use feature qw( state );
   use Type::Params qw( compile_named_oo );
   use Types::Standard qw( Num );
   
   sub add_numbers {
      state $signature = compile_named_oo(
         { head => [ Any ] },
         'x' => Num,
         'y' => Num,
      );
      my ( $self, $arg ) = $signature->( @_ );
      
      return $arg->x + $arg->y;
   }