add CCString.{lines,unlines,concat_gen}

src/core/CCString.cppo.ml

@@ -263,6 +263,20 @@ let of_array a =
 let to_array s =
   Array.init (String.length s) (fun i -> s.[i])
 
+let lines s = Split.gen_cpy ~by:"\n" s
+
+let concat_gen ~sep g =
+  let b = Buffer.create 256 in
+  let rec aux ~first () = match g () with
+    | None -> Buffer.contents b
+    | Some s ->
+      if not first then Buffer.add_string b sep;
+      Buffer.add_string b s;
+      aux ~first:false ()
+  in aux ~first:true ()
+
+let unlines g = concat_gen ~sep:"\n" g
+
 let pp buf s =
   Buffer.add_char buf '"';
   Buffer.add_string buf s;

src/core/CCString.mli

@@ -113,6 +113,22 @@ val suffix : suf:string -> string -> bool
   not (suffix ~suf:"abcd" "cd")
 *)
 
+val lines : string -> string gen
+(** [lines s] returns a generator of the lines of [s] (splits along '\n')
+    @since NEXT_RELEASE *)
+
+val concat_gen : sep:string -> string gen -> string
+(** [concat_gen ~sep g] concatenates all strings of [g], separated with [sep].
+    @since NEXT_RELEASE *)
+
+val unlines : string gen -> string
+(** [unlines g] concatenates all strings of [g], separated with '\n'
+    @since NEXT_RELEASE *)
+
+(*$Q
+  Q.printable_string (fun s -> unlines (lines s) = s)
+*)
+
 include S with type t := string
 
 (** {2 Splitting} *)