a7552f5626ee9afc44e8102ad9fff60e814fbff9
[packages/old-time.git] / System / IO.hs
1 {-# OPTIONS_GHC -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 : stable
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 withFile,
40 openFile, -- :: FilePath -> IOMode -> IO Handle
41 IOMode(ReadMode,WriteMode,AppendMode,ReadWriteMode),
42
43 -- ** Closing files
44
45 hClose, -- :: Handle -> IO ()
46
47 -- ** Special cases
48
49 -- | These functions are also exported by the "Prelude".
50
51 readFile, -- :: FilePath -> IO String
52 writeFile, -- :: FilePath -> String -> IO ()
53 appendFile, -- :: FilePath -> String -> IO ()
54
55 -- ** File locking
56
57 -- $locking
58
59 -- * Operations on handles
60
61 -- ** Determining and changing the size of a file
62
63 hFileSize, -- :: Handle -> IO Integer
64 #ifdef __GLASGOW_HASKELL__
65 hSetFileSize, -- :: Handle -> Integer -> IO ()
66 #endif
67
68 -- ** Detecting the end of input
69
70 hIsEOF, -- :: Handle -> IO Bool
71 isEOF, -- :: IO Bool
72
73 -- ** Buffering operations
74
75 BufferMode(NoBuffering,LineBuffering,BlockBuffering),
76 hSetBuffering, -- :: Handle -> BufferMode -> IO ()
77 hGetBuffering, -- :: Handle -> IO BufferMode
78 hFlush, -- :: Handle -> IO ()
79
80 -- ** Repositioning handles
81
82 hGetPosn, -- :: Handle -> IO HandlePosn
83 hSetPosn, -- :: HandlePosn -> IO ()
84 HandlePosn, -- abstract, instance of: Eq, Show.
85
86 hSeek, -- :: Handle -> SeekMode -> Integer -> IO ()
87 SeekMode(AbsoluteSeek,RelativeSeek,SeekFromEnd),
88 #if !defined(__NHC__)
89 hTell, -- :: Handle -> IO Integer
90 #endif
91
92 -- ** Handle properties
93
94 hIsOpen, hIsClosed, -- :: Handle -> IO Bool
95 hIsReadable, hIsWritable, -- :: Handle -> IO Bool
96 hIsSeekable, -- :: Handle -> IO Bool
97
98 -- ** Terminal operations
99
100 #if !defined(__NHC__)
101 hIsTerminalDevice, -- :: Handle -> IO Bool
102
103 hSetEcho, -- :: Handle -> Bool -> IO ()
104 hGetEcho, -- :: Handle -> IO Bool
105 #endif
106
107 -- ** Showing handle state
108
109 #ifdef __GLASGOW_HASKELL__
110 hShow, -- :: Handle -> IO String
111 #endif
112
113 -- * Text input and output
114
115 -- ** Text input
116
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]
123
124 -- ** Text output
125
126 hPutChar, -- :: Handle -> Char -> IO ()
127 hPutStr, -- :: Handle -> [Char] -> IO ()
128 hPutStrLn, -- :: Handle -> [Char] -> IO ()
129 hPrint, -- :: Show a => Handle -> a -> IO ()
130
131 -- ** Special cases for standard input and output
132
133 -- | These functions are also exported by the "Prelude".
134
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
145
146 -- * Binary input and output
147
148 withBinaryFile,
149 openBinaryFile, -- :: FilePath -> IOMode -> IO Handle
150 hSetBinaryMode, -- :: Handle -> Bool -> IO ()
151 #if !defined(__NHC__)
152 hPutBuf, -- :: Handle -> Ptr a -> Int -> IO ()
153 hGetBuf, -- :: Handle -> Ptr a -> Int -> IO Int
154 #endif
155 #if !defined(__NHC__) && !defined(__HUGS__)
156 hPutBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
157 hGetBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
158 #endif
159
160 -- * Temporary files
161
162 #ifdef __GLASGOW_HASKELL__
163 openTempFile,
164 openBinaryTempFile,
165 #endif
166 ) where
167
168 #ifdef __GLASGOW_HASKELL__
169 import GHC.Base
170 import GHC.IOBase -- Together these four Prelude modules define
171 import GHC.Handle -- all the stuff exported by IO for the GHC version
172 import GHC.IO
173 import GHC.Exception
174 import GHC.Num
175 import GHC.Read
176 import GHC.Show
177 #endif
178
179 #ifdef __HUGS__
180 import Hugs.IO
181 import Hugs.IOExts
182 import Hugs.IORef
183 import Hugs.Prelude ( throw, Exception(NonTermination) )
184 import Control.Exception ( bracket )
185 import System.IO.Unsafe ( unsafeInterleaveIO )
186 #endif
187
188 #ifdef __NHC__
189 import IO
190 ( Handle ()
191 , HandlePosn ()
192 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
193 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
194 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
195 , stdin, stdout, stderr
196 , openFile -- :: FilePath -> IOMode -> IO Handle
197 , hClose -- :: Handle -> IO ()
198 , hFileSize -- :: Handle -> IO Integer
199 , hIsEOF -- :: Handle -> IO Bool
