type synonyms in instances...

Is there any chance of enabling type synonyms in instance declarations. I remember a posting where is was stated that there was no technical reason for not being able to do this. Could we perhaps have a command line switch to enable this... For example, I think the following:- instance (HList e HNil) where ... is more readable as: type HSingleton e = HCons e HNil instance (HSingleton e) where ... Keean.