Hi all, Please have a look at http://moonpatio.com/fastcgi/hpaste.fcgi/view?id=2575#a2575 I wanted to use the typesystem to mandate businesslogic (in this case w3c validation rules). Thanks to some helpful people in #haskell I learned a bit about phantom types. Please let me know if I implemented them correctly. Also this little experiment raises some questions: The code becomes very verbose if there are more elements added or more rules to check. Since repetitive code can be a source of error, and hellish to maintain, I would like to know if there's some way to get this generated, or maybe there's some meta-programming stuff I don't know about. Another thing I can't figure out yet is how to do more advanced validation rules like "an html element cannot have 2 head sections", or (made up) "a span element isn't allowed to be a child(any level deep) of a p element". I think this would ask for an exponentially growing number of strange types and classes. Am I right? Just to be clear: this is just some practice to use the typesystem. I'm well aware that just using runtime validation checks will be a lot easier and clearer in most cases. Thanks, Mathijs