[feature] libbase: choose_opt in Maps and Sets

Same as choose, but giving an option instead of an exception on empty map/set

libbase/baseMap.ml

@@ -576,6 +576,10 @@ struct
               add k v acc
          ) map1 empty
 
+  let rec choose_opt = function
+    | Empty -> None
+    | Node(_, k, v, _r, _) -> Some (k, v)
+
   let from_sorted_array keys vals =
     let len_keys = Array.length keys in
     let len_vals = Array.length vals in

libbase/baseMapSig.ml

@@ -80,6 +80,11 @@ sig
      @raise Not_found on the empty list
   *)
   val choose : 'a t -> (key * 'a)
+
+  (**
+     Returns an arbitrary element of the set if it is not_empty, or null
+  *)
+  val choose_opt : 'a t -> (key * 'a) option
   val map : ('a -> 'b) -> 'a t -> 'b t
   val mapi : (key -> 'a -> 'b) -> 'a t -> 'b t
   val fold_map : (key -> 'a -> 'c -> 'c * 'b) -> 'a t -> 'c -> 'c * 'b t

libbase/baseSet.ml

@@ -321,6 +321,10 @@ struct
 
   let choose = min_elt
 
+  let rec choose_opt = function
+    | Empty -> None
+    | Node (_, v, _r, _) -> Some v
+
   let complete_join big small =
     fold add small big
 

libbase/baseSetSig.ml

@@ -62,6 +62,11 @@ sig
      @raise Not_found on the empty set
   *)
   val choose : t -> elt
+
+  (**
+     Returns an arbitrary element of the set if it is not empty
+  *)
+  val choose_opt : t -> elt option
   val split : elt -> t -> t * bool * t
   val draw : t -> elt * t
   val size : t -> int

libbase/intMap.ml

@@ -338,6 +338,9 @@ let min t = ordertop min t
 *)
 let choose = min
 
+let choose_opt t =
+  try Some (choose t) with | Not_found -> None
+
 let rec max t = match t with
   | Br (_,_m,_tl,tr) -> max tr
   | Lf (k,v) -> k,v

libbase/intSet.ml

@@ -70,6 +70,12 @@ let diff set set' = filter (fun x -> not (mem x set')) set
 let subset (set:t) (set':t) = for_all (fun x -> mem x set') set
 
 let choose = min_elt
+
+let choose_opt (set:t) =
+  match IntMap.choose_opt set with
+  | None -> None
+  | Some (a, _) -> Some a
+
 let split int set =
   fold
     (fun i (inf, b, sup) ->