add init_grid func

src/vec2.ml

@@ -21,6 +21,12 @@ let ( + ) a b = Pair.map_same2 ( + ) a b
 let ( - ) a b = Pair.map_same2 ( - ) a b
 let ( = ) a b = Pair.equal ( = ) ( = ) a b
 
+let grid_vec2_of_idx ~width ~idx =
+  let y = idx / width in
+  let x = idx mod width in
+  x, y
+;;
+
 let at (grid : 'a grid) (point : t) =
   let x, y = point in
   if x >= 0 && x < grid.width && y >= 0 && y < grid.height
@@ -35,9 +41,14 @@ let at_e (grid : 'a grid) (point : t) =
 let find (grid : 'a grid) pred =
   let open Option.Infix in
   let* idx, item = Array.find_idx pred grid.items in
-  let y = idx / grid.width in
-  let x = idx mod grid.width in
-  Some ((x, y), item)
+  Some (grid_vec2_of_idx ~width:grid.width ~idx, item)
+;;
+
+let init_grid ~width ~height init =
+  { width
+  ; height
+  ; items = Array.init (width * height) (fun idx -> init @@ grid_vec2_of_idx ~width ~idx)
+  }
 ;;
 
 let parse_grid parse_char lines : 'a grid =

src/vec2.mli

@@ -14,6 +14,7 @@ val ( - ) : t -> t -> t
 val ( = ) : t -> t -> bool
 val at : 'a grid -> t -> 'a option
 val at_e : 'a grid -> t -> 'a
+val init_grid : width:int -> height:int -> (t -> 'a) -> 'a grid
 val parse_grid : (char -> 'a) -> string list -> 'a grid
 val find : 'a grid -> ('a -> bool) -> (t * 'a) option
 val iter_grid : 'a grid -> (t -> unit) -> unit