AHigh - Level Intermediate Language and the Algorithms for Compiling Finite - Domain Constraints 1

In this paper, we present a high-level intermediate language, called delay-Prolog, for implementing CLP(FD), the constraint language over nite-domains. Delay-Prolog has a much stronger description power than indexical, the intermediate language widely used in current nite-domain constraint compilers. It is powerful enough for describing all kinds of constraint propagation procedures, which by now have been mostly written in low level languages. And, most importantly, delay-Prolog opens new ways to compiling constraints. Besides the indexical algorithm that compiles constraints into indexicals, we implemented two new algorithms: the wait algorithm that compiles a constraint as whole into a propagation procedure without splitting it into small pieces, and the incremental simpli cation algorithm that incrementally simpli es constraints into smaller ones. The results are noteworthy: The wait algorithm generates the fastest code, while the widely used indexical algorithm generates code that is about 3 times slower than that generated by the wait algorithm. The wait algorithm is adopted in the latest version of B-Prolog. The experimental results show that B-Prolog is comparable in performance with the fastest CLP(FD) systems, although it is an emulated system.