Tag cloud for meta keywords how to?

Hello!

How to tag floud for meta keywords?

functions.php :

function kw_keywords(){
  if (is_home()) {
      echo '<meta name="keywords" content="example, example1" />'; //default keywords
  }
  if (is_single()){
      echo '<meta name="keywords" content="';
  }
  foreach((get_the_tags()) as $tags)
  if (is_single()){
  echo  $tags->tags_name . ', ';
  }
  if (is_single()){
  echo '" />';
  }
}

header.php :
<?php kw_keywords(); ?>

What could be the problem?

Thank you very much!