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{-# LANGUAGE CPP #-}
module Network.Wai.Handler.Warp.IORef (
module Data.IORef
#if !MIN_VERSION_base(4,6,0)
, atomicModifyIORef'
#endif
) where
import Data.IORef
#if !MIN_VERSION_base(4,6,0)
-- | Strict version of 'atomicModifyIORef'. This forces both the value stored
-- in the 'IORef' as well as the value returned.
atomicModifyIORef' :: IORef a -> (a -> (a,b)) -> IO b
atomicModifyIORef' ref f = do
c <- atomicModifyIORef ref
(\x -> let (a, b) = f x -- Lazy application of "f"
in (a, a `seq` b)) -- Lazy application of "seq"
-- The following forces "a `seq` b", so it also forces "f x".
c `seq` return c
#endif
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