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