Types for Complexity of Parallel Computation in Pi-Calculus

Abstract

Type systems as a technique to analyse or control programs have been extensively studied for functional programming languages. In particular, some systems allow one to extract from a typing derivation a complexity bound on the program. We explore how to extend such results to parallel complexity in the setting of pi-calculus, considered as a communication-based model for parallel computation. Two notions of time complexity are given: the total computation time without parallelism (the work) and the computation time under maximal parallelism (the span). We define operational semantics to capture those two notions and present two type systems from which one can extract a complexity bound on a process. The type systems are inspired both by sized types and by input/output types, with additional temporal information about communications.