Type inference with constrained types

In this paper we present a general framework HM(X) for Hindley/Milner style type systems with constraints, analogous to the CLP(X) framework in constrained logic programming. We present sufficient conditions on the constraint domain X so that the principal types property carries over to HM(X). The conditions turn out to be fairly simple and natural. The usage of the aproach is demonstrated in instantion of parameter X with several known type disciplines. We consider extensible records, typeclasses, overloading and subtyping