Cooperation of Constraint Solvers: Using the New Process Control Facilities of ELAN

Abstract

In this paper, we introduce new process control facilities in the ELAN language as low-level primitives and high-level concurrent strategies. The low-level primitives are similar to those existing in UNIX for process control and communication. The high-level concurrent strategies proposed in this paper extend their existing sequential version giving them a new behaviour while preserving their operational semantics. This extension of the ELAN language allows to prototype in a very abstract and flexible way the integration of several computational systems within the same rewriting framework. Using the high-level concurrent strategies we can also avoid some non-terminating processes and/or apply the most efficient rewrite rule or strategy. We exemplify their use by prototyping different kinds of cooperation between constraint solvers, e.g. sequential and concurrent solvers.We are grateful to Hélène Kirchner, Claude Kirchner, and Christophe Ringeissen for providing useful comments on an earlier version of this paper, and to the anonymous referees for their remarks that allowed us to improve this work.