200 , isEOF -- :: IO Bool
201 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
202 , hGetBuffering -- :: Handle -> IO BufferMode
203 , hFlush -- :: Handle -> IO ()
204 , hGetPosn -- :: Handle -> IO HandlePosn
205 , hSetPosn -- :: HandlePosn -> IO ()
206 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
207 , hWaitForInput -- :: Handle -> Int -> IO Bool
208 , hGetChar -- :: Handle -> IO Char
209 , hGetLine -- :: Handle -> IO [Char]
210 , hLookAhead -- :: Handle -> IO Char
211 , hGetContents -- :: Handle -> IO [Char]
212 , hPutChar -- :: Handle -> Char -> IO ()
213 , hPutStr -- :: Handle -> [Char] -> IO ()
214 , hPutStrLn -- :: Handle -> [Char] -> IO ()
215 , hPrint -- :: Handle -> [Char] -> IO ()
216 , hReady -- :: Handle -> [Char] -> IO ()
217 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
218 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
219 , hIsSeekable -- :: Handle -> IO Bool
220 , bracket
221
222 , IO ()
223 , FilePath -- :: String
224 )
225 import NHC.IOExtras (fixIO)
226 #endif
227
228 -- -----------------------------------------------------------------------------
229 -- Standard IO
230
231 #ifdef __GLASGOW_HASKELL__
232 -- | Write a character to the standard output device
233 -- (same as 'hPutChar' 'stdout').
234
235 putChar :: Char -> IO ()
236 putChar c = hPutChar stdout c
237
238 -- | Write a string to the standard output device
239 -- (same as 'hPutStr' 'stdout').
240
241 putStr :: String -> IO ()
242 putStr s = hPutStr stdout s
243
244 -- | The same as 'putStr', but adds a newline character.
245
246 putStrLn :: String -> IO ()
247 putStrLn s = do putStr s
248 putChar '\n'
249
250 -- | The 'print' function outputs a value of any printable type to the
251 -- standard output device.
252 -- Printable types are those that are instances of class 'Show'; 'print'
253 -- converts values to strings for output using the 'show' operation and
254 -- adds a newline.
255 --
256 -- For example, a program to print the first 20 integers and their
257 -- powers of 2 could be written as:
258 --
259 -- > main = print ([(n, 2^n) | n <- [0..19]])
260
261 print :: Show a => a -> IO ()
262 print x = putStrLn (show x)
263
264 -- | Read a character from the standard input device
265 -- (same as 'hGetChar' 'stdin').
266
267 getChar :: IO Char
268 getChar = hGetChar stdin
269
270 -- | Read a line from the standard input device
271 -- (same as 'hGetLine' 'stdin').
272
273 getLine :: IO String
274 getLine = hGetLine stdin
275
276 -- | The 'getContents' operation returns all user input as a single string,
277 -- which is read lazily as it is needed
278 -- (same as 'hGetContents' 'stdin').
279
280 getContents :: IO String
281 getContents = hGetContents stdin
282
283 -- | The 'interact' function takes a function of type @String->String@
284 -- as its argument. The entire input from the standard input device is
285 -- passed to this function as its argument, and the resulting string is
286 -- output on the standard output device.
287
288 interact :: (String -> String) -> IO ()
289 interact f = do s <- getContents
290 putStr (f s)
291
292 -- | The 'readFile' function reads a file and
293 -- returns the contents of the file as a string.
294 -- The file is read lazily, on demand, as with 'getContents'.
295
296 readFile :: FilePath -> IO String
297 readFile name = openFile name ReadMode >>= hGetContents
298
299 -- | The computation 'writeFile' @file str@ function writes the string @str@,
300 -- to the file @file@.
301 writeFile :: FilePath -> String -> IO ()
302 writeFile f txt = bracket (openFile f WriteMode) hClose
303 (\hdl -> hPutStr hdl txt)
304
305 -- | The computation 'appendFile' @file str@ function appends the string @str@,
306 -- to the file @file@.
307 --
308 -- Note that 'writeFile' and 'appendFile' write a literal string
309 -- to a file. To write a value of any printable type, as with 'print',
310 -- use the 'show' function to convert the value to a string first.
311 --
312 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
313
314 appendFile :: FilePath -> String -> IO ()
315 appendFile f txt = bracket (openFile f AppendMode) hClose
316 (\hdl -> hPutStr hdl txt)
317
318 -- | The 'readLn' function combines 'getLine' and 'readIO'.
