Imperative Object Destruction
Mon, 13 Nov 2000 02:33:29 -0800
At 2000-11-13 01:27, Chris Angus wrote:
>why not create an abstract datatype
>OpenFile a which is a monad
>data OpenFile a = OpenFile (Maybe FileHandle -> IO a)
>and create you operations in terms of this
>openFile :: String -> OpenFile ()
>count :: OpenFile Int
>read :: Int -> OpenFile [Byte]
>then you could habe a run function
>runOF :: OpenFile a -> IO a
>which ran whatever you wanted for the file and ensured tahthe file was
>closed correctly afterwards.
This is a slight generalisation of my scheme, from which
withFile :: OpenFile a -> String -> IO a
withFile operation name = runOF (openFile name >> operation)
>How we would do this with 2 files however I'm not so sure.
Looks like you can't.
This might work, however:
read :: (Int,Int) -> OpenFile IO [Byte]
write :: (Int,[Byte]) -> OpenFile IO ()
withFile :: OpenFile a -> String -> a
copyFile :: OpenFile OpenFile IO ()
withFile (withFile copyFile "dest") "source"
...but I'm not sure how to write copyFile.
Ashley Yakeley, Seattle WA