Transforming constraint logic programs

A Folding Algorithm for Eliminating Existential Variables from Constraint Logic Programs

“…In this section we introduce our folding transformation rule which is a variant of the rules considered in the literature [7,8,9,10]. In particular, by using our variant of the folding rule we may replace a constrained goal occurring in the body of a clause where some existential variables occur, by an atom which has no existential variables in the folded clause.…”

“…This technique makes use of the definition, unfolding, and folding rules [5,6,7,8,9,10]. In this paper we have considered constraint logic programs, where the constraints are linear inequations over the rational (or real) numbers, and we have focused on the problem of automating the application of the folding rule.…”

“…In this paper we have considered constraint logic programs, where the constraints are linear inequations over the rational (or real) numbers, and we have focused on the problem of automating the application of the folding rule. Indeed, the applicability conditions of the many folding rules for transforming constraint logic programs which have been proposed in the literature [3,7,8,9,10], are specified in a declarative way and no algorithm is given to determine whether or not, given a clause γ to be folded by using a clause δ, one can actually perform that folding step. The problem of checking the applicability conditions of the folding rule is not trivial (see, for instance, the example presented in the Introduction).…”

“…The transformation techniques for the elimination of the existential variables make use of the unfolding and folding rules which have been first proposed in the context of functional programming by Burstall and Darlington [4], and then extended to logic programming [5,6] and to constraint logic programming [7,8,9,10]. In the techniques for eliminating existential variables a particularly relevant role is played by the folding rule, which can be defined as follows.…”

Transformations of CCP programs

“…Tamaki and Sato [1984] proposed a general framework for the unfold/fold transformation of logic programs, which has remained in the years the main historical reference of the field, and has later been extended to constraint logic programming (CLP) in [Maher 1993;Etalle and Gabbrielli 1996;Bensaou and Guessarian 1998] (for an overview of the subject, see the survey by Pettorossi and Proietti [1994]). As shown by a number of applications, these techniques provide a powerful methodology for the development and optimization of large programs, and can be regarded as the basic transformations techniques, which might be further adapted to be used for partial evaluation.…”