PolyTOIL: A type-safe polymorphic object-oriented language

Abstract

PolyTOIL is a new statically typed polymorphic object-oriented programming language that is provably typesafe. By separating the definitions of subtyping and inheritance, providing a name for the type of self, and carefully defining the type-checking rules, we have obtained a language that is very expressive while supporting modular type-checking of classes. Thematchingrelation on types, which is related to F-bounded quantification, is used both in stating type-checking rules and expressing the bounds on type parameters for polymorphism. The design of PolyTOIL is based on a careful formal definition of type-checking rules and semantics. A proof of type safety is obtained with the aid of a subject reduction theorem.