update Grid.%() operator to return option

src/grid.ml

@@ -36,7 +36,7 @@ let set_e grid point item =
   else failwith "point out of bounds!"
 ;;
 
-let ( .%() ) = at_e
+let ( .%() ) = at
 let ( .%()<- ) = set_e
 
 let find (grid : 'a t) pred =
@@ -88,7 +88,7 @@ let draw grid printer =
   let str = ref [] in
   iter grid (fun point ->
     let item = grid.%(point) in
-    let char = printer item in
+    let char = printer @@ Option.get_exn_or "iter is broken" item in
     str := !str @ [ char ];
     if point.x = grid.width - 1 then str := !str @ [ '\n' ]);
   String.of_list !str

src/grid.mli

@@ -3,7 +3,7 @@ type 'a t [@@deriving show]
 val at : 'a t -> Vec2.t -> 'a option
 val at_e : 'a t -> Vec2.t -> 'a
 val set_e : 'a t -> Vec2.t -> 'a -> unit
-val ( .%() ) : 'a t -> Vec2.t -> 'a
+val ( .%() ) : 'a t -> Vec2.t -> 'a option
 val ( .%()<- ) : 'a t -> Vec2.t -> 'a -> unit
 val init : width:int -> height:int -> (Vec2.t -> 'a) -> 'a t
 val of_lines : (char -> 'a) -> string list -> 'a t