Num
165 import GHC.Read
166 import GHC.Show
167 #endif
168
169 #ifdef __HUGS__
170 import Hugs.IO
171 import Hugs.IOExts
172 #endif
173
174 #ifdef __NHC__
175 import IO
176 ( Handle ()
177 , HandlePosn ()
178 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
179 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
180 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
181 , stdin, stdout, stderr
182 , openFile -- :: FilePath -> IOMode -> IO Handle
183 , hClose -- :: Handle -> IO ()
184 , hFileSize -- :: Handle -> IO Integer
185 , hIsEOF -- :: Handle -> IO Bool
186 , isEOF -- :: IO Bool
187 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
188 , hGetBuffering -- :: Handle -> IO BufferMode
189 , hFlush -- :: Handle -> IO ()
190 , hGetPosn -- :: Handle -> IO HandlePosn
191 , hSetPosn -- :: HandlePosn -> IO ()
192 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
193 , hWaitForInput -- :: Handle -> Int -> IO Bool
194 , hGetChar -- :: Handle -> IO Char
195 , hGetLine -- :: Handle -> IO [Char]
196 , hLookAhead -- :: Handle -> IO Char
197 , hGetContents -- :: Handle -> IO [Char]
198 , hPutChar -- :: Handle -> Char -> IO ()
199 , hPutStr -- :: Handle -> [Char] -> IO ()
200 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
201 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
202 , hIsSeekable -- :: Handle -> IO Bool
203
204 , IO ()
205 , FilePath -- :: String
206 )
207 import NHC.Internal (unsafePerformIO)
208 #endif
209
210 import System.IO.Error (
211 isAlreadyExistsError, isDoesNotExistError, -- :: IOError -> Bool
212 isAlreadyInUseError, isFullError,
213 isEOFError, isIllegalOperation,
214 isPermissionError, isUserError,
215
216 ioeGetErrorString, -- :: IOError -> String
217 ioeGetHandle, -- :: IOError -> Maybe Handle
218 ioeGetFileName, -- :: IOError -> Maybe FilePath
219
220 try, -- :: IO a -> IO (Either IOError a)
221
222 -- re-exports of Prelude names
223 IOError,
224 ioError, -- :: IOError -> IO a
225 userError, -- :: String -> IOError
226 catch -- :: IO a -> (IOError -> IO a) -> IO a
227 )
228
229 -- -----------------------------------------------------------------------------
230 -- Standard IO
231
232 #ifndef __HUGS__
233 -- | Write a character to the standard output device
234 -- (same as 'hPutChar' 'stdout').
235
236 putChar :: Char -> IO ()
237 putChar c = hPutChar stdout c
238
239 -- | Write a string to the standard output device
240 -- (same as 'hPutStr' 'stdout').
241
242 putStr :: String -> IO ()
243 putStr s = hPutStr stdout s
244
245 -- | The same as 'putStrLn', but adds a newline character.
246
247 putStrLn :: String -> IO ()
248 putStrLn s = do putStr s
249 putChar '\n'
250
251 -- | The 'print' function outputs a value of any printable type to the
252 -- standard output device.
253 -- Printable types are those that are instances of class 'Show'; 'print'
254 -- converts values to strings for output using the 'show' operation and
255 -- adds a newline.
256 --
257 -- For example, a program to print the first 20 integers and their
258 -- powers of 2 could be written as:
259 --
260 -- > main = print ([(n, 2^n) | n <- [0..19]])
261
262 print :: Show a => a -> IO ()
263 print x = putStrLn (show x)
264
265 -- | Read a character from the standard input device
266 -- (same as 'hGetChar' 'stdin').
267
268 getChar :: IO Char
269 getChar = hGetChar stdin
270
271 -- | Read a line from the standard input device
272 -- (same as 'hGetLine' 'stdin').
273
274 getLine :: IO String
275 getLine = hGetLine stdin
276
277 -- | The 'getContents' operation returns all user input as a single string,
278 -- which is read lazily as it is needed
279 -- (same as 'hGetContents' 'stdin').
280
281 getContents :: IO String
282 getContents = hGetContents stdin
283
284 -- | The 'interact' function takes a function of type @String->String@
285 -- as its argument. The entire input from the standard input device is
286 -- passed to this function as its argument, and the resulting string is
287 -- output on the standard output device.
