[Haskell-beginners] How to get qualifiers into type

I am playing around with some small graph theory problems. [Yeah I know there are good libraries -- as I said just playing around...] And I need to do things like type Vertex = Ix a => a (so that a vertex can be used to index an adjacency-list-array) That is to say that whenever 'Vertex' appears in a type signature, the Ix should 'float' out to the qualifier list After a lot of nudging from the error messages and rewriting as type Vertex = forall a. Ix a => a and giving options LANGUAGE RankNTypes, ImpredicativeTypes, LiberalTypeSynonyms I still get all kinds of errors. I'll report them if required. However first of all would like to know: Is this the way to go? Is this possible?