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module IO {- export list omitted -} where
-- Just provide an implementation of the system-independent
-- actions that IO exports.
try :: IO a -> IO (Either IOError a)
try f = catch (do r <- f
return (Right r))
(return . Left)
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
-- variant of the above where middle computation doesn't want x
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
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