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|
module IO (
Handle, HandlePosn,
IOMode(ReadMode,WriteMode,AppendMode,ReadWriteMode),
BufferMode(NoBuffering,LineBuffering,BlockBuffering),
SeekMode(AbsoluteSeek,RelativeSeek,SeekFromEnd),
stdin, stdout, stderr,
openFile, hClose, hFileSize, hIsEOF, isEOF,
hSetBuffering, hGetBuffering, hFlush,
hGetPosn, hSetPosn, hSeek,
hWaitForInput, hReady, hGetChar, hGetLine, hLookAhead, hGetContents,
hPutChar, hPutStr, hPutStrLn, hPrint,
hIsOpen, hIsClosed, hIsReadable, hIsWritable, hIsSeekable,
isAlreadyExistsError, isDoesNotExistError, isAlreadyInUseError,
isFullError, isEOFError,
isIllegalOperation, isPermissionError, isUserError,
ioeGetErrorString, ioeGetHandle, ioeGetFileName,
try, bracket, bracket_,
-- ...and what the Prelude exports
IO, FilePath, IOError, ioError, userError, catch, interact,
putChar, putStr, putStrLn, print, getChar, getLine, getContents,
readFile, writeFile, appendFile, readIO, readLn
) where
import System.IO
-- | The 'bracket' function captures a common allocate, compute, deallocate
-- idiom in which the deallocation step must occur even in the case of an
-- error during computation. This is similar to try-catch-finally in Java.
--
-- This version handles only IO errors, as defined by Haskell 98.
-- The version of @bracket@ in "Control.Exception" handles all exceptions,
-- and should be used instead.
bracket :: IO a -> (a -> IO b) -> (a -> IO c) -> IO c
bracket before after m = do
x <- before
rs <- try (m x)
after x
case rs of
Right r -> return r
Left e -> ioError e
-- | A variant of 'bracket' where the middle computation doesn't want @x@.
--
-- This version handles only IO errors, as defined by Haskell 98.
-- The version of @bracket_@ in "Control.Exception" handles all exceptions,
-- and should be used instead.
bracket_ :: IO a -> (a -> IO b) -> IO c -> IO c
bracket_ before after m = do
x <- before
rs <- try m
after x
case rs of
Right r -> return r
Left e -> ioError e
|
