-- | This module extends "Data.IORef" with operations forcing the value written to the IORef.
--   Some of these functions are available in later versions of GHC, but not all.
module Data.IORef.Extra(
    module Data.IORef,
    writeIORef', atomicWriteIORef',
    atomicModifyIORef_, atomicModifyIORef'_
    ) where

import Data.IORef
import Control.Exception


-- | Evaluates the value before calling 'writeIORef'.
writeIORef' :: IORef a -> a -> IO ()
writeIORef' :: forall a. IORef a -> a -> IO ()
writeIORef' IORef a
ref a
x = do
    a -> IO a
forall a. a -> IO a
evaluate a
x
    IORef a -> a -> IO ()
forall a. IORef a -> a -> IO ()
writeIORef IORef a
ref a
x

-- | Evaluates the value before calling 'atomicWriteIORef'.
atomicWriteIORef' :: IORef a -> a -> IO ()
atomicWriteIORef' :: forall a. IORef a -> a -> IO ()
atomicWriteIORef' IORef a
ref a
x = do
    a -> IO a
forall a. a -> IO a
evaluate a
x
    IORef a -> a -> IO ()
forall a. IORef a -> a -> IO ()
atomicWriteIORef IORef a
ref a
x


-- | Variant of 'atomicModifyIORef' which ignores the return value
atomicModifyIORef_ :: IORef a -> (a -> a) -> IO ()
atomicModifyIORef_ :: forall a. IORef a -> (a -> a) -> IO ()
atomicModifyIORef_ IORef a
r a -> a
f = IORef a -> (a -> (a, ())) -> IO ()
forall a b. IORef a -> (a -> (a, b)) -> IO b
atomicModifyIORef IORef a
r ((a -> (a, ())) -> IO ()) -> (a -> (a, ())) -> IO ()
forall a b. (a -> b) -> a -> b
$ \a
v -> (a -> a
f a
v, ())

-- | Variant of 'atomicModifyIORef'' which ignores the return value
atomicModifyIORef'_ :: IORef a -> (a -> a) -> IO ()
atomicModifyIORef'_ :: forall a. IORef a -> (a -> a) -> IO ()
atomicModifyIORef'_ IORef a
r a -> a
f = IORef a -> (a -> (a, ())) -> IO ()
forall a b. IORef a -> (a -> (a, b)) -> IO b
atomicModifyIORef' IORef a
r ((a -> (a, ())) -> IO ()) -> (a -> (a, ())) -> IO ()
forall a b. (a -> b) -> a -> b
$ \a
v -> (a -> a
f a
v, ())