Cargo-cult some uses of atomicModifyIORef.

This seems to make no difference to performance, but I haven't looked at
memory usage.

src/System/Event/Array.hs

@@ -1,4 +1,4 @@
-{-# LANGUAGE CPP, ForeignFunctionInterface #-}
+{-# LANGUAGE BangPatterns, CPP, ForeignFunctionInterface #-}
 
 module System.Event.Array
     (
@@ -162,8 +162,10 @@ snoc (Array ref) e = do
     writeIORef ref (AC es len' cap)
 
 clear :: Storable a => Array a -> IO ()
-clear (Array ref) = atomicModifyIORef ref $ \(AC es _ cap) ->
-                    let !e = AC es 0 cap in (e, ())
+clear (Array ref) = do
+  !_ <- atomicModifyIORef ref $ \(AC es _ cap) ->
+        let e = AC es 0 cap in (e, e)
+  return ()
 
 forM_ :: Storable a => Array a -> (a -> IO ()) -> IO ()
 forM_ ary g = forHack ary g undefined

src/System/Event/Manager.hs

@@ -262,8 +262,8 @@ registerTimeout mgr ms cb = do
       now <- getCurrentTime
       let expTime = fromIntegral ms / 1000.0 + now
 
-      atomicModifyIORef (emTimeouts mgr) $ \q ->
-          let !q' = Q.insert key expTime cb q in (q', ())
+      !_ <- atomicModifyIORef (emTimeouts mgr) $ \q ->
+            let q' = Q.insert key expTime cb q in (q', q')
       wakeManager mgr
   return $! TK key
 
@@ -278,8 +278,8 @@ updateTimeout mgr (TK key) ms = do
     now <- getCurrentTime
     let expTime = fromIntegral ms / 1000.0 + now
 
-    atomicModifyIORef (emTimeouts mgr) $ \q ->
-        let !q' = Q.adjust (const expTime) key q in (q', ())
+    !_ <- atomicModifyIORef (emTimeouts mgr) $ \q ->
+          let q' = Q.adjust (const expTime) key q in (q', q')
     wakeManager mgr
 
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