Memoryful geometry of Interaction II: recursion and adequacy

Abstract

A general framework of Memoryful Geometry of Interaction (mGoI) is introduced recently by the authors. It provides a sound translation of lambda-terms (on the high-level) to their realizations by stream transducers (on the low-level), where the internal states of the latter (called memories) are exploited for accommodating algebraic effects of Plotkin and Power. The translation is compositional, hence ``denotational,'' where transducers are inductively composed using an adaptation of Barbosa's coalgebraic component calculus. In the current paper we extend the mGoI framework and provide a systematic treatment of recursion---an essential feature of programming languages that was however missing in our previous work. Specifically, we introduce two new fixed-point operators in the coalgebraic component calculus. The two follow the previous work on recursion in GoI and are called Girard style and Mackie style: the former obviously exhibits some nice domain-theoretic properties, while the latter allows simpler construction. Their equivalence is established on the categorical (or, traced monoidal) level of abstraction, and is therefore generic with respect to the choice of algebraic effects. Our main result is an adequacy theorem of our mGoI translation, against Plotkin and Power's operational semantics for algebraic effects.