Hybrid Constraints for Regular Terms

We define a family of constraints over the domain of regular terms. This family is built by extending equality with general constraints over root labels. We say that the resulting constraints are hybrid. Under the assumption that these constraints are stable with respect to a partial ordering we give an efficient constraint solver for hybrid constraints. We show in an example how the constraint technique is used in a type inference algorithm, and that stable hybrid constraint can be used for the type inference of the λμ-calculus extended with overloaded operators. The same technique applies to type inference of Pascal.