Discussion: Add safeWithFile function

[David Feuer]

Some care is required to use withFile properly with lazy IO, and people
sometimes get it wrong. In some cases, readFile is a suitable replacement.
In other cases, however, it may be necessary to ensure the file gets closed
in a timely manner, and it may not be necessary to read the whole file. The
following seems to do the trick:

safeWithFile :: (NFData a) => String -> IOMode -> (Handle -> IO a) -> IO a
safeWithFile name mode f = withFile name mode $ f >=> (return $!!)


Sample use:

*SafeWithFile> safeWithFile "SafeWithFile.hs" ReadMode hGetContents >>=
putStr
module SafeWithFile (safeWithFile) where
import Control.DeepSeq
import System.IO
import Control.Monad

safeWithFile :: (NFData a) => String -> IOMode -> (Handle -> IO a) -> IO a
safeWithFile name mode f = withFile name mode $ f >=> (return $!!)
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