use feature qw( state );
   use Type::Params qw( signature );
   use Types::Standard qw( Num );
   
   sub add_numbers {
      state $signature = signature(
         method     => 0,
         positional => [ Num, Num ],
      );
      my ( $x, $y ) = $signature->( @_ );
      
      return $x + $y;
   }