open Camlp4.PreCast;

let simplify =

  object

    inherit Ast.map as super;

    method expr e =

      match super#expr e with

      [ <:expr< $x$ + 0 >> | <:expr< 0 + $x$ >> -> x

      | x -> x ];

  end

in AstFilters.register_str_item_filter simplify#str_item;