8.20 Extended indexing operators

(Introduced in 4.06)

This extension provides syntactic sugar for getting and setting elementsfor user-defined indexed types. For instance, we can define python-likedictionaries with

 module Dict = struct
 include Hashtbl
 let ( .%{} ) tabl index = find tabl index
 let ( .%{}<- ) tabl index value = add tabl index value
 end
 let dict =
   let dict = Dict.create 10 in
   let () =
     dict.Dict.%{"one"} <- 1;
     let open Dict in
     dict.%{"two"} <- 2 in
   dict
 

 dict.Dict.%{"one"};;
- : int = 1

 let open Dict in dict.%{"two"};;
- : int = 2