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ABSTRACT

Extensive research efforts have been devoted to implement a group of type-safe mutually recursive classes; recently, proposals for separating each member of the group as a reusable and composable programming unit have also been presented. One problem of these proposals is verbosity of the source programs; we have to declare a recursive type parameter to parameterize each mutually recursive class within each class declaration, and we have to declare a fixed-point class with empty class body for each parameterized class. Therefore, even though the underlying type system is simple, programs written in these languages tend to be rather complex and hard to understand. In this paper, we propose a language with lightweight dependent classes that forms a simple type system built on top of generic Java. In this language, we can implement each member of type-safe mutually recursive classes in a separate source file without writing a lot of complex boilerplate code. To carefully investigate type soundness of our proposal, we develop X.FGJ, a simple extension of FGJ supporting lightweight dependent classes. This type system is proved to be sound.

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INDEX TERMS

Primary Classification:
  D. Software
  D.1 PROGRAMMING TECHNIQUES
      D.1.5 Object-oriented Programming

Additional Classification:
  D. Software
  D.3 PROGRAMMING LANGUAGES
      D.3.1 Formal Definitions and Theory
      D.3.3 Language Constructs and Features

General Terms:
Languages

Keywords:
class-based languages, dependent classes, generics, mutually recursive extensions, type safety