    {-# 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 :: forall a. (a -> Bool) -> (a -> String) -> IO a -> IO a
    throwIf a -> Bool
    pred a -> String
    msgfct IO a
    act  =
      do
        a
    res <- IO a
    act
        (if a -> Bool
    pred a
    res then IOError -> IO a
    forall a. IOError -> IO a
    ioError (IOError -> IO a) -> (a -> IOError) -> a -> IO a
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> IOError
    userError (String -> IOError) -> (a -> String) -> a -> IOError
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . a -> String
    msgfct else a -> IO a
    forall (m :: * -> *) a. Monad m => a -> m a
    return) a
    res

    -- |Like 'throwIf', but discarding the result
    --
    throwIf_                 :: (a -> Bool) -> (a -> String) -> IO a -> IO ()
    throwIf_ :: forall a. (a -> Bool) -> (a -> String) -> IO a -> IO ()
    throwIf_ a -> Bool
    pred a -> String
    msgfct IO a
    act  = IO a -> IO ()
    forall a. IO a -> IO ()
    void (IO a -> IO ()) -> IO a -> IO ()
    forall a b. (a -> b) -> a -> b
    $ (a -> Bool) -> (a -> String) -> IO a -> IO a
    forall a. (a -> Bool) -> (a -> String) -> IO a -> IO a
    throwIf a -> Bool
    pred a -> String
    msgfct IO a
    act

    -- |Guards against negative result values
    --
    throwIfNeg :: (Ord a, Num a) => (a -> String) -> IO a -> IO a
    throwIfNeg :: forall a. (Ord a, Num a) => (a -> String) -> IO a -> IO a
    throwIfNeg  = (a -> Bool) -> (a -> String) -> IO a -> IO a
    forall a. (a -> Bool) -> (a -> String) -> IO a -> IO a
    throwIf (a -> a -> Bool
    forall a. Ord a => a -> a -> Bool
    < a
    0)

    -- |Like 'throwIfNeg', but discarding the result
    --
    throwIfNeg_ :: (Ord a, Num a) => (a -> String) -> IO a -> IO ()
    throwIfNeg_ :: forall a. (Ord a, Num a) => (a -> String) -> IO a -> IO ()
    throwIfNeg_  = (a -> Bool) -> (a -> String) -> IO a -> IO ()
    forall a. (a -> Bool) -> (a -> String) -> IO a -> IO ()
    throwIf_ (a -> a -> Bool
    forall a. Ord a => a -> a -> Bool
    < a
    0)

    -- |Guards against null pointers
    --
    throwIfNull :: String -> IO (Ptr a) -> IO (Ptr a)
    throwIfNull :: forall a. String -> IO (Ptr a) -> IO (Ptr a)
    throwIfNull  = (Ptr a -> Bool) -> (Ptr a -> String) -> IO (Ptr a) -> IO (Ptr a)
    forall a. (a -> Bool) -> (a -> String) -> IO a -> IO a
    throwIf (Ptr a -> Ptr a -> Bool
    forall a. Eq a => a -> a -> Bool
    == Ptr a
    forall a. Ptr a
    nullPtr) ((Ptr a -> String) -> IO (Ptr a) -> IO (Ptr a))
    -> (String -> Ptr a -> String)
    -> String
    -> IO (Ptr a)
    -> IO (Ptr a)
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> Ptr a -> String
    forall a b. a -> b -> a
    const

    -- |Discard the return value of an 'IO' action
    --
    void     :: IO a -> IO ()
    void :: forall a. IO a -> IO ()
    void IO a
    act  = IO a
    act IO a -> IO () -> IO ()
    forall (m :: * -> *) a b. Monad m => m a -> m b -> m b
    >> () -> IO ()
    forall (m :: * -> *) a. Monad m => a -> m a
    return ()
    {-# DEPRECATED void "use 'Control.Monad.void' instead" #-} -- deprecated in 7.6