copyCString* should be in IO. Spotted by Tomasz Zielonka
[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 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 and changing the size of a file
61
62 hFileSize, -- :: Handle -> IO Integer
63 #ifdef __GLASGOW_HASKELL__
64 hSetFileSize, -- :: Handle -> Integer -> IO ()
65 #endif
66
67 -- ** Detecting the end of input
68
69 hIsEOF, -- :: Handle -> IO Bool
70 isEOF, -- :: IO Bool
71
72 -- ** Buffering operations
73
74 BufferMode(NoBuffering,LineBuffering,BlockBuffering),
75 hSetBuffering, -- :: Handle -> BufferMode -> IO ()
76 hGetBuffering, -- :: Handle -> IO BufferMode
77 hFlush, -- :: Handle -> IO ()
78
79 -- ** Repositioning handles
80
81 hGetPosn, -- :: Handle -> IO HandlePosn
82 hSetPosn, -- :: HandlePosn -> IO ()
83 HandlePosn, -- abstract, instance of: Eq, Show.
84
85 hSeek, -- :: Handle -> SeekMode -> Integer -> IO ()
86 SeekMode(AbsoluteSeek,RelativeSeek,SeekFromEnd),
87 #if !defined(__NHC__)
88 hTell, -- :: Handle -> IO Integer
89 #endif
90
91 -- ** Handle properties
92
93 hIsOpen, hIsClosed, -- :: Handle -> IO Bool
94 hIsReadable, hIsWritable, -- :: Handle -> IO Bool
95 hIsSeekable, -- :: Handle -> IO Bool
96
97 -- ** Terminal operations
98
99 #if !defined(__NHC__)
100 hIsTerminalDevice, -- :: Handle -> IO Bool
101
102 hSetEcho, -- :: Handle -> Bool -> IO ()
103 hGetEcho, -- :: Handle -> IO Bool
104 #endif
105
106 -- ** Showing handle state
107
108 #ifdef __GLASGOW_HASKELL__
109 hShow, -- :: Handle -> IO String
110 #endif
111
112 -- * Text input and output
113
114 -- ** Text input
115
116 hWaitForInput, -- :: Handle -> Int -> IO Bool
117 hReady, -- :: Handle -> IO Bool
118 hGetChar, -- :: Handle -> IO Char
119 hGetLine, -- :: Handle -> IO [Char]
120 hLookAhead, -- :: Handle -> IO Char
121 hGetContents, -- :: Handle -> IO [Char]
122
123 -- ** Text output
124
125 hPutChar, -- :: Handle -> Char -> IO ()
126 hPutStr, -- :: Handle -> [Char] -> IO ()
127 hPutStrLn, -- :: Handle -> [Char] -> IO ()
128 hPrint, -- :: Show a => Handle -> a -> IO ()
129
130 -- ** Special cases for standard input and output
131
132 -- | These functions are also exported by the "Prelude".
133
134 interact, -- :: (String -> String) -> IO ()
135 putChar, -- :: Char -> IO ()
136 putStr, -- :: String -> IO ()
137 putStrLn, -- :: String -> IO ()
138 print, -- :: Show a => a -> IO ()
139 getChar, -- :: IO Char
140 getLine, -- :: IO String
141 getContents, -- :: IO String
142 readIO, -- :: Read a => String -> IO a
143 readLn, -- :: Read a => IO a
144
145 -- * Binary input and output
146
147 openBinaryFile, -- :: FilePath -> IOMode -> IO Handle
148 hSetBinaryMode, -- :: Handle -> Bool -> IO ()
149 #if !defined(__NHC__)
150 hPutBuf, -- :: Handle -> Ptr a -> Int -> IO ()
151 hGetBuf, -- :: Handle -> Ptr a -> Int -> IO Int
152 #endif
153 #if !defined(__NHC__) && !defined(__HUGS__)
154 hPutBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
155 hGetBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
156 #endif
157
158 -- * Temporary files
159
160 #ifdef __GLASGOW_HASKELL__
161 openTempFile,
162 openBinaryTempFile,
163 #endif
164 ) where
165
166 #ifdef __GLASGOW_HASKELL__
167 import GHC.Base
168 import GHC.IOBase -- Together these four Prelude modules define
169 import GHC.Handle -- all the stuff exported by IO for the GHC version
170 import GHC.IO
171 import GHC.Exception
172 import GHC.Num
173 import GHC.Read
174 import GHC.Show
175 #endif
176
177 #ifdef __HUGS__
178 import Hugs.IO
179 import Hugs.IOExts
180 import Hugs.IORef
181 import Hugs.Prelude ( throw, Exception(NonTermination) )
182 import System.IO.Unsafe ( unsafeInterleaveIO )
183 #endif
184
185 #ifdef __NHC__
186 import IO
187 ( Handle ()
188 , HandlePosn ()
189 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
190 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
191 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
