Decidability and syntactic control of interference

We investigate the decidability of observational equivalence and approximation in Reynolds' "Syntactic Control of Interference" (SCI), a prototypical functionalimperative language in which covert interference between functions and their arguments is prevented by the use of an affine typing discipline. iating denotations of terms in a fully abstract "relational" model of finitary basic SCI (due to Reddy) with multitape finite state automata, we show that observational approximation is not decidable (even at first order), but that observational equivalence is decidable for all terms. We then consider the same problems for basic SCI extended with non-local control in the form of backwards jumps. We show that both observational approximation and observational equivalence are decidable in this "observably sequential" version anguage by describing a fully abstract games model in which strategies are regular languages.

• Type: Journal
• Year: 2008
• Where: TCS
• Authors: James Laird
• Keywords: Basic Sci, Observational Approximation, Observational Equivalence, TCS 2008, Theoretical Computer Science