Higher-order hierarchies

Abstract

This paper introduces the notion of higher-order inheritance hierarchies. They are useful because they provide well-known benefits of object-orientation at the level of entire hierarchies - benefits which are not available with current approaches. Three facets must be adressed: First, it must be possible to create hierarchies incrementally based on existing hierarchies, such that commonalities are expressed via reuse, not duplication. Second, the hierarchies must themselves be organized into hierarchies, such that their relationships are made explicit and can be exploited in a type safe manner. Finally, it must be possible to write generic code that works on every hierarchy derived from the hierarchy for which it was written. This paper presents a language design that supports such a notion of higher-order hierarchies. It has been implemented in context of a full-fledged, statically typed language. © Springer-Verlag Berlin Heidelberg 2003.