$app->add_event_handler(sub {
    ...
});

##</code><code>##

{
    my %paddle_move;
    my $key_joiner;

    BEGIN {
        $key_joiner = '~';
        %paddle_move = (
            SDL_KEYDOWN . $key_joiner . SDLK_UP, -2,
            SDL_KEYDOWN . $key_joiner . SDLK_DOWN, 2,
            SDL_KEYUP . $key_joiner . SDLK_UP, 0,
            SDL_KEYUP . $key_joiner . SDLK_DOWN, 0,
        );
    }

    $app->add_event_handler(sub {
        my $event = shift;
        my $paddle_key = $event->type . $key_joiner . $event->key_sym;

        if (exists $paddle_move{$paddle_key}) {
            $player1->{v_y} = $paddle_move{$paddle_key};
        }
    });
}