Appears in PhysComp96 Workshop on Physics and Computation A logically reversible evaluator for the call-by-name lambda calculus

We present an evaluator for the call-by-name lambda calculus that is logically reversible. This evaluator is therefore a candidate for a computation mechanism that does not dissipate energy due to information erasure. Our design extends Landin's SECD evaluator for the lambda calculus with a history tape H|as in Bennett's constructions of reversible Turing machines|and is hence called SECD-H. The history tape records su cient information to supply each state of a computation with a unique predecessor state. H can therefore be used to reverse the computation and to reset the machine. Since the lambda calculus is a model for realistic programming languages, SECD-H can, unlike a reversible TM, be directly used to simulate reversible computation of large and complex programs. We provide a complete implementation of SECD-H for such purposes.