319
320 readLn :: Read a => IO a
321 readLn = do l <- getLine
322 r <- readIO l
323 return r
324
325 -- | The 'readIO' function is similar to 'read' except that it signals
326 -- parse failure to the 'IO' monad instead of terminating the program.
327
328 readIO :: Read a => String -> IO a
329 readIO s = case (do { (x,t) <- reads s ;
330 ("","") <- lex t ;
331 return x }) of
332 [x] -> return x
333 [] -> ioError (userError "Prelude.readIO: no parse")
334 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
335 #endif /* __GLASGOW_HASKELL__ */
336
337 #ifndef __NHC__
338 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
339 -- available for input from handle @hdl@.
340 --
341 -- This operation may fail with:
342 --
343 -- * 'System.IO.Error.isEOFError' if the end of file has been reached.
344
345 hReady :: Handle -> IO Bool
346 hReady h = hWaitForInput h 0
347
348 -- | The same as 'hPutStr', but adds a newline character.
349
350 hPutStrLn :: Handle -> String -> IO ()
351 hPutStrLn hndl str = do
352 hPutStr hndl str
353 hPutChar hndl '\n'
354
355 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
356 -- given by the 'shows' function to the file or channel managed by @hdl@
357 -- and appends a newline.
358 --
359 -- This operation may fail with:
360 --
361 -- * 'System.IO.Error.isFullError' if the device is full; or
362 --
363 -- * 'System.IO.Error.isPermissionError' if another system resource limit would be exceeded.
364
365 hPrint :: Show a => Handle -> a -> IO ()
366 hPrint hdl = hPutStrLn hdl . show
367 #endif /* !__NHC__ */
368
369 -- | @'withFile' name mode act@ opens a file using 'openFile' and passes
370 -- the resulting handle to the computation @act@. The handle will be
371 -- closed on exit from 'withFile', whether by normal termination or by
372 -- raising an exception.
373 withFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
374 withFile name mode = bracket (openFile name mode) hClose
375
376 -- | @'withBinaryFile' name mode act@ opens a file using 'openBinaryFile'
377 -- and passes the resulting handle to the computation @act@. The handle
378 -- will be closed on exit from 'withBinaryFile', whether by normal
379 -- termination or by raising an exception.
380 withBinaryFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
381 withBinaryFile name mode = bracket (openBinaryFile name mode) hClose
382
383 -- ---------------------------------------------------------------------------
384 -- fixIO
385
386 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
387 fixIO :: (a -> IO a) -> IO a
388 fixIO k = do
389 ref <- newIORef (throw NonTermination)
390 ans <- unsafeInterleaveIO (readIORef ref)
391 result <- k ans
392 writeIORef ref result
393 return result
394
395 -- NOTE: we do our own explicit black holing here, because GHC's lazy
396 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
397 -- computation a few times before it notices the loop, which is wrong.
398 #endif
399
400 #if defined(__NHC__)
401 -- Assume a unix platform, where text and binary I/O are identical.
402 openBinaryFile = openFile
403 hSetBinaryMode _ _ = return ()
404 #endif
405
406 -- $locking
407 -- Implementations should enforce as far as possible, at least locally to the
408 -- Haskell process, multiple-reader single-writer locking on files.
409 -- That is, /there may either be many handles on the same file which manage
410 -- input, or just one handle on the file which manages output/. If any
411 -- open or semi-closed handle is managing a file for output, no new
412 -- handle can be allocated for that file. If any open or semi-closed
413 -- handle is managing a file for input, new handles can only be allocated
414 -- if they do not manage output. Whether two files are the same is
415 -- implementation-dependent, but they should normally be the same if they
416 -- have the same absolute path name and neither has been renamed, for
417 -- example.
418 --
419 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
420 -- the file until the entire contents of the file have been consumed.
421 -- It follows that an attempt to write to a file (using 'writeFile', for
422 -- example) that was earlier opened by 'readFile' will usually result in
423 -- failure with 'System.IO.Error.isAlreadyInUseError'.
424
425 -- -----------------------------------------------------------------------------
426 -- Utils
427
428 #ifdef __GLASGOW_HASKELL__
429 -- Copied here to avoid recursive dependency with Control.Exception
430 bracket
431 :: IO a -- ^ computation to run first (\"acquire resource\")
432 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
433 -> (a -> IO c) -- ^ computation to run in-between
434 -> IO c -- returns the value from the in-between computation
435 bracket before after thing =
436 block (do
437 a <- before
438 r <- catchException
439 (unblock (thing a))
440 (\e -> do { after a; throw e })
441 after a
442 return r
443 )
444 #endif