anchor.diff:  +getHomeR+ function was able to return +Html+: Yesod knows how to convert it to
   +TypedContent+, and from there it can be converted into a +WAI+ response.
   
  -=== HasContentType and representations
  +==== HasContentType and representations
   
   This typeclass approach allows for one other nice abstraction. For many types, the type system itself lets us know what the content-type for the content should be. For example, +Html+ will always be served with a +text/html+ content-type.
   
  
positive.code: messages, take advantage of the widget system, so by using widgets, you get a
  consistent feel throughout your site.
  
  == Forms
  
  FIXME
  
  == Persistent
  
  FIXME
  
  == WAI middlewares
  
  FIXME
  
  
negative.code: 
  There are many aspects of WAI we haven't covered here. One important topic is WAI middlewares, which we'll cover towards the end of this chapter. We also haven't inspected request bodies at all. But for the purposes of understanding Yesod, we've covered enough for the moment.
  
  === What about Yesod?
  
  In all our excitement about WAI and Warp, we still haven't seen anything about Yesod! Since we just learnt all about WAI, our first question should be: how does Yesod interact with WAI. The answer to that is with one very important function:
  
  