Ask HN: Facebook Comments on Wordpress. Help?

Here is the snipet provided by Facebook:

<script src="http://connect.facebook.net/en_US/all.js#xfbml=1"> </script><fb:comments href="YOUR_CANONICAL_URL"></fb:comments>

On Wordpress, any idea how to automate the canonical url portion so this can be placed in the single post editor of the theme?

Thanks