Typing references by effect inference

Abstract

Hindley/Milner-style polymorphism is a simple, natural, and flexible type discipline for functional languages, but incorporating imperative extensions is difficult. We present a new technique for typing references in the presence of polymorphism by inferring a concise summary of each expression's allocation behavior—a type effect. A simple technique for proving soundness with respect to a reduction semantics demonstrates that the type system prevents type errors. By establishing that the system corresponds to an alternate system better suited to implementation, we obtain an algorithm to perform type and effect inference.