The Translation Power of the Futamura Projections

Despite practical successes with the Futamura projections, it has been an open question whether target programs produced by specializing interpreters can always be as efficient as those produced by a translator. We show that, given a Jones-optimal program specializer with static expression reduction, there exists for every translator an interpreter which, when specialized, can produce target programs that are at least as fast as those produced by the translator. This is not the case if the specializer is not Jones-optimal. We also examine Ershov’s generating extensions, give a parameterized notion of Jones optimality, and show that there is a class of specializers that can always produce residual programs that match the size and time complexity of programs generated by an arbitrary generating extension. This is the class of generation universal specializers. We study these questions on an abstract level, independently of any particular specialization method.