feat: add monoid_product to Array and Vector

src/core/CCArray.ml

@@ -268,6 +268,19 @@ let flat_map f a =
   a' = [| 1; 2; 3; 4; 5; 6 |]
 *)
 
+let monoid_product f a1 a2 =
+  let na1 = length a1 in
+  init (na1 * length a2)
+    (fun i_prod ->
+       let i = i_prod mod na1 in
+       let j = i_prod / na1 in
+       f a1.(i) a2.(j))
+
+(*$= & ~cmp:(=) ~printer:Q.Print.(array int)
+  [| 11; 12; 21; 22 |] (sorted CCInt.compare @@ monoid_product (+) [| 10; 20 |] [| 1; 2 |])
+  [| 11; 12; 13; 14 |] (sorted CCInt.compare @@ monoid_product (+) [| 10 |] [| 1; 2; 3; 4 |])
+*)
+
 let rec _lookup_rec ~cmp k a i j =
   if i>j then raise Not_found
   else if i=j

src/core/CCArray.mli

@@ -298,6 +298,10 @@ val filter_map : ('a -> 'b option) -> 'a t -> 'b t
     of all elements [bi] such as [f ai = Some bi]. When [f] returns [None], the corresponding
     element of [a] is discarded. *)
 
+val monoid_product : ('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t
+(** All combinaisons of tuples from the two arrays are passed to the function
+    @since NEXT_RELEASE *)
+
 val flat_map : ('a -> 'b t) -> 'a t -> 'b array
 (** [flat_map f a] transforms each element of [a] into an array, then flattens. *)
 

src/core/CCArrayLabels.mli

@@ -302,6 +302,10 @@ val filter_map : f:('a -> 'b option) -> 'a t -> 'b t
 val flat_map : f:('a -> 'b t) -> 'a t -> 'b array
 (** [flat_map ~f a] transforms each element of [a] into an array, then flattens. *)
 
+val monoid_product : f:('a -> 'b -> 'c) -> 'a t -> 'b t -> 'c t
+(** All combinaisons of tuples from the two arrays are passed to the function
+    @since NEXT_RELEASE *)
+
 val (>>=) : 'a t -> ('a -> 'b t) -> 'b t
 (** [a >>= f] is the infix version of {!flat_map}. *)
 

src/core/CCVector.ml

@@ -753,6 +753,21 @@ let flat_map_list f v =
     v;
   v'
 
+let monoid_product f a1 a2 : _ t =
+  let na1 = a1.size in
+  init (na1 * a2.size)
+    (fun i_prod ->
+       let i = i_prod mod na1 in
+       let j = i_prod / na1 in
+       f a1.vec.(i) a2.vec.(j))
+
+(*$= & ~cmp:(=) ~printer:Q.Print.(list int)
+  [ 11; 12; 21; 22 ] (List.sort CCInt.compare @@ \
+                      to_list @@ monoid_product (+) (of_list [10; 20]) (of_list [1; 2]))
+  [ 11; 12; 13; 14 ] (List.sort CCInt.compare @@ \
+                      to_list @@ monoid_product (+) (of_list [10]) (of_list [1; 2; 3; 4]))
+*)
+
 let (>>=) x f = flat_map f x
 
 let (>|=) x f = map f x

src/core/CCVector.mli

@@ -198,6 +198,10 @@ val flat_map_list : ('a -> 'b list) -> ('a,_) t -> ('b, 'mut) t
     intermediate collections.
     @since 0.14 *)
 
+val monoid_product : ('a -> 'b -> 'c) -> ('a,_) t -> ('b,_) t -> ('c,_) t
+(** All combinaisons of tuples from the two vectors are passed to the function.
+    @since NEXT_RELEASE *)
+
 val (>>=) : ('a,_) t -> ('a -> ('b,_) t) -> ('b, 'mut) t
 (** Infix version of {!flat_map}. *)