Suspicious lack of bang patterns in intersectionCollisions and searchSwap

[sjakobi]

I'm not sure whether this leads to any unwanted laziness or reboxing, but I'd feel more comfortable if some bang patterns would simply rule out such issues.

unordered-containers/Data/HashMap/Internal.hs

Lines 1888 to 1933 in 19674b5

	intersectionCollisions :: Eq k => (k -> v1 -> v2 -> (# v3 #)) -> Hash -> Hash -> A.Array (Leaf k v1) -> A.Array (Leaf k v2) -> HashMap k v3
	intersectionCollisions f h1 h2 ary1 ary2
	| h1 == h2 = runST $ do
	mary2 <- A.thaw ary2 0 $ A.length ary2
	mary <- A.new_ $ min (A.length ary1) (A.length ary2)
	let go i j
	| i >= A.length ary1 || j >= A.lengthM mary2 = pure j
	| otherwise = do
	L k1 v1 <- A.indexM ary1 i
	searchSwap k1 j mary2 >>= \case
	Just (L _k2 v2) -> do
	let !(# v3 #) = f k1 v1 v2
	A.write mary j $ L k1 v3
	go (i + 1) (j + 1)
	Nothing -> do
	go (i + 1) j
	len <- go 0 0
	case len of
	0 -> pure Empty
	1 -> Leaf h1 <$> A.read mary 0
	_ -> Collision h1 <$> (A.unsafeFreeze =<< A.shrink mary len)
	| otherwise = Empty
	{-# INLINE intersectionCollisions #-}
	-- | Say we have
	-- @
	-- 1 2 3 4
	-- @
	-- and we search for @3@. Then we can mutate the array to
	-- @
	-- undefined 2 1 4
	-- @
	-- We don't actually need to write undefined, we just have to make sure that the next search starts 1 after the current one.
	searchSwap :: Eq k => k -> Int -> A.MArray s (Leaf k v) -> ST s (Maybe (Leaf k v))
	searchSwap toFind start = go start toFind start
	where
	go i0 k i mary
	| i >= A.lengthM mary = pure Nothing
	| otherwise = do
	l@(L k' _v) <- A.read mary i
	if k == k'
	then do
	A.write mary i =<< A.read mary i0
	pure $ Just l
	else go i0 k (i + 1) mary
	{-# INLINE searchSwap #-}

The searchSwap variant being added in #435 should get similar bang patterns.