{-# LANGUAGE Trustworthy #-} {-# LANGUAGE CPP, NoImplicitPrelude #-} ----------------------------------------------------------------------------- -- | -- Module : Foreign.Marshal.Error -- Copyright : (c) The FFI task force 2001 -- License : BSD-style (see the file libraries/base/LICENSE) -- -- Maintainer : ffi@haskell.org -- Stability : provisional -- Portability : portable -- -- Routines for testing return values and raising a 'userError' exception -- in case of values indicating an error state. -- ----------------------------------------------------------------------------- module Foreign.Marshal.Error ( throwIf, throwIf_, throwIfNeg, throwIfNeg_, throwIfNull, -- Discard return value -- void ) where import Foreign.Ptr #ifdef __HADDOCK__ import Data.Bool import System.IO.Error #endif import GHC.Base import GHC.Num import GHC.IO.Exception -- exported functions -- ------------------ -- |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) -- ^ 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 throwIf pred msgfct act = do res <- act (if pred res then ioError . userError . msgfct else return) res -- |Like 'throwIf', but discarding the result -- throwIf_ :: (a -> Bool) -> (a -> String) -> IO a -> IO () throwIf_ pred msgfct act = void $ throwIf pred msgfct act -- |Guards against negative result values -- throwIfNeg :: (Ord a, Num a) => (a -> String) -> IO a -> IO a throwIfNeg = throwIf (< 0) -- |Like 'throwIfNeg', but discarding the result -- throwIfNeg_ :: (Ord a, Num a) => (a -> String) -> IO a -> IO () throwIfNeg_ = throwIf_ (< 0) -- |Guards against null pointers -- throwIfNull :: String -> IO (Ptr a) -> IO (Ptr a) throwIfNull = throwIf (== nullPtr) . const -- |Discard the return value of an 'IO' action -- void :: IO a -> IO () void act = act >> return () {-# DEPRECATED void "use 'Control.Monad.void' instead" #-} -- deprecated in 7.6