feat(list): add sorted_mem

src/core/CCList.ml

@@ -797,6 +797,19 @@ let is_sorted ~cmp l =
     is_sorted ~cmp:CCInt.compare (List.sort Stdlib.compare l))
 *)
 
+let rec sorted_mem ~cmp x l = match l with
+  | [] -> false
+  | y :: tail ->
+    match cmp x y with
+      | 0 -> true
+      | n when n<0 -> false
+      | _ -> (sorted_mem[@tailcall]) ~cmp x tail
+
+(*$Q
+  Q.(pair small_int (list small_int)) (fun (x,l) -> \
+    sorted_mem ~cmp:CCInt.compare x (List.sort CCInt.compare l) = mem ~eq:CCInt.equal x l)
+*)
+
 let sorted_insert ~cmp ?(uniq=false) x l =
   let rec aux cmp uniq x left l = match l with
     | [] -> List.rev_append left [x]

src/core/CCList.mli

@@ -523,6 +523,10 @@ val is_sorted : cmp:('a -> 'a -> int) -> 'a list -> bool
     @param cmp the comparison function.
     @since 0.17 *)
 
+val sorted_mem : cmp:('a -> 'a -> int) -> 'a -> 'a list -> bool
+(** Suppose the list [l] is sorted. [sorted_mem x l] is [true] iff [x] is equal to an element of [l].
+    @since NEXT_RELEASE *)
+
 val sorted_insert : cmp:('a -> 'a -> int) -> ?uniq:bool -> 'a -> 'a list -> 'a list
 (** [sorted_insert ~cmp ?uniq x l] inserts [x] into [l] such that, if [l] was sorted,
     then [sorted_insert x l] is sorted too.

src/core/CCListLabels.mli

@@ -526,6 +526,10 @@ val is_sorted : cmp:(('a -> 'a -> int) [@keep_label]) -> 'a list -> bool
     @param cmp the comparison function.
     @since 0.17 *)
 
+val sorted_mem : cmp:(('a -> 'a -> int) [@keep_label]) -> 'a -> 'a list -> bool
+(** Suppose the list [l] is sorted. [sorted_mem x l] is [true] iff [x] is equal to an element of [l].
+    @since NEXT_RELEASE *)
+
 val sorted_insert : cmp:(('a -> 'a -> int) [@keep_label]) -> ?uniq:bool -> 'a -> 'a list -> 'a list
 (** [sorted_insert ~cmp ?uniq x l] inserts [x] into [l] such that, if [l] was sorted,
     then [sorted_insert x l] is sorted too.