Tabulation of Functions in Definite Clause Programs

An extended version of the applicative caching technique from functional programming is adapted to OLD resolution as an alternative to OLDT resolution for predicates that are actually functions. An inference system, OLDTF resolution, is given with a proof procedure. It is argued why this special case is interesting in its own right also outside the area of deductive databases. It is outlined how special cases of our technique can be used to declaratively incorporate eecient data structures with state in logic programs. 1 Introduction In a programming language with referential transparency, an expression can be replaced with any other expression that has the same meaning. Tabulation in functional programming In functional programming languages this has been exploited through a technique called tabulation or memoing 6, 15, 18, 23]. This means to maintain, for selected functions, a table of pairs of domain-codomain elements that have already been computed. Further applications of the function to values for which there are \cached" results can be solved by simple table look-ups. The motivation is to speed up execution of programs by avoid recompu-tation of function applications, at the expense of using more space.