Representing Objects in a Logic Programming Language With Scoping Constructs

We present a logic programming language that uses implications and universal quantifiers in goals and in the bodies of clauses to provide a simple scoping mechanism for program clauses and constants. Within this language it is possible to define a simple notion of parametric module and local constant. Given this ability to structure programs, we explore how object-oriented programming, where objects are viewed as abstractions with behaviors, state, and inheritance, might be accommodated. To capture the notion of mutable state, we depart from the pure logic setting by adding a declaration that certain local predicates are deterministic (they succeed at most once). This declaration, along with a goal-continuation passing style of programming is adequate to model the state of objects. We also examine a few aspects of how having objects embedded in logic programming can be used to enrich the notion of object: for example, objects may be partial (that is, may contain free variables) and non-deterministic, and it is possible not only to search for objects with certain properties but also to do hypothetical reasoning about them.