diff --git a/seq.ml b/seq.ml
index cc8cc42..4be218a 100644
--- a/seq.ml
+++ b/seq.ml
@@ -1,33 +1,34 @@
 include Stdlib.Seq
 
-type 'a span = Empty_seq | Span of 'a list * 'a t
+let for_all p = fold_left (fun acc x -> acc && p x) true
+let exists  p = fold_left (fun acc x -> acc || p x) false
 
 let span' p seq =
   let rec go acc = function
     | Nil -> begin
         match acc with
-        | []   -> Empty_seq
-        | _::_ -> Span (List.rev acc, empty)
+        | []   -> None
+        | _::_ -> Some (List.rev acc, empty)
       end
     | Cons (x, xs) ->
         if p x then
           go (x :: acc) (xs ())
         else
-          Span (List.rev acc, cons x xs) in
+          Some (List.rev acc, cons x xs) in
   go [] (seq ())
 
 let%test_module _ = (module struct
   let (@=) sp (l2, s2) =
     match sp with
-    | Span (l1, s1) -> l1 = l2 && List.of_seq s1 = s2
-    | Empty_seq     -> false
+    | Some (l1, s1) -> l1 = l2 && List.of_seq s1 = s2
+    | None          -> false
 
   let%test _ =
     span' (fun x -> x < 4) (List.to_seq [1;2;3;4;5;6;7]) @=
       ([1;2;3], [4;5;6;7])
 
   let%test _ =
-    span' (fun _ -> true) (List.to_seq []) = Empty_seq
+    span' (fun _ -> true) (List.to_seq []) = None
 
   let%test _ =
     span' (fun x -> x < 0) (List.to_seq [1;2;3;4;5;6;7]) @=
@@ -36,9 +37,7 @@ end)
 
 let break' p = span' (Fun.negate p)
 
-let from_span = function
-  | Empty_seq       -> [], empty
-  | Span (lst, seq) -> lst, seq
+let from_span = Option.value ~default:([], empty)
 
 let span p seq = from_span (span' p seq)
 let break p seq = from_span (break' p seq)
@@ -51,12 +50,13 @@ let rec drop_while p seq =
       if p x then drop_while p xs else cons x xs
 
 let chunks ~sep =
-  unfold (fun seq ->
-    match break' sep seq with
-    | Empty_seq -> None
-    | Span (lst, seq) -> Some (lst, drop_while sep seq))
+  let drop_snd (lst, seq) = lst, drop_while sep seq in
+  unfold (fun seq -> break' sep seq |> Option.map drop_snd)
 
-let line_chunks' = chunks ~sep:(fun s -> s = "")
+let is_space c = c = ' ' || c = '\t' || c = '\n'
+let all_space str = String.to_seq str |> for_all is_space
+
+let line_chunks' = chunks ~sep:all_space
 let line_chunks ?(join=" ") seq = map (String.concat join) (line_chunks' seq)
 
 let%test_module _ = (module struct
diff --git a/seq.mli b/seq.mli
index d8c584f..060a18b 100644
--- a/seq.mli
+++ b/seq.mli
@@ -1,9 +1,10 @@
 include module type of Stdlib.Seq
 
-type 'a span = Empty_seq | Span of 'a list * 'a t
+val for_all: ('a -> bool) -> 'a t -> bool
+val exists: ('a -> bool) -> 'a t -> bool
 
-val span': ('a -> bool) -> 'a t -> 'a span
-val break': ('a -> bool) -> 'a t -> 'a span
+val span': ('a -> bool) -> 'a t -> ('a list * 'a t) option
+val break': ('a -> bool) -> 'a t -> ('a list * 'a t) option
 
 val span: ('a -> bool) -> 'a t -> 'a list * 'a t
 val break: ('a -> bool) -> 'a t -> 'a list * 'a t