A Modal Analysis of Staged Computation

Abstract

We show that a type system based on the intuitionistic modal logic S4 provides an expressive framework for specifying and analyzing computation stages in the context of functional languages. Our main technical result is a conservative embedding of Nielson & Nielson's two-level functional language in our language Mini-ML, thus proving that binding-time correctness is equivalent to modal correctness on this fragment. In addition Mini-ML can also express immediate evaluation and sharing of code across multiple stages, thus supporting run-time code generation as well as partial evaluation.