I have defined a function on types thanks to functional dependencies. I use it like that: myFunction :: (TypeFunction MyComplexType f) => f -> f f is unique for MyComplexType. Is there a way to name f ? I would like to write: myFunction :: SimplifiedType -> SimplifiedType where TypeFunction MyComplexType SimplifiedType is an instance of the class TypeFunction. Of course, I don't want to write explicitly SimplifiedType otherwise I could just do type SimplifiedType = ... The idea is that I build a MyComplexType using type synonyms and type constructors. But, the result has a shape which is too complex. I simplify it into a canonical form that I can use in some algorithms at the type level. I suspect I will have to use the type constraint and that there is no way to name the result of a computation at the type level ? Thanks, Christophe.