Full integration of subtyping and if-expression

  • Authors:

  • Gang Chen

  • Affiliations:

  • Boston University, Boston, MA

  • Venue:
  • Proceedings of the 4th ACM SIGPLAN international conference on Principles and practice of declarative programming
  • Year:
  • 2002

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Abstract

The combination of full subsumption and conditional expression is a challenging problem, because in such a system, a term might not have a type which is a representative of all types of the term. Therefore, the traditional type checking technique fails. Due to such a difficulty, Java typing rule for if-expression uses only a restricted form of subtyping. In this paper, we propose a type system which includes both of the above mentioned features and enjoys decidable type checking. We also show that the system has the subject reduction property. It is expected that this technique could be used to improve the type system of Java with full subsumption.