Etwas

my @mission_list;

add_children( \%root );

sub add_children {
    my ( $mission ) = @_;
    
    for my $i ( 0 .. $#mission_list ) {
	[...]
            if ( $#{$mission_list[$i]{reqs}} < 0 ) {
                delete $mission_list[$i];
                @mission_list = grep { defined } @mission_list;
                print "$#mission_list\n\n";
            }
	[...]
    }
    
    for my $i ( 0 .. $#{$$mission{children}} ) {
        add_children ( $$mission{children}[$i] );
    }
}