add CCSeq.{zip_i,of_string}

src/core/CCSeq.ml

@@ -356,6 +356,17 @@ let unzip l =
     let l = of_list l in let a, b = unzip l in equal (=) l (zip a b))
 *)
 
+let zip_i seq =
+  let rec loop i seq () = match seq() with
+    | Nil -> Nil
+    | Cons (x,tl) -> Cons ((i,x), loop (i+1) tl)
+  in
+  loop 0 seq
+
+(*$=
+  [0,'a'; 1, 'b'; 2, 'c'] (of_string "abcde" |> zip_i |> take 3 |> to_list)
+*)
+
 (** {2 Implementations} *)
 
 let return x () = Cons (x, nil)
@@ -394,6 +405,13 @@ let of_array a =
   in
   aux a 0
 
+let of_string s =
+  let rec aux s i () =
+    if i=String.length s then Nil
+    else Cons (String.get s i, aux s (i+1))
+  in
+  aux s 0
+
 let to_array l =
   (* We contruct the length and list of seq elements (in reverse) in one pass *)
   let len, ls = fold_left (fun (i, acc) x -> (i + 1, x :: acc)) (0, []) l in

src/core/CCSeq.mli

@@ -166,6 +166,11 @@ val zip : 'a t -> 'b t -> ('a * 'b) t
 val unzip : ('a * 'b) t -> 'a t * 'b t
 (** Split each tuple in the list. *)
 
+val zip_i : 'a t -> (int * 'a) t
+(** [zip_i seq] zips the index of each element with the element itself.
+    @since NEXT
+*)
+
 (** {2 Misc} *)
 
 val sort : cmp:'a ord -> 'a t -> 'a t
@@ -254,6 +259,10 @@ val to_gen : 'a t -> 'a gen
 val of_gen : 'a gen -> 'a t
 (** [of_gen g] consumes the generator and caches intermediate results. *)
 
+val of_string : string -> char t
+(** Iterate on characters.
+    @since NEXT_RELEASE *)
+
 (** {2 IO} *)
 
 val pp : ?pp_start:unit printer -> ?pp_stop:unit printer -> ?pp_sep:unit printer ->