add install-includes: field
[packages/pretty.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 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
156 #endif
157
158 -- * Temporary files (not portable: GHC only)
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 Control.Exception ( bracket )
183 import System.IO.Unsafe ( unsafeInterleaveIO )
184 #endif
185
186 #ifdef __NHC__
187 import IO
188 ( Handle ()
189 , HandlePosn ()
190 , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
191 , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
192 , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
193 , stdin, stdout, stderr
194 , openFile -- :: FilePath -> IOMode -> IO Handle
195 , hClose -- :: Handle -> IO ()
196 , hFileSize -- :: Handle -> IO Integer
197 , hIsEOF -- :: Handle -> IO Bool
198 , isEOF -- :: IO Bool
199 , hSetBuffering -- :: Handle -> BufferMode -> IO ()
200 , hGetBuffering -- :: Handle -> IO BufferMode
201 , hFlush -- :: Handle -> IO ()
202 , hGetPosn -- :: Handle -> IO HandlePosn
203 , hSetPosn -- :: HandlePosn -> IO ()
204 , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
205 , hWaitForInput -- :: Handle -> Int -> IO Bool
206 , hGetChar -- :: Handle -> IO Char
207 , hGetLine -- :: Handle -> IO [Char]
208 , hLookAhead -- :: Handle -> IO Char
209 , hGetContents -- :: Handle -> IO [Char]
210 , hPutChar -- :: Handle -> Char -> IO ()
211 , hPutStr -- :: Handle -> [Char] -> IO ()
212 , hPutStrLn -- :: Handle -> [Char] -> IO ()
213 , hPrint -- :: Handle -> [Char] -> IO ()
214 , hReady -- :: Handle -> [Char] -> IO ()
215 , hIsOpen, hIsClosed -- :: Handle -> IO Bool
216 , hIsReadable, hIsWritable -- :: Handle -> IO Bool
217 , hIsSeekable -- :: Handle -> IO Bool
218 , bracket
219
220 , IO ()
221 , FilePath -- :: String
222 )
223 import NHC.IOExtras (fixIO, hPutBuf, hGetBuf)
224 import NHC.FFI (Ptr)
225 #endif
226
227 -- -----------------------------------------------------------------------------
228 -- Standard IO
229
230 #ifdef __GLASGOW_HASKELL__
231 -- | Write a character to the standard output device
232 -- (same as 'hPutChar' 'stdout').
233
234 putChar :: Char -> IO ()
235 putChar c = hPutChar stdout c
236
237 -- | Write a string to the standard output device
238 -- (same as 'hPutStr' 'stdout').
239
240 putStr :: String -> IO ()
241 putStr s = hPutStr stdout s
242
243 -- | The same as 'putStr', but adds a newline character.
244
245 putStrLn :: String -> IO ()
246 putStrLn s = do putStr s
247 putChar '\n'
248
249 -- | The 'print' function outputs a value of any printable type to the
250 -- standard output device.
251 -- Printable types are those that are instances of class 'Show'; 'print'
252 -- converts values to strings for output using the 'show' operation and
253 -- adds a newline.
254 --
255 -- For example, a program to print the first 20 integers and their
256 -- powers of 2 could be written as:
257 --
258 -- > main = print ([(n, 2^n) | n <- [0..19]])
259
260 print :: Show a => a -> IO ()
261 print x = putStrLn (show x)
262
263 -- | Read a character from the standard input device
264 -- (same as 'hGetChar' 'stdin').
265
266 getChar :: IO Char
267 getChar = hGetChar stdin
268
269 -- | Read a line from the standard input device
270 -- (same as 'hGetLine' 'stdin').
271
272 getLine :: IO String
273 getLine = hGetLine stdin
274
275 -- | The 'getContents' operation returns all user input as a single string,
276 -- which is read lazily as it is needed
277 -- (same as 'hGetContents' 'stdin').
278
279 getContents :: IO String
280 getContents = hGetContents stdin
281
282 -- | The 'interact' function takes a function of type @String->String@
283 -- as its argument. The entire input from the standard input device is
284 -- passed to this function as its argument, and the resulting string is
285 -- output on the standard output device.
286
287 interact :: (String -> String) -> IO ()
288 interact f = do s <- getContents
289 putStr (f s)
290
291 -- | The 'readFile' function reads a file and
292 -- returns the contents of the file as a string.
293 -- The file is read lazily, on demand, as with 'getContents'.
294
295 readFile :: FilePath -> IO String
296 readFile name = openFile name ReadMode >>= hGetContents
297
298 -- | The computation 'writeFile' @file str@ function writes the string @str@,
299 -- to the file @file@.
300 writeFile :: FilePath -> String -> IO ()
301 writeFile f txt = withFile f WriteMode (\ hdl -> hPutStr hdl txt)
302
303 -- | The computation 'appendFile' @file str@ function appends the string @str@,
304 -- to the file @file@.
305 --
306 -- Note that 'writeFile' and 'appendFile' write a literal string
307 -- to a file. To write a value of any printable type, as with 'print',
308 -- use the 'show' function to convert the value to a string first.
