# subroutine name: copy_struct
# Input: reference to Perl structure (without loops!!!)
# Returns: reference to copy of structure
sub copy_struct {
	my ($struct) = @_;
	my $res;
	if (ref($struct) eq "SCALAR") {
		my $copy=$$struct;
		$res=\$copy;
	} elsif (ref($struct) eq "ARRAY") {
		my @copy=();
		foreach (@{$struct}) { push(@copy,&copy_struct($_)) };
		$res=\@copy;
	} elsif (ref($struct) eq "HASH") {
		my %copy=();
		foreach (keys %{$struct}) { $copy{$_}=&copy_struct($struct->{$_}) };
		$res=\%copy;
	} elsif (ref($struct) eq "REF") {
		my $copy=&copy_struct($$struct);
		$res=\$copy;
	} else {
		$res=$struct;
	}
	return $res;
}