Two more things: I think that tails and inits may be more complex than necessary. When I see partial pattern matches like in zipDigit/zipNode, I worry that the hidden invariants are both extra complexity for a human reader and a missed opportunity for the compiler. I think you're doing it because you want the two traversals to go in opposite directions, so that you don't need to start with the total size of the prefix or suffix, but it turns out that you're computing these anyway. So you might as well combine the pairs of traversals in each case. The names of the sequential search functions: takeWhile :: (a -> Bool) -> Seq a -> Seq a takeWhileEnd :: (a -> Bool) -> Seq a -> Seq a dropWhile :: (a -> Bool) -> Seq a -> Seq a dropWhileEnd :: (a -> Bool) -> Seq a -> Seq a span :: (a -> Bool) -> Seq a -> (Seq a, Seq a) spanEnd :: (a -> Bool) -> Seq a -> (Seq a, Seq a) break :: (a -> Bool) -> Seq a -> (Seq a, Seq a) breakEnd :: (a -> Bool) -> Seq a -> (Seq a, Seq a) elemIndex :: Eq a => a -> Seq a -> Maybe Int elemIndices :: Eq a => a -> Seq a -> [Int] elemLastIndex :: Eq a => a -> Seq a -> Maybe Ind elemIndicesDesc :: Eq a => a -> Seq a -> [Int] findIndex :: (a -> Bool) -> Seq a -> Maybe Int findIndices :: (a -> Bool) -> Seq a -> [Int] findLastIndex :: (a -> Bool) -> Seq a -> Maybe Int findIndicesDesc :: (a -> Bool) -> Seq a -> [Int] conflict with the symmetrical view of sequences elsewhere in the interface. Sequences are viewed as having left and right ends, not front and back or first and last. (Of course the existing functions take and drop have similar issues, but at least they didn't involve new names.) So I'd prefer L and R variants of each (perhaps with spanl/spanr and breakl/breakr for consistency with other similar names).