Open and Closed Worlds for Overloading: a Definition and Support for Coexistence
Дата
Авторы
Camarão,Carlos
Vasconcellos,Cristiano
Figueiredo,Lucília
Nicola,João
Journal Title
Journal ISSN
Volume Title
Издатель
Journal of Universal Computer Science
Аннотация
Описание
The type system of Haskell and some related systems are based on an open world approach for overloading. In an open world, the principal type of each overloaded symbol must be explicitly annotated (in Haskell, annotations occur in type class declarations) and a definition of an overloaded symbol is required to exist only when overloading is resolved. In a closed world, on the other hand, each principal type is determined according to the types of definitions that exist in the relevant context and, furthermore, overloading resolution for an expression considers only the context of the definition of its constituent symbols. In this paper we formally characterize open and closed worlds, and discuss their relative advantages. We present a type system that supports both approaches together, and compare the defined system with Haskell type classes extended with multi-parameter type classes and functional dependencies. We show in particular that functional dependencies are not necessary in order to support multi-parameter type classes, and present an alternative route.
Ключевые слова
type system , type inference , constrained polymorphism , closed and open world approaches for overloading