192 , stdin, stdout, stderr
193 , openFile -- :: FilePath -> IOMode -> IO Handle
194 , hClose -- :: Handle -> IO ()
195 , hFileSize -- :: Handle -> IO Integer
196 , hIsEOF -- :: Handle -> IO Bool
197 , isEOF -- :: IO Bool
198 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
199 , hGetBuffering -- :: Handle -> IO BufferMode
200 , hFlush -- :: Handle -> IO ()
201 , hGetPosn -- :: Handle -> IO HandlePosn
202 , hSetPosn -- :: HandlePosn -> IO ()
203 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
204 , hWaitForInput -- :: Handle -> Int -> IO Bool
205 , hGetChar -- :: Handle -> IO Char
206 , hGetLine -- :: Handle -> IO [Char]
207 , hLookAhead -- :: Handle -> IO Char
208 , hGetContents -- :: Handle -> IO [Char]
209 , hPutChar -- :: Handle -> Char -> IO ()
210 , hPutStr -- :: Handle -> [Char] -> IO ()
211 , hPutStrLn -- :: Handle -> [Char] -> IO ()
212 , hPrint -- :: Handle -> [Char] -> IO ()
213 , hReady -- :: Handle -> [Char] -> IO ()
214 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
215 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
216 , hIsSeekable -- :: Handle -> IO Bool
217
218 , IO ()
219 , FilePath -- :: String
220 )
221 import NHC.IOExtras (fixIO)
222 #endif
223
224 -- -----------------------------------------------------------------------------
225 -- Standard IO
226
227 #ifdef __GLASGOW_HASKELL__
228 -- | Write a character to the standard output device
229 -- (same as 'hPutChar' 'stdout').
230
231 putChar :: Char -> IO ()
232 putChar c = hPutChar stdout c
233
234 -- | Write a string to the standard output device
235 -- (same as 'hPutStr' 'stdout').
236
237 putStr :: String -> IO ()
238 putStr s = hPutStr stdout s
239
240 -- | The same as 'putStr', but adds a newline character.
241
242 putStrLn :: String -> IO ()
243 putStrLn s = do putStr s
244 putChar '\n'
245
246 -- | The 'print' function outputs a value of any printable type to the
247 -- standard output device.
248 -- Printable types are those that are instances of class 'Show'; 'print'
249 -- converts values to strings for output using the 'show' operation and
250 -- adds a newline.
251 --
252 -- For example, a program to print the first 20 integers and their
253 -- powers of 2 could be written as:
254 --
255 -- > main = print ([(n, 2^n) | n <- [0..19]])
256
257 print :: Show a => a -> IO ()
258 print x = putStrLn (show x)
259
260 -- | Read a character from the standard input device
261 -- (same as 'hGetChar' 'stdin').
262
263 getChar :: IO Char
264 getChar = hGetChar stdin
265
266 -- | Read a line from the standard input device
267 -- (same as 'hGetLine' 'stdin').
268
269 getLine :: IO String
270 getLine = hGetLine stdin
271
272 -- | The 'getContents' operation returns all user input as a single string,
273 -- which is read lazily as it is needed
274 -- (same as 'hGetContents' 'stdin').
275
276 getContents :: IO String
277 getContents = hGetContents stdin
278
279 -- | The 'interact' function takes a function of type @String->String@
280 -- as its argument. The entire input from the standard input device is
281 -- passed to this function as its argument, and the resulting string is
282 -- output on the standard output device.
283
284 interact :: (String -> String) -> IO ()
285 interact f = do s <- getContents
286 putStr (f s)
287
288 -- | The 'readFile' function reads a file and
289 -- returns the contents of the file as a string.
290 -- The file is read lazily, on demand, as with 'getContents'.
291
292 readFile :: FilePath -> IO String
293 readFile name = openFile name ReadMode >>= hGetContents
294
295 -- | The computation 'writeFile' @file str@ function writes the string @str@,
296 -- to the file @file@.
297 writeFile :: FilePath -> String -> IO ()
298 writeFile f txt = bracket (openFile f WriteMode) hClose
299 (\hdl -> hPutStr hdl txt)
300
301 -- | The computation 'appendFile' @file str@ function appends the string @str@,
302 -- to the file @file@.