309 --
310 -- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
311
312 appendFile :: FilePath -> String -> IO ()
313 appendFile f txt = withFile f AppendMode (\ hdl -> hPutStr hdl txt)
314
315 -- | The 'readLn' function combines 'getLine' and 'readIO'.
316
317 readLn :: Read a => IO a
318 readLn = do l <- getLine
319 r <- readIO l
320 return r
321
322 -- | The 'readIO' function is similar to 'read' except that it signals
323 -- parse failure to the 'IO' monad instead of terminating the program.
324
325 readIO :: Read a => String -> IO a
326 readIO s = case (do { (x,t) <- reads s ;
327 ("","") <- lex t ;
328 return x }) of
329 [x] -> return x
330 [] -> ioError (userError "Prelude.readIO: no parse")
331 _ -> ioError (userError "Prelude.readIO: ambiguous parse")
332 #endif /* __GLASGOW_HASKELL__ */
333
334 #ifndef __NHC__
335 -- | Computation 'hReady' @hdl@ indicates whether at least one item is
336 -- available for input from handle @hdl@.
337 --
338 -- This operation may fail with:
339 --
340 -- * 'System.IO.Error.isEOFError' if the end of file has been reached.
341
342 hReady :: Handle -> IO Bool
343 hReady h = hWaitForInput h 0
344
345 -- | The same as 'hPutStr', but adds a newline character.
346
347 hPutStrLn :: Handle -> String -> IO ()
348 hPutStrLn hndl str = do
349 hPutStr hndl str
350 hPutChar hndl '\n'
351
352 -- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
353 -- given by the 'shows' function to the file or channel managed by @hdl@
354 -- and appends a newline.
355 --
356 -- This operation may fail with:
357 --
358 -- * 'System.IO.Error.isFullError' if the device is full; or
359 --
360 -- * 'System.IO.Error.isPermissionError' if another system resource limit would be exceeded.
361
362 hPrint :: Show a => Handle -> a -> IO ()
363 hPrint hdl = hPutStrLn hdl . show
364 #endif /* !__NHC__ */
365
366 -- | @'withFile' name mode act@ opens a file using 'openFile' and passes
367 -- the resulting handle to the computation @act@. The handle will be
368 -- closed on exit from 'withFile', whether by normal termination or by
369 -- raising an exception.
370 withFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
371 withFile name mode = bracket (openFile name mode) hClose
372
373 -- | @'withBinaryFile' name mode act@ opens a file using 'openBinaryFile'
374 -- and passes the resulting handle to the computation @act@. The handle
375 -- will be closed on exit from 'withBinaryFile', whether by normal
376 -- termination or by raising an exception.
377 withBinaryFile :: FilePath -> IOMode -> (Handle -> IO r) -> IO r
378 withBinaryFile name mode = bracket (openBinaryFile name mode) hClose
379
380 -- ---------------------------------------------------------------------------
381 -- fixIO
382
383 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
384 fixIO :: (a -> IO a) -> IO a
385 fixIO k = do
386 ref <- newIORef (throw NonTermination)
387 ans <- unsafeInterleaveIO (readIORef ref)
388 result <- k ans
389 writeIORef ref result
390 return result
391
392 -- NOTE: we do our own explicit black holing here, because GHC's lazy
393 -- blackholing isn't enough. In an infinite loop, GHC may run the IO
394 -- computation a few times before it notices the loop, which is wrong.
395 #endif
396
397 #if defined(__NHC__)
398 -- Assume a unix platform, where text and binary I/O are identical.
399 openBinaryFile = openFile
400 hSetBinaryMode _ _ = return ()
401 #endif
402
403 -- $locking
404 -- Implementations should enforce as far as possible, at least locally to the
405 -- Haskell process, multiple-reader single-writer locking on files.
406 -- That is, /there may either be many handles on the same file which manage
407 -- input, or just one handle on the file which manages output/. If any
408 -- open or semi-closed handle is managing a file for output, no new
409 -- handle can be allocated for that file. If any open or semi-closed
410 -- handle is managing a file for input, new handles can only be allocated
411 -- if they do not manage output. Whether two files are the same is
412 -- implementation-dependent, but they should normally be the same if they
413 -- have the same absolute path name and neither has been renamed, for
414 -- example.
415 --
416 -- /Warning/: the 'readFile' operation holds a semi-closed handle on
417 -- the file until the entire contents of the file have been consumed.
418 -- It follows that an attempt to write to a file (using 'writeFile', for
419 -- example) that was earlier opened by 'readFile' will usually result in
420 -- failure with 'System.IO.Error.isAlreadyInUseError'.
421
422 -- -----------------------------------------------------------------------------
423 -- Utils
424
425 #ifdef __GLASGOW_HASKELL__
426 -- Copied here to avoid recursive dependency with Control.Exception
427 bracket
428 :: IO a -- ^ computation to run first (\"acquire resource\")
429 -> (a -> IO b) -- ^ computation to run last (\"release resource\")
430 -> (a -> IO c) -- ^ computation to run in-between
431 -> IO c -- returns the value from the in-between computation
432 bracket before after thing =
433 block (do
434 a <- before
435 r <- catchException
436 (unblock (thing a))
437 (\e -> do { after a; throw e })
438 after a
439 return r
440 )
441 #endif