Context-free session types

Abstract

Session types describe structured communication on heterogeneously typed channels at a high level. Their tail-recursive structure imposes a protocol that can be described by a regular language. The types of transmitted values are drawn from the underlying functional language, abstracting from the details of serializing values of structured data types. Context-free session types extend session types by allowing nested protocols that are not restricted to tail recursion. Nested protocols correspond to deterministic context-free languages. Such protocols are interesting in their own right, but they are particularly suited to describe the low-level serialization of tree-structured data in a type-safe way. We establish the metatheory of context-free session types, prove that they properly generalize standard (two-party) session types, and take first steps towards type checking by showing that type equivalence is decidable.