Analysis of polymorphically typed logic programs using ACI-unification

Abstract

Analysis of (partial) groundness is an important application of abstract interpretation. There are several proposals for improving the precision of such an analysis by exploiting type information, including our own work [15], where we had shown how the information present in the type declarations of a program can be used to characterise the degree of instantiation of a term in a precise but finite way. This approach worked for polymorphically typed logic programs. Here, we recast this approach following [5,11]. To formalise which properties of terms we want to characterise, we use labelling functions, which are functions that extract subterms from a term along certain paths. An abstract term collects the results of all labelling functions of a term. For the analysis, programs are executed on abstract terms instead of the concrete ones, and usual unification is replaced by unification modulo an equality theory which includes the well-known ACI-theory. Thus we generalise [5,11] w.r.t. the type systems considered and relate those two works.