-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
--- Stability : provisional
+-- Stability : stable
-- Portability : portable
--
-- The standard IO library.
-----------------------------------------------------------------------------
module System.IO (
+ -- * The IO monad
+
+ IO, -- instance MonadFix
+ fixIO, -- :: (a -> IO a) -> IO a
+
+ -- * Files and handles
+
+ FilePath, -- :: String
+
Handle, -- abstract, instance of: Eq, Show.
- HandlePosn(..), -- abstract, instance of: Eq, Show.
- IOMode(ReadMode,WriteMode,AppendMode,ReadWriteMode),
- BufferMode(NoBuffering,LineBuffering,BlockBuffering),
- SeekMode(AbsoluteSeek,RelativeSeek,SeekFromEnd),
+ -- ** Standard handles
+
+ -- | Three handles are allocated during program initialisation,
+ -- and are initially open.
stdin, stdout, stderr, -- :: Handle
+ -- * Opening and closing files
+
+ -- ** Opening files
+
openFile, -- :: FilePath -> IOMode -> IO Handle
+ IOMode(ReadMode,WriteMode,AppendMode,ReadWriteMode),
+
+ -- ** Closing files
+
hClose, -- :: Handle -> IO ()
+
+ -- ** Special cases
+
+ -- | These functions are also exported by the "Prelude".
+
+ readFile, -- :: FilePath -> IO String
+ writeFile, -- :: FilePath -> String -> IO ()
+ appendFile, -- :: FilePath -> String -> IO ()
+
+ -- ** File locking
+
+ -- $locking
+
+ -- * Operations on handles
+
+ -- ** Determining the size of a file
+
hFileSize, -- :: Handle -> IO Integer
+
+ -- ** Detecting the end of input
+
hIsEOF, -- :: Handle -> IO Bool
isEOF, -- :: IO Bool
+ -- ** Buffering operations
+
+ BufferMode(NoBuffering,LineBuffering,BlockBuffering),
hSetBuffering, -- :: Handle -> BufferMode -> IO ()
hGetBuffering, -- :: Handle -> IO BufferMode
hFlush, -- :: Handle -> IO ()
+
+ -- ** Repositioning handles
+
hGetPosn, -- :: Handle -> IO HandlePosn
hSetPosn, -- :: HandlePosn -> IO ()
+ HandlePosn, -- abstract, instance of: Eq, Show.
+
hSeek, -- :: Handle -> SeekMode -> Integer -> IO ()
+ SeekMode(AbsoluteSeek,RelativeSeek,SeekFromEnd),
+#if !defined(__NHC__)
hTell, -- :: Handle -> IO Integer
+#endif
+
+ -- ** Handle properties
+
+ hIsOpen, hIsClosed, -- :: Handle -> IO Bool
+ hIsReadable, hIsWritable, -- :: Handle -> IO Bool
+ hIsSeekable, -- :: Handle -> IO Bool
+
+ -- ** Terminal operations
+
+#if !defined(__HUGS__) && !defined(__NHC__)
+ hIsTerminalDevice, -- :: Handle -> IO Bool
+
+ hSetEcho, -- :: Handle -> Bool -> IO ()
+ hGetEcho, -- :: Handle -> IO Bool
+#endif
+
+ -- ** Showing handle state
+
+#ifdef __GLASGOW_HASKELL__
+ hShow, -- :: Handle -> IO String
+#endif
+
+ -- * Text input and output
+
+ -- ** Text input
+
hWaitForInput, -- :: Handle -> Int -> IO Bool
hReady, -- :: Handle -> IO Bool
hGetChar, -- :: Handle -> IO Char
hGetLine, -- :: Handle -> IO [Char]
hLookAhead, -- :: Handle -> IO Char
hGetContents, -- :: Handle -> IO [Char]
+
+ -- ** Text output
+
hPutChar, -- :: Handle -> Char -> IO ()
hPutStr, -- :: Handle -> [Char] -> IO ()
hPutStrLn, -- :: Handle -> [Char] -> IO ()
hPrint, -- :: Show a => Handle -> a -> IO ()
- hIsOpen, hIsClosed, -- :: Handle -> IO Bool
- hIsReadable, hIsWritable, -- :: Handle -> IO Bool
- hIsSeekable, -- :: Handle -> IO Bool
- isAlreadyExistsError, isDoesNotExistError, -- :: IOError -> Bool
- isAlreadyInUseError, isFullError,
- isEOFError, isIllegalOperation,
- isPermissionError, isUserError,
-
- ioeGetErrorString, -- :: IOError -> String
- ioeGetHandle, -- :: IOError -> Maybe Handle
- ioeGetFileName, -- :: IOError -> Maybe FilePath
+ -- ** Special cases for standard input and output
- try, -- :: IO a -> IO (Either IOError a)
- bracket, -- :: IO a -> (a -> IO b) -> (a -> IO c) -> IO c
- bracket_, -- :: IO a -> (a -> IO b) -> IO c -> IO c
+ -- | These functions are also exported by the "Prelude".
