Prolog and Geometry Projects

Prolog is a userful tool for geometry and graphics implementations because its primitives, such as unification, match the requiements of many geometric algorithms. During the last two years, we have implemented programs to solve several problems in Prolog, including a subset of the Graphical Kernel System, convex-hull calculation, planar graph traversal, recognition of groupings of objects, Boolean combinations of polygons using multiple precision rational numbers, and cartographic map overlay. Certain paradigms or standard forms of geometric programming in Prolog are becoming evident. They include applying a function to every element of a set, executing a procedure so long as a certain geometric pattern exists, and using unification to propagate a transitive function. This article describes the experiences, including paradigms of programming that seem useful, and finally lists what we see as a advantaes and disadvantages of Prolog.