On the Expressiveness of Forwarding in Higher-Order Communication (December 6, 2009)

In higher-order process calculi the values exchanged in communications may contain processes. There are only two capabilities for received processes: execution and forwarding. Here we propose a limited form of forwarding: output actions can only communicate the parallel composition of statically known closed processes and processes received through previously executed input actions. We study the expressiveness of a higher-order process calculus featuring this style of communication. Our main result shows that in this calculus termination is decidable while convergence is undecidable. Then, as a way of recovering the expressiveness loss due to limited forwarding, we extend the calculus with a form of process suspension called passivation. Somewhat surprisingly, in the calculus extended with passivation both termination and convergence are undecidable.