Adding WAM instructions to support Valued Clauses for the Relational/Functional Integration Language RELFUN

Abstract

The integration of functional and relational programming languages is mainly based on interpreter systems. This work shows how to add instructions to the abstract PROLOG machine WAM, introduced by David H. D. Warren [11], for compiling the integration language RELFUN. In the relational view of computation, the binding of variables 1s one of the basic concepts, whereas the functional view is based on the returning of values. RELFUN is built around valued clauses, i.e. the last call of a clause determines the value of the clause. In this paper "VALREG" instructions are introduced to support valued clauses in a WAM based machine, developing a proposal originally made by Harold Boley [2] for the Prolog machine model (WPE) of David Maier and David S. Warren [5]. It is shown that these instructions are integrated easily into the existing WAM model and that the compilation of RELFUN Programs is straightforward. The added instructions were implemented in LISP for the Sven-Olof Nystroem based WAM model ([12]) and for a WAM extension, the Joachim Beer based model ([9],[10],[13]).