Data.Sequence offers deleteAt :: Int -> Seq a -> Seq a which deletes the element at the given index. Today, I ran into a situation where I wanted to know what was deleted. deleteLookup :: Int -> Seq a -> Maybe (a, Seq a) The closest thing I can find in `containers` is in Data.Map: updateLookupWithKey :: Ord k => (k -> a -> Maybe a) -> k -> Map k a -> (Maybe a,Map k a) Unfortunately, that function is ugly and strange. A better one, whose name I can't guess at the moment: flabbergast :: (a -> (b, Maybe a)) -> Int -> Seq a -> Maybe (b, Seq a) where a Nothing result means the index was out of bounds. There's also a potential flabbergastF :: Functor f => (a -> f (Maybe a)) -> Int -> Seq a -> Maybe (f (Seq a)) I'm not sure if flabbergast can be made as fast as deleteLookup, so it's possible we may want both. Any opinions?