Computer Science Technical Reports New Versions of Ask and Tell for Synchronous Communication in Concurrent Constraint Programming New Versions of Ask and Tell for Synchronous Communication in Concurrent Constraint Programming

Concurrent constraint programming is classically based on asynchronous communication via a shared store. This paper presents new versions of the ask and tell primitives which features synchronicity. Our approach is based on the idea of telling new information just in the case that a concurrently running process is asking for it. The new primitives are shown to be simple yet expressive enough to code signiicant problems. Two semantics for them are proposed. The rst one is of an operational nature and formalises computations by means of a transition system. It is not compositional. This problem is addressed in another semantics which beneets from hypotheses made both on concurrent processes and the state of the store rather than on its successive updates.