CPS Translations and Applications: The Cube and Beyond

Abstract

Continuation passing style (CPS) translations of typed λ-calculi have numerous applications. However, the range of these applications has been confined by the fact that CPS translations are known for non-dependent type systems only, thus excluding well-known systems like the calculus of constructions (CC) and the logical frameworks (LF). This paper presents techniques for CPS translating systems with dependent types, with an emphasis on pure type-theoretical applications. In the first part of the paper we review several lines of work in which the need for CPS translations of dependent type systems has arisen, and discuss the difficulties involved with CPS translating such systems. One way of overcoming these difficulties is to work with so-called domain-free type systems. Thus, instead of Barendregt‘s λ-cube we shall consider the domain-free λ-cube, and instead of traditional pure type systems, we shall consider domain-free pure type systems. We therefore begin the second part by reviewing the domain-free λ-cube, which includes domain-free versions of CC and LF, and then present CPS translations for all the systems of the domain-free λ-cube. We also introduce Direct Style (DS) (i.e., inverse CPS) translations for all the systems of the domain-free λ-cube; such DS translations, which have been used in a number of applications, were previously formulated for untyped and simply-typed languages only. In the third part we review domain-free pure type systems and generalize the CPS translations of the domain-free λ-cube to a large class of domain-free pure type systems which includes most of the systems that appear in the literature, including those of the domain-free λ-cube. Many translations that appear in the literature arise as special cases of ours. In the fourth part of the paper we present two approaches to CPS translations of traditional pure type systems. The first, indirect, technique lifts the CPS translation of domain-free pure type systems to the analogous class of traditional pure type systems by using results that relate derivations in domain-free and traditional pure type systems. The second, direct, approach translates derivations, requiring a certain order on derivations to be well-founded. Both techniques yield translations for most of the systems that appear in the literature, including those of Barendregt‘s λ-cube.