288
289 interact :: (String -> String) -> IO ()
290 interact f = do s <- getContents
291 putStr (f s)
292
293 -- | The 'readFile' function reads a file and
294 -- returns the contents of the file as a string.
295 -- The file is read lazily, on demand, as with 'getContents'.
296
297 readFile :: FilePath -> IO String
298 readFile name = openFile name ReadMode >>= hGetContents
299
300 -- | The computation 'writeFile' @file str@ function writes the string @str@,
301 -- to the file @file@.
302
303 writeFile :: FilePath -> String -> IO ()
304 writeFile name str = do
305 hdl <- openFile name WriteMode
306 hPutStr hdl str
307 hClose hdl
308
309 -- | The computation 'appendFile' @file str@ function appends the string @str@,
310 -- to the file @file@.
311 --
312 -- Note that 'writeFile' and 'appendFile' write a literal string
313 -- to a file. To write a value of any printable type, as with 'print',
314 -- use the 'show' function to convert the value to a string first.
315 --
316 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
317
318 appendFile :: FilePath -> String -> IO ()
319 appendFile name str = do
320 hdl <- openFile name AppendMode
321 hPutStr hdl str
322 hClose hdl
323
324 -- | The 'readLn' function combines 'getLine' and 'readIO'.
325
326 readLn :: Read a => IO a
327 readLn = do l <- getLine
328 r <- readIO l
329 return r
330
331 -- | The 'readIO' function is similar to 'read' except that it signals
332 -- parse failure to the 'IO' monad instead of terminating the program.
333
334 readIO :: Read a => String -> IO a
335 readIO s = case (do { (x,t) <- reads s ;
336 ("","") <- lex t ;
337 return x }) of
338 [x] -> return x
339 [] -> ioError (userError "Prelude.readIO: no parse")
340 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
341 #endif /* __HUGS__ */
342
343 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
344 -- available for input from handle "hdl".
345 --
346 -- This operation may fail with:
347 --
348 -- * 'isEOFError' if the end of file has been reached.
349
350 hReady :: Handle -> IO Bool
351 hReady h = hWaitForInput h 0
352
353 -- | The same as 'hPutStr', but adds a newline character.
354
355 hPutStrLn :: Handle -> String -> IO ()
356 hPutStrLn hndl str = do
357 hPutStr hndl str
358 hPutChar hndl '\n'
359
360 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
361 -- given by the 'shows' function to the file or channel managed by @hdl@
362 -- and appends a newline.
363 --
364 -- This operation may fail with:
365 --
366 -- * 'isFullError' if the device is full; or
367 --
368 -- * 'isPermissionError' if another system resource limit would be exceeded.
369
370 hPrint :: Show a => Handle -> a -> IO ()
371 hPrint hdl = hPutStrLn hdl . show
372
373 -- ---------------------------------------------------------------------------
374 -- fixIO
375
376 #ifdef __GLASGOW_HASKELL__
377 fixIO :: (a -> IO a) -> IO a
378 fixIO m = stToIO (fixST (ioToST . m))
379 #endif
380 #ifdef __NHC__
381 fixIO :: (a -> IO a) -> IO a
382 fixIO f = let x = unsafePerformIO (f x) in return x
383 #endif
384
385 -- $locking
386 -- Implementations should enforce as far as possible, at least locally to the
387 -- Haskell process, multiple-reader single-writer locking on files.
388 -- That is, /there may either be many handles on the same file which manage
389 -- input, or just one handle on the file which manages output/. If any
390 -- open or semi-closed handle is managing a file for output, no new
391 -- handle can be allocated for that file. If any open or semi-closed
392 -- handle is managing a file for input, new handles can only be allocated
393 -- if they do not manage output. Whether two files are the same is
394 -- implementation-dependent, but they should normally be the same if they
395 -- have the same absolute path name and neither has been renamed, for
396 -- example.
397 --
398 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
399 -- the file until the entire contents of the file have been consumed.
400 -- It follows that an attempt to write to a file (using 'writeFile', for
401 -- example) that was earlier opened by 'readFile' will usually result in
402 -- failure with 'isAlreadyInUseError'.