add CCList.take_last

src/core/CCList.ml

@@ -823,6 +823,20 @@ let hd_tl = function
 
 let take_drop n l = take n l, drop n l
 
+let rec take_last = function
+  | [] -> failwith "take_last"
+  | [ x ] -> [], x
+  | hd :: tl ->
+    let tl, lt = take_last tl in
+    hd :: tl, lt
+
+let rec take_last_opt = function
+  | [] -> [], None
+  | [ x ] -> [], Some x
+  | hd :: tl ->
+    let tl, lt = take_last_opt tl in
+    hd :: tl, lt
+
 let sublists_of_len ?(last = fun _ -> None) ?offset n l =
   if n < 1 then invalid_arg "sublists_of_len: n must be > 0";
   let offset =

src/core/CCList.mli

@@ -414,6 +414,12 @@ val take_drop_while : ('a -> bool) -> 'a t -> 'a t * 'a t
     @since 1.2, but only
     @since 2.2 with labels *)
 
+val take_last : 'a t -> 'a t * 'a
+(** [take_last l] = (tl l, last l). *)
+
+val take_last_opt : 'a t -> 'a t * 'a option
+(** [take_last l] = (tl l, last_opt l). *)
+
 val last : int -> 'a t -> 'a t
 (** [last n l] takes the last [n] elements of [l] (or less if
     [l] doesn't have that many elements). *)

src/core/CCListLabels.mli

@@ -447,6 +447,12 @@ val take_drop_while : f:('a -> bool) -> 'a t -> 'a t * 'a t
     @since 1.2, but only
     @since 2.2 with labels *)
 
+val take_last : 'a t -> 'a t * 'a
+(** [take_last l] = (tl l, last l). *)
+
+val take_last_opt : 'a t -> 'a t * 'a option
+(** [take_last l] = (tl l, last_opt l). *)
+
 val last : int -> 'a t -> 'a t
 (** [last n l] takes the last [n] elements of [l] (or less if
     [l] doesn't have that many elements). *)

tests/core/t_list.ml

@@ -807,6 +807,13 @@ t @@ fun () -> take_while (fun x -> x <> 0) [ 0; 1; 2; 3 ] = [];;
 t @@ fun () -> take_while (fun _ -> true) [] = [];;
 t @@ fun () -> take_while (fun _ -> true) (1 -- 10) = 1 -- 10;;
 t @@ fun () -> take_while (fun _ -> true) (1 -- 300_000) = 1 -- 300_000;;
+t @@ fun () -> take_last [ 1 ] = ([], 1);;
+t @@ fun () -> take_last [ 1; 2; 3; 4; 5 ] = ([ 1; 2; 3; 4 ], 5);;
+t @@ fun () -> take_last (1 -- 10_000) = (1 -- 9_999, 10_000);;
+t @@ fun () -> take_last_opt [] = ([], None);;
+t @@ fun () -> take_last_opt [ 1 ] = ([], Some 1);;
+t @@ fun () -> take_last_opt [ 1; 2; 3; 4; 5 ] = ([ 1; 2; 3; 4 ], Some 5);;
+t @@ fun () -> take_last_opt (1 -- 10_000) = (1 -- 9_999, Some 10_000);;
 
 q
   Q.(pair (fun1 Observable.int bool) (list small_int))