A Diamond Machine for Strong Evaluation

BENIAMINO ACCATTOLI; PABLO BARENBAUM

Taipei

Conferencia; 21st Asian Symposium on Programming Languages and Systems (APLAS); 2023

Academia Sinica

Abstract machines for strong evaluation of the λ-calculus enter into arguments and have a set of transitions for backtracking out of an evaluated argument. We study a new abstract machine which avoids backtracking by splitting the run of the machine in smaller jobs, one for argument, and that jumps directly to the next job once one is finished. Usually, machines are also deterministic and implement deterministic strategies. Here we weaken this aspect and consider a light form of non- determinism, namely the diamond property, for both the machine and the strategy. For the machine, this introduces a modular management of jobs, parametric in a scheduling policy. We then show how to obtain various strategies, among which leftmost-outermost evaluation, by instantiating in different ways the scheduling policy.