Array.traverse{ST,IO} are untested

[sjakobi]

…says stack test --coverage (#270).

unordered-containers/Data/HashMap/Array.hs

Lines 575 to 619 in 964edca

	-- Traversing in ST, we don't need to get fancy; we
	-- can just do it directly.
	traverseST :: (a -> ST s b) -> Array a -> ST s (Array b)
	traverseST f = \ ary0 ->
	let
	!len = length ary0
	go k !mary
	| k == len = return mary
	| otherwise = do
	x <- indexM ary0 k
	y <- f x
	write mary k y
	go (k + 1) mary
	in new_ len >>= (go 0 >=> unsafeFreeze)
	{-# INLINE traverseST #-}
	traverseIO :: (a -> IO b) -> Array a -> IO (Array b)
	traverseIO f = \ ary0 ->
	let
	!len = length ary0
	go k !mary
	| k == len = return mary
	| otherwise = do
	x <- stToIO $ indexM ary0 k
	y <- f x
	stToIO $ write mary k y
	go (k + 1) mary
	in stToIO (new_ len) >>= (go 0 >=> stToIO . unsafeFreeze)
	{-# INLINE traverseIO #-}
	-- Why don't we have similar RULES for traverse'? The efficient
	-- way to traverse strictly in IO or ST is to force results as
	-- they come in, which leads to different semantics. In particular,
	-- we need to ensure that
	--
	-- traverse' (\x -> print x *> pure undefined) xs
	--
	-- will actually print all the values and then return undefined.
	-- We could add a strict mapMWithIndex, operating in an arbitrary
	-- Monad, that supported such rules, but we don't have that right now.
	{-# RULES
	"traverse/ST" forall f. traverse f = traverseST f
	"traverse/IO" forall f. traverse f = traverseIO f
	#-}