Effects for efficiency: asymptotic speedup with first-class control

Abstract

We study the fundamental efficiency of delimited control. Specifically, we show that effect handlers enable an asymptotic improvement in runtime complexity for a certain class of functions. We consider thegeneric countproblem using a pure PCF-like base language λband its extension with effect handlers λh.We show that λhadmits an asymptotically more efficient implementation of generic count than any λbimplementation.We also show that this efficiency gap remains when λbis extended with mutable state.To our knowledge this result is the first of its kind for control operators.