Static evaluation of functional programs

Abstract

Static evaluation underlies essentially all techniques for a priori semantic program manipulation, i.e. those that stop short of fully general execution. Included are such activities as type checking, partial evaluation, and, ultimately, optimized compilation. This paper describes a novel approach to static evaluation of programs in functional languages involving infinite data objects, i.e. those using normal order or "lazy" evaluation. Its principal features are abstract interpretation on a domain of demand patterns, and a notion of function "reversal". The latter associates with each function f a derived function f' mapping demand patterns on f to demand patterns on its formal parameter. This is used for a comprehensive form of strictness analysis, aiding in efficient compilation. This analysis leads to a revised notion of basic block, appropriate as an intermediate representation for a normal order functional language. An implementation of the analysis technique in Prolog is sketched, as well as an effort currently underway to apply the technique to the generation of optimized G-machine code.