[Added EmbedAsAttr which allows you to embed attribute values that are in the XMLGenT monad
Jeremy Shaw <jeremy@seereason.com>**20100524180525
 Ignore-this: cc171b5a5d3a0206118e4835203cc403
 As describe in this thread:
 
 http://groups.google.com/group/happs/browse_thread/thread/bcc11209716b8126
 
 We sometimes wish to write code like this:
 
 page =
   ...
   <a href=fooURL>foo</a>
 
 fooURL = XMLGenT m String
 fooURL = return "http://example.org/foo"
 
 where the value of an attribute is calculated inside the XMLGenT monad.
 
 We already have this instance for EmbedAsChild:
 instance (EmbedAsChild m c, TypeCastM m1 m) => EmbedAsChild m (XMLGenT m1 c)
 
 We add a similar instance for EmbedAsAttr:
 
 instance (EmbedAsAttr m (Attr a v), TypeCastM m1 m) => EmbedAsAttr m (Attr a (XMLGenT m1 v))
] hunk ./src/HSX/XMLGenerator.hs 104
+instance (EmbedAsAttr m (Attr a v), TypeCastM m1 m) => EmbedAsAttr m (Attr a (XMLGenT m1 v)) where
+ asAttr (a := (XMLGenT m1a)) = do
+            v <- XMLGenT $ typeCastM m1a
+            asAttr (a := v)
+