The Update Calculus (Extended Abstract)

In the update calculus concurrent processes can perform update actions with side eeects, and a scoping operator can be used to control the extent of the update. In this way it incorporates fundamental concepts both from imperative languages or concurrent constraints formalisms , and from functional formalisms such as the-and-calculi. Structurally it is similar to but simpler than the-calculus; it has only one binding operator and a symmetry between input and output. We deene the structured operational semantics and the proper bisimula-tion equivalence and congruence, and give a complete axiomatization. The-calculus turns out to be an asymmetric subcalculus.