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|
{-# 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
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
|
