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 the generic count problem using a pure PCF-like base language λ b and its extension with effect handlers λ h . We show that λ h admits an asymptotically more efficient implementation of generic count than any λ b implementation. We also show that this efficiency gap remains when λ b is extended with mutable state. To our knowledge this result is the first of its kind for control operators.