Orthogonal type extensions and reductions

In this paper we present a generalization of Oberon's record type extensions. Our extension mechanism is orthogonally applicable to all the conventional data types found in Pascal-like languages. In order to balance the type system, we present an inverse concept, type reductions, that also can be applied to all the programmer-defined data types. These concepts provide flexible and powerful means for expressing universal subtyping and supertyping in a statically-typed programming language, as well as many possibilities for reuse of data types via a sound mathematical characterization of assignment statements. The presented ideas are under implementation in Alberich, a programming language that can be considered as a natural descendant of Oberon.