{-# LANGUAGE CPP #-} #if __GLASGOW_HASKELL__ >= 701 {-# LANGUAGE Safe #-} #endif 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 import System.IO.Error -- | 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 -- | The construct 'try' @comp@ exposes IO errors which occur within a -- computation, and which are not fully handled. -- -- Non-I\/O exceptions are not caught by this variant; to catch all -- exceptions, use 'Control.Exception.try' from "Control.Exception". try :: IO a -> IO (Either IOError a) try f = catch (do r <- f return (Right r)) (return . Left)