sub say {
    print "$_\n" for @_;
}

sub debug {
    my ($msg,$lvl) = @_;
    say $msg if $lvl && $DEBUG{$lvl}
}

sub debug_lvl { map $DEBUG{$_} = 1, @_ }

##</code><code>##

debug "this...", LVL1;
...
debug "that ..", LVL3;

##</code><code>##

DEBUG and debug "text..", LVL1 ;