303 --
304 -- Note that 'writeFile' and 'appendFile' write a literal string
305 -- to a file. To write a value of any printable type, as with 'print',
306 -- use the 'show' function to convert the value to a string first.
307 --
308 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
309
310 appendFile :: FilePath -> String -> IO ()
311 appendFile f txt = bracket (openFile f AppendMode) hClose
312 (\hdl -> hPutStr hdl txt)
313
314 -- | The 'readLn' function combines 'getLine' and 'readIO'.
315
316 readLn :: Read a => IO a
317 readLn = do l <- getLine
318 r <- readIO l
319 return r
320
321 -- | The 'readIO' function is similar to 'read' except that it signals
322 -- parse failure to the 'IO' monad instead of terminating the program.
323
324 readIO :: Read a => String -> IO a
325 readIO s = case (do { (x,t) <- reads s ;
326 ("","") <- lex t ;
327 return x }) of
328 [x] -> return x
329 [] -> ioError (userError "Prelude.readIO: no parse")
330 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
331 #endif /* __GLASGOW_HASKELL__ */
332
333 #ifndef __NHC__
334 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
335 -- available for input from handle @hdl@.
336 --
337 -- This operation may fail with:
338 --
339 -- * 'System.IO.Error.isEOFError' if the end of file has been reached.
340
341 hReady :: Handle -> IO Bool
342 hReady h = hWaitForInput h 0
343
344 -- | The same as 'hPutStr', but adds a newline character.
345
346 hPutStrLn :: Handle -> String -> IO ()
347 hPutStrLn hndl str = do
348 hPutStr hndl str
349 hPutChar hndl '\n'
350
351 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
352 -- given by the 'shows' function to the file or channel managed by @hdl@
353 -- and appends a newline.
354 --
355 -- This operation may fail with:
356 --
357 -- * 'System.IO.Error.isFullError' if the device is full; or
358 --
359 -- * 'System.IO.Error.isPermissionError' if another system resource limit would be exceeded.
360
361 hPrint :: Show a => Handle -> a -> IO ()
362 hPrint hdl = hPutStrLn hdl . show
363 #endif /* !__NHC__ */
364
365 -- ---------------------------------------------------------------------------
366 -- fixIO
367
368 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
369 fixIO :: (a -> IO a) -> IO a
370 fixIO k = do
371 ref <- newIORef (throw NonTermination)
372 ans <- unsafeInterleaveIO (readIORef ref)
373 result <- k ans
374 writeIORef ref result
375 return result
376
377 -- NOTE: we do our own explicit black holing here, because GHC's lazy
378 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
379 -- computation a few times before it notices the loop, which is wrong.
380 #endif
381
382 #if defined(__NHC__)
383 -- Assume a unix platform, where text and binary I/O are identical.
384 openBinaryFile = openFile
385 hSetBinaryMode _ _ = return ()
386 #endif
387
388 -- $locking
389 -- Implementations should enforce as far as possible, at least locally to the
390 -- Haskell process, multiple-reader single-writer locking on files.
391 -- That is, /there may either be many handles on the same file which manage
392 -- input, or just one handle on the file which manages output/. If any
393 -- open or semi-closed handle is managing a file for output, no new
394 -- handle can be allocated for that file. If any open or semi-closed
395 -- handle is managing a file for input, new handles can only be allocated
396 -- if they do not manage output. Whether two files are the same is
397 -- implementation-dependent, but they should normally be the same if they
398 -- have the same absolute path name and neither has been renamed, for
399 -- example.
400 --
401 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
402 -- the file until the entire contents of the file have been consumed.
403 -- It follows that an attempt to write to a file (using 'writeFile', for
404 -- example) that was earlier opened by 'readFile' will usually result in
405 -- failure with 'System.IO.Error.isAlreadyInUseError'.
406
407 -- -----------------------------------------------------------------------------
408 -- Utils
409
410 #ifdef __GLASGOW_HASKELL__
411 -- Copied here to avoid recursive dependency with Control.Exception
412 bracket
413 :: IO a -- ^ computation to run first (\"acquire resource\")
414 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
415 -> (a -> IO c) -- ^ computation to run in-between
416 -> IO c -- returns the value from the in-between computation
417 bracket before after thing =
418 block (do
419 a <- before
420 r <- catchException
421 (unblock (thing a))
422 (\e -> do { after a; throw e })
423 after a
424 return r
425 )
426 #endif