sub myjoin (&@) {
    my $sub = shift;
    my $res = $_[0];
    for my $i (1 .. $#_) {
	$res .= $sub->($_[$i-1], $_[$i]) . $_[$i];
    }
    $res;
}

my @a = (':','',':','');
my $i=0;
print myjoin { $a[$i++] } 0,1,0,1; # Right now