- -- Non-standard extension (but will hopefully become standard with 1.5) is
- -- to export the Prelude io functions via IO (in addition to exporting them
- -- from the prelude...for now.)
- IO, -- instance MonadFix
- FilePath, -- :: String
- IOError,
- ioError, -- :: IOError -> IO a
- userError, -- :: String -> IOError
- catch, -- :: IO a -> (IOError -> IO a) -> IO a
interact, -- :: (String -> String) -> IO ()
-
putChar, -- :: Char -> IO ()
putStr, -- :: String -> IO ()
putStrLn, -- :: String -> IO ()
getChar, -- :: IO Char
getLine, -- :: IO String
getContents, -- :: IO String
- readFile, -- :: FilePath -> IO String
- writeFile, -- :: FilePath -> String -> IO ()
- appendFile, -- :: FilePath -> String -> IO ()
readIO, -- :: Read a => String -> IO a
readLn, -- :: Read a => IO a
-#ifndef __HUGS__
+ -- * Binary input and output
+
+#if !defined(__NHC__)
+ openBinaryFile, -- :: FilePath -> IOMode -> IO Handle
+#endif
+
+#if !defined(__HUGS__) && !defined(__NHC__)
+ hSetBinaryMode, -- :: Handle -> Bool -> IO ()
hPutBuf, -- :: Handle -> Ptr a -> Int -> IO ()
hGetBuf, -- :: Handle -> Ptr a -> Int -> IO Int
+ hPutBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
+ hGetBufNonBlocking, -- :: Handle -> Ptr a -> Int -> IO Int
#endif
-
- fixIO, -- :: (a -> IO a) -> IO a
-
-#ifndef __HUGS__
- hSetEcho, -- :: Handle -> Bool -> IO ()
- hGetEcho, -- :: Handle -> IO Bool
- hIsTerminalDevice, -- :: Handle -> IO Bool
-#endif
+ module System.IO.Error,
) where
#ifdef __GLASGOW_HASKELL__
import Hugs.IOExts
#endif
-import System.IO.Error
+#ifdef __NHC__
+import IO
+ ( Handle ()
+ , HandlePosn ()
+ , IOMode (ReadMode,WriteMode,AppendMode,ReadWriteMode)
+ , BufferMode (NoBuffering,LineBuffering,BlockBuffering)
+ , SeekMode (AbsoluteSeek,RelativeSeek,SeekFromEnd)
+ , stdin, stdout, stderr
+ , openFile -- :: FilePath -> IOMode -> IO Handle
+ , hClose -- :: Handle -> IO ()
+ , hFileSize -- :: Handle -> IO Integer
+ , hIsEOF -- :: Handle -> IO Bool
+ , isEOF -- :: IO Bool
+ , hSetBuffering -- :: Handle -> BufferMode -> IO ()
+ , hGetBuffering -- :: Handle -> IO BufferMode
+ , hFlush -- :: Handle -> IO ()
+ , hGetPosn -- :: Handle -> IO HandlePosn
+ , hSetPosn -- :: HandlePosn -> IO ()
+ , hSeek -- :: Handle -> SeekMode -> Integer -> IO ()
+ , hWaitForInput -- :: Handle -> Int -> IO Bool
+ , hGetChar -- :: Handle -> IO Char
+ , hGetLine -- :: Handle -> IO [Char]
+ , hLookAhead -- :: Handle -> IO Char
+ , hGetContents -- :: Handle -> IO [Char]
+ , hPutChar -- :: Handle -> Char -> IO ()
+ , hPutStr -- :: Handle -> [Char] -> IO ()
+ , hIsOpen, hIsClosed -- :: Handle -> IO Bool
+ , hIsReadable, hIsWritable -- :: Handle -> IO Bool
+ , hIsSeekable -- :: Handle -> IO Bool
+
+ , IO ()
+ , FilePath -- :: String
+ )
+import NHC.IOExtras (fixIO)
+#endif
+
+import System.IO.Error (
+ isAlreadyExistsError, isDoesNotExistError, -- :: IOError -> Bool
+ isAlreadyInUseError, isFullError,
+ isEOFError, isIllegalOperation,
+ isPermissionError, isUserError,
+
+ ioeGetErrorString, -- :: IOError -> String
+ ioeGetHandle, -- :: IOError -> Maybe Handle
+ ioeGetFileName, -- :: IOError -> Maybe FilePath
+
+ try, -- :: IO a -> IO (Either IOError a)
+
+ -- re-exports of Prelude names
+ IOError,
+ ioError, -- :: IOError -> IO a
+ userError, -- :: String -> IOError
+ catch -- :: IO a -> (IOError -> IO a) -> IO a
+ )
-- -----------------------------------------------------------------------------
-- Standard IO
#ifndef __HUGS__
+-- | Write a character to the standard output device
+-- (same as 'hPutChar' 'stdout').
+
putChar :: Char -> IO ()
putChar c = hPutChar stdout c
+-- | Write a string to the standard output device
+-- (same as 'hPutStr' 'stdout').
