A POLYMORPHIC TYPE SYSTEM WITH CONSTRAINTS

This paper concentrates on a polymorphic type system with constraints based on constrained types. By Incorporating constraints into universal quantification, the system can make applications of parametrically polymorphic function more safe. The constrained types provide a new way for expressing and implementing overloading. The Incorporating can improve the expressiveness of types. There are two layers with different type structures in the type system given in this paper. Introduction and elimination of constraints are in the different levels. It is proved that the satisfiability of constraints in W, which is a type checking algorithm proposed in the paper,is decidable.