base- Basic libraries

Safe HaskellTrustworthy



Routines for testing return values and raising a userError exception in case of values indicating an error state.





:: (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 ()Source

Like throwIf, but discarding the result

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

Guards against negative result values

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

Like throwIfNeg, but discarding the result

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

Guards against null pointers

void :: IO a -> IO ()Source

Deprecated: use Control.Monad.void instead

Discard the return value of an IO action