Stdlib: add List.split_n

src/lib_stdlib/tzList.ml

@@ -69,13 +69,15 @@ let rec remove nb = function
 
 let rec repeat n x = if n <= 0 then [] else x :: repeat (pred n) x
 
-let take_n_unsorted n l =
+let split_n n l =
   let rec loop acc n = function
-    | [] -> l
-    | _ when n <= 0 -> List.rev acc
+    | [] -> l, []
+    | rem when n <= 0 -> List.rev acc, rem
     | x :: xs -> loop (x :: acc) (pred n) xs in
   loop [] n l
 
+let take_n_unsorted n l = fst (split_n n l)
+
 module Bounded(E: Set.OrderedType) : sig
 
   type t

src/lib_stdlib/tzList.mli

@@ -23,6 +23,8 @@ val product : 'a list -> 'b list -> ('a * 'b) list
     is provided, it returns the [n] greatest element of [l]. *)
 val take_n: ?compare:('a -> 'a -> int) -> int -> 'a list -> 'a list
 
+val split_n: int -> 'a list -> 'a list * 'a list
+
 (** Bounded sequence: keep only the [n] greatest elements. *)
 module Bounded(E: Set.OrderedType) : sig
   type t