Chapter 33
Foreign.Marshal.Error

throwIf

::	(a -> Bool)	error condition on the result of the IO action
->	(a -> String)	computes an error message from erroneous results of the IO action
->	IO a	the IO action to be executed
->	IO a

Execute an IO action, throwing a userError if the predicate yields True when applied to the result returned by the IO action. If no exception is raised, return the result of the computation.

throwIf_ :: (a -> Bool) -> (a -> String) -> IO a -> IO ()

Like throwIf, but discarding the result

throwIfNeg :: (Ord a, Num a) => (a -> String) -> IO a -> IO a

Guards against negative result values

throwIfNeg_ :: (Ord a, Num a) => (a -> String) -> IO a -> IO ()

Like throwIfNeg, but discarding the result

throwIfNull :: String -> IO (Ptr a) -> IO (Ptr a)

Guards against null pointers

void :: IO a -> IO ()

Discard the return value of an IO action