Stratified operational semantics for safety and correctness of the region calculus

Abstract

The region analysis of Tofte and Talpin is an attempt to determine statically the life span of dynamically allocated objects. But the calculus is at once intuitively simple, yet deceptively subtle, and previous theoretical analyses have been frustratingly complex: no analysis has revealed and explained in simple terms the connection between the subleties of the calculus and the imperative features it builds on. We present a novel approach for proving safety and correctness of a simplified version of the region calculus. We give a stratified operational semantics, composed of a highlevel semantics dealing with the conceptual difficulties of effect annotations, and a low-level one with explicit operations on a region-indexed store. The main results of the paper are a proof simpler than previous ones, and a modular approach to type safety and correctness. The flexibility of this approach is demonstrated by the simplicity of the extension to the full calculus with type and region polymorphism.