+
putStr :: String -> IO ()
putStr s = hPutStr stdout s
+-- | The same as 'putStrLn', but adds a newline character.
+
putStrLn :: String -> IO ()
putStrLn s = do putStr s
putChar '\n'
+-- | The 'print' function outputs a value of any printable type to the
+-- standard output device.
+-- Printable types are those that are instances of class 'Show'; 'print'
+-- converts values to strings for output using the 'show' operation and
+-- adds a newline.
+--
+-- For example, a program to print the first 20 integers and their
+-- powers of 2 could be written as:
+--
+-- > main = print ([(n, 2^n) | n <- [0..19]])
+
print :: Show a => a -> IO ()
print x = putStrLn (show x)
+-- | Read a character from the standard input device
+-- (same as 'hGetChar' 'stdin').
+
getChar :: IO Char
getChar = hGetChar stdin
+-- | Read a line from the standard input device
+-- (same as 'hGetLine' 'stdin').
+
getLine :: IO String
getLine = hGetLine stdin
+-- | The 'getContents' operation returns all user input as a single string,
+-- which is read lazily as it is needed
+-- (same as 'hGetContents' 'stdin').
+
getContents :: IO String
getContents = hGetContents stdin
+-- | The 'interact' function takes a function of type @String->String@
+-- as its argument. The entire input from the standard input device is
+-- passed to this function as its argument, and the resulting string is
+-- output on the standard output device.
+
interact :: (String -> String) -> IO ()
interact f = do s <- getContents
putStr (f s)
+-- | The 'readFile' function reads a file and
+-- returns the contents of the file as a string.
+-- The file is read lazily, on demand, as with 'getContents'.
+
readFile :: FilePath -> IO String
readFile name = openFile name ReadMode >>= hGetContents
+-- | The computation 'writeFile' @file str@ function writes the string @str@,
+-- to the file @file@.
+
writeFile :: FilePath -> String -> IO ()
writeFile name str = do
hdl <- openFile name WriteMode
hPutStr hdl str
hClose hdl
+-- | The computation 'appendFile' @file str@ function appends the string @str@,
+-- to the file @file@.
+--
+-- Note that 'writeFile' and 'appendFile' write a literal string
+-- to a file. To write a value of any printable type, as with 'print',
+-- use the 'show' function to convert the value to a string first.
+--
+-- > main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
+
appendFile :: FilePath -> String -> IO ()
appendFile name str = do
hdl <- openFile name AppendMode
hPutStr hdl str
hClose hdl
+-- | The 'readLn' function combines 'getLine' and 'readIO'.
+
readLn :: Read a => IO a
readLn = do l <- getLine
r <- readIO l
return r
--- raises an exception instead of an error
+-- | The 'readIO' function is similar to 'read' except that it signals
+-- parse failure to the 'IO' monad instead of terminating the program.
+
readIO :: Read a => String -> IO a
readIO s = case (do { (x,t) <- reads s ;
("","") <- lex t ;
_ -> ioError (userError "Prelude.readIO: ambiguous parse")
#endif /* __HUGS__ */
+-- | Computation 'hReady' @hdl@ indicates whether at least one item is
+-- available for input from handle @hdl@.
+--
+-- This operation may fail with:
+--
+-- * 'isEOFError' if the end of file has been reached.
+
hReady :: Handle -> IO Bool
hReady h = hWaitForInput h 0
+-- | The same as 'hPutStr', but adds a newline character.
+
hPutStrLn :: Handle -> String -> IO ()
hPutStrLn hndl str = do
hPutStr hndl str
hPutChar hndl '\n'
+-- | Computation 'hPrint' @hdl t@ writes the string representation of @t@
+-- given by the 'shows' function to the file or channel managed by @hdl@
+-- and appends a newline.
+--
+-- This operation may fail with:
+--
+-- * 'isFullError' if the device is full; or
+--
+-- * 'isPermissionError' if another system resource limit would be exceeded.
+
hPrint :: Show a => Handle -> a -> IO ()
hPrint hdl = hPutStrLn hdl . show
fixIO :: (a -> IO a) -> IO a
fixIO m = stToIO (fixST (ioToST . m))
#endif
+
+-- $locking
+-- Implementations should enforce as far as possible, at least locally to the
+-- Haskell process, multiple-reader single-writer locking on files.
+-- That is, /there may either be many handles on the same file which manage
+-- input, or just one handle on the file which manages output/. If any
+-- open or semi-closed handle is managing a file for output, no new
+-- handle can be allocated for that file. If any open or semi-closed
+-- handle is managing a file for input, new handles can only be allocated
+-- if they do not manage output. Whether two files are the same is
+-- implementation-dependent, but they should normally be the same if they
+-- have the same absolute path name and neither has been renamed, for
+-- example.
+--
+-- /Warning/: the 'readFile' operation holds a semi-closed handle on
+-- the file until the entire contents of the file have been consumed.
+-- It follows that an attempt to write to a file (using 'writeFile', for
+-- example) that was earlier opened by 'readFile' will usually result in
+-- failure with 'isAlreadyInUseError'.
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