Program transformations and WAM-support for the compilation of definite metaprograms

Abstract

By combining binarization and elimination of metavariables we compile definite metaprograms to equivalent definite binary programs, while preserving first argument indexing. The transformation gives a faithful embedding of the essential ingredient of full Prolog to the more restricted class of binary definite programs while preserving a strong operational equivalence with the original program. The resulting binary programs can be executed efficiently on a considerably simplified WAM. We describe WAM-support that avoids increasing code size by virtualizing links between predicate and functor occurrences that result in the binarization process. To improve the space-efficiency of our run-time system we give a program transformation that simulates resourcedriven failure while keeping conditional answers. Then we describe the WAM-support needed to implement the transformation efficiently. We also discuss its applications to parallel execution of binary programs and as a surprisingly simple garbage collection technique that works in time proportional to the size of useful data.