Time::Piece::Month（来月を求める）

 use Time::Piece;
 use TIme::Piece::Month;
 
 my $this_month  = Time::Piece::Month->new( Time::Piece->new() );
 my $month200201 = Time::Piece::Month->new("2002-01-03");
 
 my @next_month_dates = $this_month->next_month->dates();
 my $next_month_1st   = [ $this_month->next_month->dates() ]->[0];
 
 say $next_month_1st->ymd; # "20XX-XX-01"